[v2,02/18] gpio: uapi: define uAPI v2

Add a new version of the uAPI to address existing 32/64-bit alignment
issues, add support for debounce and event sequence numbers, and provide
some future proofing by adding padding reserved for future use.

The alignment issue relates to the gpioevent_data, which packs to different
sizes on 32-bit and 64-bit platforms. That creates problems for 32-bit apps
running on 64-bit kernels.  The patch addresses that particular issue, and
the problem more generally, by adding pad fields that explicitly pad
structs out to 64-bit boundaries, so they will pack to the same size now,
and even if some of the reserved padding is used for __u64 fields in the
future.

The lack of future proofing in v1 makes it impossible to, for example,
add the debounce feature that is included in v2.
The future proofing is addressed by providing reserved padding in all
structs for future features.  Specifically, the line request,
config, info, info_changed and event structs receive updated versions,
and the first three new ioctls.

Signed-off-by: Kent Gibson <warthog618@gmail.com>
---

I haven't added any padding to gpiochip_info, as I haven't seen any calls
for new features for the corresponding ioctl, but I'm open to updating that
as well.

As the majority of the structs and ioctls were being replaced, it seemed
opportune to rework some of the other aspects of the uAPI.

Firstly, I've reworked the flags field throughout.  v1 has three different
flags fields, each with their own separate bit definitions.  In v2 that is
collapsed to one.

I've also merged the handle and event requests into a single request, the
line request, as the two requests were mostly the same, other than the
edge detection provided by event requests.  As a byproduct, the v2 uAPI
allows for multiple lines producing edge events on the same line handle.
This is a new capability as v1 only supports a single line in an event
request.

This means there are now only two types of file handle to be concerned with,
the chip and the line, and it is clearer which ioctls apply to which type
of handle.

There is also some minor renaming of fields for consistency compared to
their v1 counterparts, e.g. offset rather than lineoffset or line_offset,
and consumer rather than consumer_label.

Additionally, v1 GPIOHANDLES_MAX becomes GPIOLINES_MAX in v2 for clarity,
and the gpiohandle_data __u8 array becomes a bitmap gpioline_values.

The v2 uAPI is mostly just a reorganisation of v1, so userspace code,
particularly libgpiod, should easily port to it.

Changes since v1:
 - lower case V1 and V2, except in capitalized names
 - hyphenate 32/64-bit
 - rename bitmap field to bits
 - drop PAD_SIZE consts in favour of hard coded numbers
 - sort includes
 - change config flags to __u64
 - increase padding of gpioline_event
 - relocate GPIOLINE_CHANGED enum into v2 section (is common with v1)
 - rework config to collapse direction, drive, bias and edge enums back
   into flags and add optional attributes that can be associated with a
   subset of the requested lines.

Changes since the RFC:
 - document the constraints on array sizes to maintain 32/64 alignment
 - add sequence numbers to gpioline_event
 - use bitmap for values instead of array of __u8
 - gpioline_info_v2 contains gpioline_config instead of its composite fields
 - provide constants for all array sizes, especially padding
 - renamed "GPIOLINE_FLAG_V2_KERNEL" to "GPIOLINE_FLAG_V2_USED"
 - renamed "default_values" to "values"
 - made gpioline_direction zero based
 - document clock used in gpioline_event timestamp
 - add event_buffer_size to gpioline_request
 - rename debounce to debounce_period
 - rename lines to num_lines
 
 include/uapi/linux/gpio.h | 284 ++++++++++++++++++++++++++++++++++++--
 1 file changed, 270 insertions(+), 14 deletions(-)

On Sat, Jul 25, 2020 at 6:20 AM Kent Gibson <warthog618@gmail.com> wrote:
>
> Add a new version of the uAPI to address existing 32/64-bit alignment
> issues, add support for debounce and event sequence numbers, and provide
> some future proofing by adding padding reserved for future use.
>
> The alignment issue relates to the gpioevent_data, which packs to different
> sizes on 32-bit and 64-bit platforms. That creates problems for 32-bit apps
> running on 64-bit kernels.  The patch addresses that particular issue, and
> the problem more generally, by adding pad fields that explicitly pad
> structs out to 64-bit boundaries, so they will pack to the same size now,
> and even if some of the reserved padding is used for __u64 fields in the
> future.
>
> The lack of future proofing in v1 makes it impossible to, for example,
> add the debounce feature that is included in v2.
> The future proofing is addressed by providing reserved padding in all
> structs for future features.  Specifically, the line request,
> config, info, info_changed and event structs receive updated versions,
> and the first three new ioctls.
>
> Signed-off-by: Kent Gibson <warthog618@gmail.com>
> ---

Hi Kent,

Thanks a lot for your work on this. Please see comments below.

One thing I'd change globally for better readability is to have all
new symbols marked as v2 - even if they have no counterparts in v1. I
know libgpiod will wrap it all anyway but I think it's still a good
way to make our work in user-space easier.

>
> I haven't added any padding to gpiochip_info, as I haven't seen any calls
> for new features for the corresponding ioctl, but I'm open to updating that
> as well.
>
> As the majority of the structs and ioctls were being replaced, it seemed
> opportune to rework some of the other aspects of the uAPI.
>
> Firstly, I've reworked the flags field throughout.  v1 has three different
> flags fields, each with their own separate bit definitions.  In v2 that is
> collapsed to one.
>
> I've also merged the handle and event requests into a single request, the
> line request, as the two requests were mostly the same, other than the
> edge detection provided by event requests.  As a byproduct, the v2 uAPI
> allows for multiple lines producing edge events on the same line handle.
> This is a new capability as v1 only supports a single line in an event
> request.
>
> This means there are now only two types of file handle to be concerned with,
> the chip and the line, and it is clearer which ioctls apply to which type
> of handle.
>
> There is also some minor renaming of fields for consistency compared to
> their v1 counterparts, e.g. offset rather than lineoffset or line_offset,
> and consumer rather than consumer_label.
>
> Additionally, v1 GPIOHANDLES_MAX becomes GPIOLINES_MAX in v2 for clarity,
> and the gpiohandle_data __u8 array becomes a bitmap gpioline_values.
>
> The v2 uAPI is mostly just a reorganisation of v1, so userspace code,
> particularly libgpiod, should easily port to it.
>

I think the info above is worth putting into the commit message.
Especially the part about merging the two event types.

> Changes since v1:
>  - lower case V1 and V2, except in capitalized names
>  - hyphenate 32/64-bit
>  - rename bitmap field to bits
>  - drop PAD_SIZE consts in favour of hard coded numbers
>  - sort includes
>  - change config flags to __u64
>  - increase padding of gpioline_event
>  - relocate GPIOLINE_CHANGED enum into v2 section (is common with v1)
>  - rework config to collapse direction, drive, bias and edge enums back
>    into flags and add optional attributes that can be associated with a
>    subset of the requested lines.
>
> Changes since the RFC:
>  - document the constraints on array sizes to maintain 32/64 alignment
>  - add sequence numbers to gpioline_event
>  - use bitmap for values instead of array of __u8
>  - gpioline_info_v2 contains gpioline_config instead of its composite fields
>  - provide constants for all array sizes, especially padding
>  - renamed "GPIOLINE_FLAG_V2_KERNEL" to "GPIOLINE_FLAG_V2_USED"
>  - renamed "default_values" to "values"
>  - made gpioline_direction zero based
>  - document clock used in gpioline_event timestamp
>  - add event_buffer_size to gpioline_request
>  - rename debounce to debounce_period
>  - rename lines to num_lines
>
>  include/uapi/linux/gpio.h | 284 ++++++++++++++++++++++++++++++++++++--
>  1 file changed, 270 insertions(+), 14 deletions(-)
>
> diff --git a/include/uapi/linux/gpio.h b/include/uapi/linux/gpio.h
> index 285cc10355b2..3f6db33014f0 100644
> --- a/include/uapi/linux/gpio.h
> +++ b/include/uapi/linux/gpio.h
> @@ -12,10 +12,13 @@
>  #define _UAPI_GPIO_H_
>
>  #include <linux/ioctl.h>
> +#include <linux/kernel.h>
>  #include <linux/types.h>
>
>  /*
>   * The maximum size of name and label arrays.
> + *
> + * Must be a multiple of 8 to ensure 32/64-bit alignment of structs.
>   */
>  #define GPIO_MAX_NAME_SIZE 32
>
> @@ -32,6 +35,251 @@ struct gpiochip_info {
>         __u32 lines;
>  };
>
> +/*
> + * Maximum number of requested lines.
> + *
> + * Must be a multiple of 8 to ensure 32/64-bit alignment of structs.
> + */
> +#define GPIOLINES_MAX 64
> +
> +/* The number of __u64 required for a bitmap for GPIOLINES_MAX lines */
> +#define GPIOLINES_BITMAP_SIZE  __KERNEL_DIV_ROUND_UP(GPIOLINES_MAX, 64)
> +

In what circumstances can this be different than 1? It's worth
documenting here I suppose.

> +/*
> + * The maximum number of configuration attributes associated with a line
> + * request.
> + */
> +#define GPIOLINE_NUM_ATTRS_MAX 10
> +

How did you choose this number? I mean: it's reasonable - just asking
for clarification.

> +/**
> + * enum gpioline_flag_v2 - &struct gpioline_attribute.flags values
> + */
> +enum gpioline_flag_v2 {
> +       GPIOLINE_FLAG_V2_USED                   = 1UL << 0, /* line is not available for request */
> +       GPIOLINE_FLAG_V2_ACTIVE_LOW             = 1UL << 1,
> +       GPIOLINE_FLAG_V2_INPUT                  = 1UL << 2,
> +       GPIOLINE_FLAG_V2_OUTPUT                 = 1UL << 3,
> +       GPIOLINE_FLAG_V2_EDGE_RISING            = 1UL << 4,
> +       GPIOLINE_FLAG_V2_EDGE_FALLING           = 1UL << 5,
> +       GPIOLINE_FLAG_V2_OPEN_DRAIN             = 1UL << 6,
> +       GPIOLINE_FLAG_V2_OPEN_SOURCE            = 1UL << 7,
> +       GPIOLINE_FLAG_V2_BIAS_PULL_UP           = 1UL << 8,
> +       GPIOLINE_FLAG_V2_BIAS_PULL_DOWN         = 1UL << 9,
> +       GPIOLINE_FLAG_V2_BIAS_DISABLED          = 1UL << 10,
> +};
> +
> +/**
> + * struct gpioline_values - Values of GPIO lines
> + * @bits: a bitmap containing the value of the lines, set to 1 for active
> + * and 0 for inactive.  Note that this is the logical value, which will be
> + * the opposite of the physical value if the line is configured as active
> + * low.
> + */
> +struct gpioline_values {
> +       __u64 bits[GPIOLINES_BITMAP_SIZE];
> +};
> +

We can set values only for a subset of requested lines but AFAICT we
can't read values of only a subset of lines. Would it be difficult to
remove this limitation? While reading values always succeeds - even if
the line is in input mode and has edge detected - I think that someone
may want to request the max number of lines without reading all their
values each time. Maybe consider merging this with struct
gpioline_set_values?

> +/**
> + * struct gpioline_set_values - Values to set a group of GPIO lines
> + * @mask: a bitmap identifying the lines to set.
> + * @bits: a bitmap containing the value of the lines, set to 1 for active
> + * and 0 for inactive.  Note that this is the logical value, which will be
> + * the opposite of the physical value if the line is configured as active
> + * low.
> + */
> +struct gpioline_set_values {
> +       __u64 mask[GPIOLINES_BITMAP_SIZE];
> +       __u64 bits[GPIOLINES_BITMAP_SIZE];
> +};
> +
> +/**
> + * enum gpioline_attr_id - &struct gpioline_attribute.id values
> + */
> +enum gpioline_attr_id {
> +       GPIOLINE_ATTR_ID_FLAGS                  = 1,
> +       GPIOLINE_ATTR_ID_OUTPUT_VALUES          = 2,
> +       GPIOLINE_ATTR_ID_DEBOUNCE               = 3,
> +};
> +
> +/**
> + * struct gpioline_attribute - a configurable attribute of a line
> + * @id: attribute identifier with value from &enum gpioline_attr_id
> + * @padding: reserved for future use and must be zero filled
> + * @flags: if id is GPIOLINE_ATTR_ID_FLAGS, the flags for the GPIO line,
> + * with values from enum gpioline_flag_v2, such as
> + * GPIOLINE_FLAG_V2_ACTIVE_LOW, GPIOLINE_FLAG_V2_OUTPUT etc, OR:ed
> + * together.  This overrides the default flags contained in the &struct
> + * gpioline_config for the associated line.
> + * @values: if id is GPIOLINE_ATTR_ID_OUTPUT_VALUES, the values to which
> + * the lines will be set
> + * @debounce_period: if id is GPIOLINE_ATTR_ID_DEBOUNCE, the desired
> + * debounce period, in microseconds
> + */
> +struct gpioline_attribute {
> +       __u32 id;
> +       __u32 padding;
> +       union {
> +               __u64 flags;
> +               struct gpioline_values values;
> +               __u32 debounce_period;
> +       };
> +};

I'm afraid that if we don't have enough padding here (at the end),
we'll end up wanting to add a new attribute at some point whose
argument won't fit. Maybe have a specific field in the union that's
even larger than __u64?

> +
> +/**
> + * struct gpioline_config_attribute - a configuration attribute associated
> + * with one or more of the requested lines.
> + * @mask: a bitmap identifying the lines to which the attribute applies
> + * @attr: the configurable attribute
> + */
> +struct gpioline_config_attribute {
> +       __u64 mask[GPIOLINES_BITMAP_SIZE];
> +       struct gpioline_attribute attr;
> +};
> +
> +/**
> + * struct gpioline_config - Configuration for GPIO lines
> + * @flags: flags for the GPIO lines, with values from enum
> + * gpioline_flag_v2, such as GPIOLINE_FLAG_V2_ACTIVE_LOW,
> + * GPIOLINE_FLAG_V2_OUTPUT etc, OR:ed together.  This is the default for
> + * all requested lines but may be overridden for particular lines using
> + * attrs.

So I'm having a hard time with this. I understand that the thinking
behind it was: use the flags field to set all lines to INPUT by
default and only set certain lines to OUTPUT with attrs. This would
make life easier for user-space but it complicates the kernel code and
I also believe that any such simplification should be handled by
user-space libraries, not be exposed by kernel uAPI. My personal
preference would be to drop the flags field and only handle attributes
(maybe even define a special macro to set all bits in mask -
GPIOLINE_CONFIG_ALL_LINES or something) on a first-in-wins basis. I'm
open to other suggestions though.

> + * @num_attrs: the number of attributes in attrs
> + * @padding: reserved for future use and must be zero filled
> + * @attrs: the configuration attributes associated with the requested
> + * lines.
> + */
> +struct gpioline_config {
> +       __u64 flags;
> +       __u32 num_attrs;
> +       /*
> +        * Pad to fill implicit padding and provide space for future use.
> +        */
> +       __u32 padding[5];
> +       struct gpioline_config_attribute attrs[GPIOLINE_NUM_ATTRS_MAX];
> +};
> +
> +/**
> + * struct gpioline_request - Information about a request for GPIO lines
> + * @offsets: an array of desired lines, specified by offset index for the
> + * associated GPIO device
> + * @consumer: a desired consumer label for the selected GPIO lines such as
> + * "my-bitbanged-relay"
> + * @config: requested configuration for the lines.
> + * @num_lines: number of lines requested in this request, i.e. the number
> + * of valid fields in the GPIOLINES_MAX sized arrays, set to 1 to request a
> + * single line
> + * @event_buffer_size: a suggested minimum number of line events that the
> + * kernel should buffer.  This is only relevant if edge detection is
> + * enabled in the configuration. Note that this is only a suggested value
> + * and the kernel may allocate a larger buffer or cap the size of the
> + * buffer. If this field is zero then the buffer size defaults to a minimum
> + * of num_lines*16.
> + * @padding: reserved for future use and must be zero filled
> + * @fd: if successful this field will contain a valid anonymous file handle
> + * after a GPIO_GET_LINE_IOCTL operation, zero or negative value means
> + * error
> + */
> +struct gpioline_request {
> +       __u32 offsets[GPIOLINES_MAX];
> +       char consumer[GPIO_MAX_NAME_SIZE];
> +       struct gpioline_config config;
> +       __u32 num_lines;
> +       __u32 event_buffer_size;
> +       /*
> +        * Pad struct to 64-bit boundary and provide space for future use.
> +        */
> +       __u32 padding[5];
> +       __s32 fd;
> +};
> +
> +/**
> + * struct gpioline_info_v2 - Information about a certain GPIO line
> + * @name: the name of this GPIO line, such as the output pin of the line on
> + * the chip, a rail or a pin header name on a board, as specified by the
> + * gpio chip, may be empty
> + * @consumer: a functional name for the consumer of this GPIO line as set
> + * by whatever is using it, will be empty if there is no current user but
> + * may also be empty if the consumer doesn't set this up
> + * @flags: flags for the GPIO line, such as GPIOLINE_FLAG_V2_ACTIVE_LOW,
> + * GPIOLINE_FLAG_V2_OUTPUT etc, OR:ed together
> + * @offset: the local offset on this GPIO device, fill this in when
> + * requesting the line information from the kernel
> + * @num_attrs: the number of attributes in attrs
> + * @attrs: the configuration attributes associated with the line.
> + * @padding: reserved for future use
> + */
> +struct gpioline_info_v2 {
> +       char name[GPIO_MAX_NAME_SIZE];
> +       char consumer[GPIO_MAX_NAME_SIZE];
> +       __u32 offset;
> +       __u32 num_attrs;
> +       __u64 flags;
> +       struct gpioline_attribute attrs[GPIOLINE_NUM_ATTRS_MAX];
> +       /*
> +        * Pad struct to 64-bit boundary and provide space for future use.
> +        */
> +       __u32 padding[4];
> +};
> +
> +enum gpioline_changed_type {
> +       GPIOLINE_CHANGED_REQUESTED      = 1,
> +       GPIOLINE_CHANGED_RELEASED       = 2,
> +       GPIOLINE_CHANGED_CONFIG         = 3,
> +};
> +
> +/**
> + * struct gpioline_info_changed_v2 - Information about a change in status
> + * of a GPIO line
> + * @info: updated line information
> + * @timestamp: estimate of time of status change occurrence, in nanoseconds
> + * @event_type: the type of change with a value from enum gpioline_changed_type
> + * @padding: reserved for future use
> + */
> +struct gpioline_info_changed_v2 {
> +       struct gpioline_info_v2 info;
> +       __u64 timestamp;
> +       __u32 event_type;
> +       /*
> +        * Pad struct to 64-bit boundary and provide space for future use.
> +        */
> +       __u32 padding[5];
> +};
> +
> +enum gpioline_event_id {
> +       GPIOLINE_EVENT_RISING_EDGE      = 1,
> +       GPIOLINE_EVENT_FALLING_EDGE     = 2,
> +};
> +
> +/**
> + * struct gpioline_event - The actual event being pushed to userspace
> + * @timestamp: best estimate of time of event occurrence, in nanoseconds.
> + * The timestamp is read from CLOCK_MONOTONIC and is intended to allow the
> + * accurate measurement of the time between events.  It does not provide
> + * the wall-clock time.
> + * @id: event identifier with value from enum gpioline_event_id
> + * @offset: the offset of the line that triggered the event
> + * @seqno: the sequence number for this event in the sequence of events for
> + * all the lines in this line request
> + * @line_seqno: the sequence number for this event in the sequence of
> + * events on this particular line
> + * @padding: reserved for future use
> + */
> +struct gpioline_event {
> +       __u64 timestamp;
> +       __u32 id;
> +       __u32 offset;
> +       __u32 seqno;
> +       __u32 line_seqno;
> +       /*
> +        * Pad struct to 64-bit boundary and provide space for future use.
> +        */
> +       __u32 padding[6];
> +};
> +
> +/*
> + *  ABI v1
> + */
> +
>  /* Informational flags */
>  #define GPIOLINE_FLAG_KERNEL           (1UL << 0) /* Line used by the kernel */
>  #define GPIOLINE_FLAG_IS_OUT           (1UL << 1)
> @@ -64,13 +312,6 @@ struct gpioline_info {
>  /* Maximum number of requested handles */
>  #define GPIOHANDLES_MAX 64
>
> -/* Possible line status change events */
> -enum {
> -       GPIOLINE_CHANGED_REQUESTED = 1,
> -       GPIOLINE_CHANGED_RELEASED,
> -       GPIOLINE_CHANGED_CONFIG,
> -};
> -
>  /**
>   * struct gpioline_info_changed - Information about a change in status
>   * of a GPIO line
> @@ -149,8 +390,6 @@ struct gpiohandle_config {
>         __u32 padding[4]; /* padding for future use */
>  };
>
> -#define GPIOHANDLE_SET_CONFIG_IOCTL _IOWR(0xB4, 0x0a, struct gpiohandle_config)
> -
>  /**
>   * struct gpiohandle_data - Information of values on a GPIO handle
>   * @values: when getting the state of lines this contains the current
> @@ -161,9 +400,6 @@ struct gpiohandle_data {
>         __u8 values[GPIOHANDLES_MAX];
>  };
>
> -#define GPIOHANDLE_GET_LINE_VALUES_IOCTL _IOWR(0xB4, 0x08, struct gpiohandle_data)
> -#define GPIOHANDLE_SET_LINE_VALUES_IOCTL _IOWR(0xB4, 0x09, struct gpiohandle_data)
> -
>  /* Eventrequest flags */
>  #define GPIOEVENT_REQUEST_RISING_EDGE  (1UL << 0)
>  #define GPIOEVENT_REQUEST_FALLING_EDGE (1UL << 1)
> @@ -207,11 +443,31 @@ struct gpioevent_data {
>         __u32 id;
>  };
>
> +/*
> + * v1 and v2 ioctl()s
> + */
>  #define GPIO_GET_CHIPINFO_IOCTL _IOR(0xB4, 0x01, struct gpiochip_info)
> +#define GPIO_GET_LINEINFO_UNWATCH_IOCTL _IOWR(0xB4, 0x0C, __u32)
> +
> +/*
> + * v2 ioctl()s
> + */
> +#define GPIO_GET_LINEINFO_V2_IOCTL _IOWR(0xB4, 0x05, struct gpioline_info_v2)
> +#define GPIO_GET_LINEINFO_WATCH_V2_IOCTL _IOWR(0xB4, 0x06, struct gpioline_info_v2)
> +#define GPIO_GET_LINE_IOCTL _IOWR(0xB4, 0x07, struct gpioline_request)
> +#define GPIOLINE_SET_CONFIG_IOCTL _IOWR(0xB4, 0x0D, struct gpioline_config)
> +#define GPIOLINE_GET_VALUES_IOCTL _IOWR(0xB4, 0x0E, struct gpioline_values)
> +#define GPIOLINE_SET_VALUES_IOCTL _IOWR(0xB4, 0x0F, struct gpioline_set_values)
> +
> +/*
> + * v1 ioctl()s
> + */
>  #define GPIO_GET_LINEINFO_IOCTL _IOWR(0xB4, 0x02, struct gpioline_info)
> -#define GPIO_GET_LINEINFO_WATCH_IOCTL _IOWR(0xB4, 0x0b, struct gpioline_info)
> -#define GPIO_GET_LINEINFO_UNWATCH_IOCTL _IOWR(0xB4, 0x0c, __u32)
>  #define GPIO_GET_LINEHANDLE_IOCTL _IOWR(0xB4, 0x03, struct gpiohandle_request)
>  #define GPIO_GET_LINEEVENT_IOCTL _IOWR(0xB4, 0x04, struct gpioevent_request)
> +#define GPIOHANDLE_GET_LINE_VALUES_IOCTL _IOWR(0xB4, 0x08, struct gpiohandle_data)
> +#define GPIOHANDLE_SET_LINE_VALUES_IOCTL _IOWR(0xB4, 0x09, struct gpiohandle_data)
> +#define GPIOHANDLE_SET_CONFIG_IOCTL _IOWR(0xB4, 0x0A, struct gpiohandle_config)
> +#define GPIO_GET_LINEINFO_WATCH_IOCTL _IOWR(0xB4, 0x0B, struct gpioline_info)
>
>  #endif /* _UAPI_GPIO_H_ */
> --
> 2.27.0
>

Everything else looks good to me. Much cleaner and more elegant than
v1. Great job!

I may come up with something else while browsing other patches I suppose.

Bartosz

On Tue, Aug 04, 2020 at 07:42:34PM +0200, Bartosz Golaszewski wrote:
> On Sat, Jul 25, 2020 at 6:20 AM Kent Gibson <warthog618@gmail.com> wrote:
> >
> > Add a new version of the uAPI to address existing 32/64-bit alignment
> > issues, add support for debounce and event sequence numbers, and provide
> > some future proofing by adding padding reserved for future use.
> >
> > The alignment issue relates to the gpioevent_data, which packs to different
> > sizes on 32-bit and 64-bit platforms. That creates problems for 32-bit apps
> > running on 64-bit kernels.  The patch addresses that particular issue, and
> > the problem more generally, by adding pad fields that explicitly pad
> > structs out to 64-bit boundaries, so they will pack to the same size now,
> > and even if some of the reserved padding is used for __u64 fields in the
> > future.
> >
> > The lack of future proofing in v1 makes it impossible to, for example,
> > add the debounce feature that is included in v2.
> > The future proofing is addressed by providing reserved padding in all
> > structs for future features.  Specifically, the line request,
> > config, info, info_changed and event structs receive updated versions,
> > and the first three new ioctls.
> >
> > Signed-off-by: Kent Gibson <warthog618@gmail.com>
> > ---
> 
> Hi Kent,
> 
> Thanks a lot for your work on this. Please see comments below.
> 
> One thing I'd change globally for better readability is to have all
> new symbols marked as v2 - even if they have no counterparts in v1. I
> know libgpiod will wrap it all anyway but I think it's still a good
> way to make our work in user-space easier.
> 

Fair enough.  Oh joy.

> >
> > I haven't added any padding to gpiochip_info, as I haven't seen any calls
> > for new features for the corresponding ioctl, but I'm open to updating that
> > as well.
> >
> > As the majority of the structs and ioctls were being replaced, it seemed
> > opportune to rework some of the other aspects of the uAPI.
> >
> > Firstly, I've reworked the flags field throughout.  v1 has three different
> > flags fields, each with their own separate bit definitions.  In v2 that is
> > collapsed to one.
> >
> > I've also merged the handle and event requests into a single request, the
> > line request, as the two requests were mostly the same, other than the
> > edge detection provided by event requests.  As a byproduct, the v2 uAPI
> > allows for multiple lines producing edge events on the same line handle.
> > This is a new capability as v1 only supports a single line in an event
> > request.
> >
> > This means there are now only two types of file handle to be concerned with,
> > the chip and the line, and it is clearer which ioctls apply to which type
> > of handle.
> >
> > There is also some minor renaming of fields for consistency compared to
> > their v1 counterparts, e.g. offset rather than lineoffset or line_offset,
> > and consumer rather than consumer_label.
> >
> > Additionally, v1 GPIOHANDLES_MAX becomes GPIOLINES_MAX in v2 for clarity,
> > and the gpiohandle_data __u8 array becomes a bitmap gpioline_values.
> >
> > The v2 uAPI is mostly just a reorganisation of v1, so userspace code,
> > particularly libgpiod, should easily port to it.
> >
> 
> I think the info above is worth putting into the commit message.
> Especially the part about merging the two event types.
> 

OK, but I'll rework it a bit to make it more suitable for a commit
message.

> > Changes since v1:
> >  - lower case V1 and V2, except in capitalized names
> >  - hyphenate 32/64-bit
> >  - rename bitmap field to bits
> >  - drop PAD_SIZE consts in favour of hard coded numbers
> >  - sort includes
> >  - change config flags to __u64
> >  - increase padding of gpioline_event
> >  - relocate GPIOLINE_CHANGED enum into v2 section (is common with v1)
> >  - rework config to collapse direction, drive, bias and edge enums back
> >    into flags and add optional attributes that can be associated with a
> >    subset of the requested lines.
> >
> > Changes since the RFC:
> >  - document the constraints on array sizes to maintain 32/64 alignment
> >  - add sequence numbers to gpioline_event
> >  - use bitmap for values instead of array of __u8
> >  - gpioline_info_v2 contains gpioline_config instead of its composite fields
> >  - provide constants for all array sizes, especially padding
> >  - renamed "GPIOLINE_FLAG_V2_KERNEL" to "GPIOLINE_FLAG_V2_USED"
> >  - renamed "default_values" to "values"
> >  - made gpioline_direction zero based
> >  - document clock used in gpioline_event timestamp
> >  - add event_buffer_size to gpioline_request
> >  - rename debounce to debounce_period
> >  - rename lines to num_lines
> >
> >  include/uapi/linux/gpio.h | 284 ++++++++++++++++++++++++++++++++++++--
> >  1 file changed, 270 insertions(+), 14 deletions(-)
> >
> > diff --git a/include/uapi/linux/gpio.h b/include/uapi/linux/gpio.h
> > index 285cc10355b2..3f6db33014f0 100644
> > --- a/include/uapi/linux/gpio.h
> > +++ b/include/uapi/linux/gpio.h
> > @@ -12,10 +12,13 @@
> >  #define _UAPI_GPIO_H_
> >
> >  #include <linux/ioctl.h>
> > +#include <linux/kernel.h>
> >  #include <linux/types.h>
> >
> >  /*
> >   * The maximum size of name and label arrays.
> > + *
> > + * Must be a multiple of 8 to ensure 32/64-bit alignment of structs.
> >   */
> >  #define GPIO_MAX_NAME_SIZE 32
> >
> > @@ -32,6 +35,251 @@ struct gpiochip_info {
> >         __u32 lines;
> >  };
> >
> > +/*
> > + * Maximum number of requested lines.
> > + *
> > + * Must be a multiple of 8 to ensure 32/64-bit alignment of structs.
> > + */
> > +#define GPIOLINES_MAX 64
> > +
> > +/* The number of __u64 required for a bitmap for GPIOLINES_MAX lines */
> > +#define GPIOLINES_BITMAP_SIZE  __KERNEL_DIV_ROUND_UP(GPIOLINES_MAX, 64)
> > +
> 
> In what circumstances can this be different than 1? It's worth
> documenting here I suppose.
> 

In terms of the API definition, GPIOLINES_MAX can be anything you want
and the definitions are still valid.  In practice in the mainline kernel
it would always be 1 for ABI compatibility.

Chiselling GPIOLINES_MAX <= 64 into stone could simplify things a bit,
as all the bitmaps reduce to a single __u64.  Would you prefer that?

> > +/*
> > + * The maximum number of configuration attributes associated with a line
> > + * request.
> > + */
> > +#define GPIOLINE_NUM_ATTRS_MAX 10
> > +
> 
> How did you choose this number? I mean: it's reasonable - just asking
> for clarification.
> 

I didn't want to constrain the possible configurations by making it too
small, particularly allowing for future attributes, but wanted to keep the
request size down so it can still comfortably fit on the stack.
The gpioline_request stands at 592 bytes, which is already substantially
larger than the 364 bytes of the v1 request, and each additional config
attribute slot adds another 24 bytes.

So 10 seemed like a happy medium.

> > +/**
> > + * enum gpioline_flag_v2 - &struct gpioline_attribute.flags values
> > + */
> > +enum gpioline_flag_v2 {
> > +       GPIOLINE_FLAG_V2_USED                   = 1UL << 0, /* line is not available for request */
> > +       GPIOLINE_FLAG_V2_ACTIVE_LOW             = 1UL << 1,
> > +       GPIOLINE_FLAG_V2_INPUT                  = 1UL << 2,
> > +       GPIOLINE_FLAG_V2_OUTPUT                 = 1UL << 3,
> > +       GPIOLINE_FLAG_V2_EDGE_RISING            = 1UL << 4,
> > +       GPIOLINE_FLAG_V2_EDGE_FALLING           = 1UL << 5,
> > +       GPIOLINE_FLAG_V2_OPEN_DRAIN             = 1UL << 6,
> > +       GPIOLINE_FLAG_V2_OPEN_SOURCE            = 1UL << 7,
> > +       GPIOLINE_FLAG_V2_BIAS_PULL_UP           = 1UL << 8,
> > +       GPIOLINE_FLAG_V2_BIAS_PULL_DOWN         = 1UL << 9,
> > +       GPIOLINE_FLAG_V2_BIAS_DISABLED          = 1UL << 10,
> > +};
> > +
> > +/**
> > + * struct gpioline_values - Values of GPIO lines
> > + * @bits: a bitmap containing the value of the lines, set to 1 for active
> > + * and 0 for inactive.  Note that this is the logical value, which will be
> > + * the opposite of the physical value if the line is configured as active
> > + * low.
> > + */
> > +struct gpioline_values {
> > +       __u64 bits[GPIOLINES_BITMAP_SIZE];
> > +};
> > +
> 
> We can set values only for a subset of requested lines but AFAICT we
> can't read values of only a subset of lines. Would it be difficult to
> remove this limitation? While reading values always succeeds - even if
> the line is in input mode and has edge detected - I think that someone
> may want to request the max number of lines without reading all their
> values each time. Maybe consider merging this with struct
> gpioline_set_values?
> 

That is correct.

I considered that corner case to be unlikely, as a major point of
requesting lines together is to be able to perform collective operations
on them as atomically as possible.  If you only want subsets then
request them as separate subsets.

Do you have a case in mind where you would have overlapping subsets?

Not difficult to remove the limitation - I just didn't see sufficient
benefit. 

> > +/**
> > + * struct gpioline_set_values - Values to set a group of GPIO lines
> > + * @mask: a bitmap identifying the lines to set.
> > + * @bits: a bitmap containing the value of the lines, set to 1 for active
> > + * and 0 for inactive.  Note that this is the logical value, which will be
> > + * the opposite of the physical value if the line is configured as active
> > + * low.
> > + */
> > +struct gpioline_set_values {
> > +       __u64 mask[GPIOLINES_BITMAP_SIZE];
> > +       __u64 bits[GPIOLINES_BITMAP_SIZE];
> > +};
> > +
> > +/**
> > + * enum gpioline_attr_id - &struct gpioline_attribute.id values
> > + */
> > +enum gpioline_attr_id {
> > +       GPIOLINE_ATTR_ID_FLAGS                  = 1,
> > +       GPIOLINE_ATTR_ID_OUTPUT_VALUES          = 2,
> > +       GPIOLINE_ATTR_ID_DEBOUNCE               = 3,
> > +};
> > +
> > +/**
> > + * struct gpioline_attribute - a configurable attribute of a line
> > + * @id: attribute identifier with value from &enum gpioline_attr_id
> > + * @padding: reserved for future use and must be zero filled
> > + * @flags: if id is GPIOLINE_ATTR_ID_FLAGS, the flags for the GPIO line,
> > + * with values from enum gpioline_flag_v2, such as
> > + * GPIOLINE_FLAG_V2_ACTIVE_LOW, GPIOLINE_FLAG_V2_OUTPUT etc, OR:ed
> > + * together.  This overrides the default flags contained in the &struct
> > + * gpioline_config for the associated line.
> > + * @values: if id is GPIOLINE_ATTR_ID_OUTPUT_VALUES, the values to which
> > + * the lines will be set
> > + * @debounce_period: if id is GPIOLINE_ATTR_ID_DEBOUNCE, the desired
> > + * debounce period, in microseconds
> > + */
> > +struct gpioline_attribute {
> > +       __u32 id;
> > +       __u32 padding;
> > +       union {
> > +               __u64 flags;
> > +               struct gpioline_values values;
> > +               __u32 debounce_period;
> > +       };
> > +};
> 
> I'm afraid that if we don't have enough padding here (at the end),
> we'll end up wanting to add a new attribute at some point whose
> argument won't fit. Maybe have a specific field in the union that's
> even larger than __u64?
> 

I'm satisfied with the 64-bit value restriction.

I don't want to go adding another 8 bytes of pad per attribute on the
off chance that we ever find such an attribute, and that we couldn't
find some other solution like using the __u32 padding, or user the
gpioline_config padding, or split it over two attributes....

> > +
> > +/**
> > + * struct gpioline_config_attribute - a configuration attribute associated
> > + * with one or more of the requested lines.
> > + * @mask: a bitmap identifying the lines to which the attribute applies
> > + * @attr: the configurable attribute
> > + */
> > +struct gpioline_config_attribute {
> > +       __u64 mask[GPIOLINES_BITMAP_SIZE];
> > +       struct gpioline_attribute attr;
> > +};
> > +
> > +/**
> > + * struct gpioline_config - Configuration for GPIO lines
> > + * @flags: flags for the GPIO lines, with values from enum
> > + * gpioline_flag_v2, such as GPIOLINE_FLAG_V2_ACTIVE_LOW,
> > + * GPIOLINE_FLAG_V2_OUTPUT etc, OR:ed together.  This is the default for
> > + * all requested lines but may be overridden for particular lines using
> > + * attrs.
> 
> So I'm having a hard time with this. I understand that the thinking
> behind it was: use the flags field to set all lines to INPUT by
> default and only set certain lines to OUTPUT with attrs. This would
> make life easier for user-space but it complicates the kernel code and
> I also believe that any such simplification should be handled by
> user-space libraries, not be exposed by kernel uAPI. My personal
> preference would be to drop the flags field and only handle attributes
> (maybe even define a special macro to set all bits in mask -
> GPIOLINE_CONFIG_ALL_LINES or something) on a first-in-wins basis. I'm
> open to other suggestions though.
> 

I think I've addressed this elsewhere, and still think it is worthwhile
and very low cost.  I thought it was an easy win when I added it, and
still do.

Happy to change the attrs to first-in-wins though - the validation of
the attrs is still my biggest bugbear with this version.

Cheers,
Kent.

On Wed, Aug 5, 2020 at 7:19 AM Kent Gibson <warthog618@gmail.com> wrote:
>

[snip]

> > >
> > > +/*
> > > + * Maximum number of requested lines.
> > > + *
> > > + * Must be a multiple of 8 to ensure 32/64-bit alignment of structs.
> > > + */
> > > +#define GPIOLINES_MAX 64
> > > +
> > > +/* The number of __u64 required for a bitmap for GPIOLINES_MAX lines */
> > > +#define GPIOLINES_BITMAP_SIZE  __KERNEL_DIV_ROUND_UP(GPIOLINES_MAX, 64)
> > > +
> >
> > In what circumstances can this be different than 1? It's worth
> > documenting here I suppose.
> >
>
> In terms of the API definition, GPIOLINES_MAX can be anything you want
> and the definitions are still valid.  In practice in the mainline kernel
> it would always be 1 for ABI compatibility.
>
> Chiselling GPIOLINES_MAX <= 64 into stone could simplify things a bit,
> as all the bitmaps reduce to a single __u64.  Would you prefer that?
>

I'm not sure I follow. We need to chisel some max value in stone. Up
to that point it's been 64. We can make it more and the bitmap API
would handle it alright but if we don't, then this
__KERNEL_DIV_ROUND_UP() is unnecessary. Limiting it to 64 makes things
very simple thanks to fitting into a __u64 though. I've personally
never needed to request even half that so I guess this value's fine?

> > > +/*
> > > + * The maximum number of configuration attributes associated with a line
> > > + * request.
> > > + */
> > > +#define GPIOLINE_NUM_ATTRS_MAX 10
> > > +
> >
> > How did you choose this number? I mean: it's reasonable - just asking
> > for clarification.
> >
>
> I didn't want to constrain the possible configurations by making it too
> small, particularly allowing for future attributes, but wanted to keep the
> request size down so it can still comfortably fit on the stack.
> The gpioline_request stands at 592 bytes, which is already substantially
> larger than the 364 bytes of the v1 request, and each additional config
> attribute slot adds another 24 bytes.
>
> So 10 seemed like a happy medium.
>

Makes sense.

> > > +/**
> > > + * enum gpioline_flag_v2 - &struct gpioline_attribute.flags values
> > > + */
> > > +enum gpioline_flag_v2 {
> > > +       GPIOLINE_FLAG_V2_USED                   = 1UL << 0, /* line is not available for request */
> > > +       GPIOLINE_FLAG_V2_ACTIVE_LOW             = 1UL << 1,
> > > +       GPIOLINE_FLAG_V2_INPUT                  = 1UL << 2,
> > > +       GPIOLINE_FLAG_V2_OUTPUT                 = 1UL << 3,
> > > +       GPIOLINE_FLAG_V2_EDGE_RISING            = 1UL << 4,
> > > +       GPIOLINE_FLAG_V2_EDGE_FALLING           = 1UL << 5,
> > > +       GPIOLINE_FLAG_V2_OPEN_DRAIN             = 1UL << 6,
> > > +       GPIOLINE_FLAG_V2_OPEN_SOURCE            = 1UL << 7,
> > > +       GPIOLINE_FLAG_V2_BIAS_PULL_UP           = 1UL << 8,
> > > +       GPIOLINE_FLAG_V2_BIAS_PULL_DOWN         = 1UL << 9,
> > > +       GPIOLINE_FLAG_V2_BIAS_DISABLED          = 1UL << 10,
> > > +};
> > > +
> > > +/**
> > > + * struct gpioline_values - Values of GPIO lines
> > > + * @bits: a bitmap containing the value of the lines, set to 1 for active
> > > + * and 0 for inactive.  Note that this is the logical value, which will be
> > > + * the opposite of the physical value if the line is configured as active
> > > + * low.
> > > + */
> > > +struct gpioline_values {
> > > +       __u64 bits[GPIOLINES_BITMAP_SIZE];
> > > +};
> > > +
> >
> > We can set values only for a subset of requested lines but AFAICT we
> > can't read values of only a subset of lines. Would it be difficult to
> > remove this limitation? While reading values always succeeds - even if
> > the line is in input mode and has edge detected - I think that someone
> > may want to request the max number of lines without reading all their
> > values each time. Maybe consider merging this with struct
> > gpioline_set_values?
> >
>
> That is correct.
>
> I considered that corner case to be unlikely, as a major point of
> requesting lines together is to be able to perform collective operations
> on them as atomically as possible.  If you only want subsets then
> request them as separate subsets.
>

And yet this version implements heterogeneous config and setting edge
detection and values of subsets of requested lines. :)

> Do you have a case in mind where you would have overlapping subsets?
>

No, not really but then I also don't have a use-case for setting only
a certain subset of lines.

> Not difficult to remove the limitation - I just didn't see sufficient
> benefit.
>

Using the same structure for setting and getting values is a benefit
IMO. If it's not a difficult task, then I think it's worth adding it.

> > > +/**
> > > + * struct gpioline_set_values - Values to set a group of GPIO lines
> > > + * @mask: a bitmap identifying the lines to set.
> > > + * @bits: a bitmap containing the value of the lines, set to 1 for active
> > > + * and 0 for inactive.  Note that this is the logical value, which will be
> > > + * the opposite of the physical value if the line is configured as active
> > > + * low.
> > > + */
> > > +struct gpioline_set_values {
> > > +       __u64 mask[GPIOLINES_BITMAP_SIZE];
> > > +       __u64 bits[GPIOLINES_BITMAP_SIZE];
> > > +};
> > > +
> > > +/**
> > > + * enum gpioline_attr_id - &struct gpioline_attribute.id values
> > > + */
> > > +enum gpioline_attr_id {
> > > +       GPIOLINE_ATTR_ID_FLAGS                  = 1,
> > > +       GPIOLINE_ATTR_ID_OUTPUT_VALUES          = 2,
> > > +       GPIOLINE_ATTR_ID_DEBOUNCE               = 3,
> > > +};
> > > +
> > > +/**
> > > + * struct gpioline_attribute - a configurable attribute of a line
> > > + * @id: attribute identifier with value from &enum gpioline_attr_id
> > > + * @padding: reserved for future use and must be zero filled
> > > + * @flags: if id is GPIOLINE_ATTR_ID_FLAGS, the flags for the GPIO line,
> > > + * with values from enum gpioline_flag_v2, such as
> > > + * GPIOLINE_FLAG_V2_ACTIVE_LOW, GPIOLINE_FLAG_V2_OUTPUT etc, OR:ed
> > > + * together.  This overrides the default flags contained in the &struct
> > > + * gpioline_config for the associated line.
> > > + * @values: if id is GPIOLINE_ATTR_ID_OUTPUT_VALUES, the values to which
> > > + * the lines will be set
> > > + * @debounce_period: if id is GPIOLINE_ATTR_ID_DEBOUNCE, the desired
> > > + * debounce period, in microseconds
> > > + */
> > > +struct gpioline_attribute {
> > > +       __u32 id;
> > > +       __u32 padding;
> > > +       union {
> > > +               __u64 flags;
> > > +               struct gpioline_values values;
> > > +               __u32 debounce_period;
> > > +       };
> > > +};
> >
> > I'm afraid that if we don't have enough padding here (at the end),
> > we'll end up wanting to add a new attribute at some point whose
> > argument won't fit. Maybe have a specific field in the union that's
> > even larger than __u64?
> >
>
> I'm satisfied with the 64-bit value restriction.
>
> I don't want to go adding another 8 bytes of pad per attribute on the
> off chance that we ever find such an attribute, and that we couldn't
> find some other solution like using the __u32 padding, or user the
> gpioline_config padding, or split it over two attributes....
>

Fair enough.

> > > +
> > > +/**
> > > + * struct gpioline_config_attribute - a configuration attribute associated
> > > + * with one or more of the requested lines.
> > > + * @mask: a bitmap identifying the lines to which the attribute applies
> > > + * @attr: the configurable attribute
> > > + */
> > > +struct gpioline_config_attribute {
> > > +       __u64 mask[GPIOLINES_BITMAP_SIZE];
> > > +       struct gpioline_attribute attr;
> > > +};
> > > +
> > > +/**
> > > + * struct gpioline_config - Configuration for GPIO lines
> > > + * @flags: flags for the GPIO lines, with values from enum
> > > + * gpioline_flag_v2, such as GPIOLINE_FLAG_V2_ACTIVE_LOW,
> > > + * GPIOLINE_FLAG_V2_OUTPUT etc, OR:ed together.  This is the default for
> > > + * all requested lines but may be overridden for particular lines using
> > > + * attrs.
> >
> > So I'm having a hard time with this. I understand that the thinking
> > behind it was: use the flags field to set all lines to INPUT by
> > default and only set certain lines to OUTPUT with attrs. This would
> > make life easier for user-space but it complicates the kernel code and
> > I also believe that any such simplification should be handled by
> > user-space libraries, not be exposed by kernel uAPI. My personal
> > preference would be to drop the flags field and only handle attributes
> > (maybe even define a special macro to set all bits in mask -
> > GPIOLINE_CONFIG_ALL_LINES or something) on a first-in-wins basis. I'm
> > open to other suggestions though.
> >
>
> I think I've addressed this elsewhere, and still think it is worthwhile
> and very low cost.  I thought it was an easy win when I added it, and
> still do.
>
> Happy to change the attrs to first-in-wins though - the validation of
> the attrs is still my biggest bugbear with this version.

Yes, I read your other reply. Ok, makes sense to have default flags
with an attribute for overrides. This just needs very explicit
documentation.

Bartosz

On Wed, Aug 05, 2020 at 07:47:57PM +0200, Bartosz Golaszewski wrote:
> On Wed, Aug 5, 2020 at 7:19 AM Kent Gibson <warthog618@gmail.com> wrote:
> >
> 
> [snip]
> 
> > > >
> > > > +/*
> > > > + * Maximum number of requested lines.
> > > > + *
> > > > + * Must be a multiple of 8 to ensure 32/64-bit alignment of structs.
> > > > + */
> > > > +#define GPIOLINES_MAX 64
> > > > +
> > > > +/* The number of __u64 required for a bitmap for GPIOLINES_MAX lines */
> > > > +#define GPIOLINES_BITMAP_SIZE  __KERNEL_DIV_ROUND_UP(GPIOLINES_MAX, 64)
> > > > +
> > >
> > > In what circumstances can this be different than 1? It's worth
> > > documenting here I suppose.
> > >
> >
> > In terms of the API definition, GPIOLINES_MAX can be anything you want
> > and the definitions are still valid.  In practice in the mainline kernel
> > it would always be 1 for ABI compatibility.
> >
> > Chiselling GPIOLINES_MAX <= 64 into stone could simplify things a bit,
> > as all the bitmaps reduce to a single __u64.  Would you prefer that?
> >
> 
> I'm not sure I follow. We need to chisel some max value in stone. Up
> to that point it's been 64. We can make it more and the bitmap API
> would handle it alright but if we don't, then this
> __KERNEL_DIV_ROUND_UP() is unnecessary. Limiting it to 64 makes things
> very simple thanks to fitting into a __u64 though. I've personally
> never needed to request even half that so I guess this value's fine?
> 

By "chiselling in stone" I mean not supporting > 64 lines - even in
custom kernel builds.  The uAPI and definition and implementation would
lock that in.  As it stands a custom build could use > 64 and it should
all still work as the bitmaps would be resized.

I satisfied that 64 is more than enough for what this API is intended for,
so I'll change the bitmaps to a single __u64, and remove
GPIOLINES_BITMAP_SIZE.

[ snip]
> > > > +       __u64 bits[GPIOLINES_BITMAP_SIZE];
> > > > +};
> > > > +
> > >
> > > We can set values only for a subset of requested lines but AFAICT we
> > > can't read values of only a subset of lines. Would it be difficult to
> > > remove this limitation? While reading values always succeeds - even if
> > > the line is in input mode and has edge detected - I think that someone
> > > may want to request the max number of lines without reading all their
> > > values each time. Maybe consider merging this with struct
> > > gpioline_set_values?
> > >
> >
> > That is correct.
> >
> > I considered that corner case to be unlikely, as a major point of
> > requesting lines together is to be able to perform collective operations
> > on them as atomically as possible.  If you only want subsets then
> > request them as separate subsets.
> >
> 
> And yet this version implements heterogeneous config and setting edge
> detection and values of subsets of requested lines. :)
> 

The corner case I was referring to was only wanting to get a subset of
lines and caring that there may be a slight performance gain if the
kernel filters out the lines you aren't interested in :(.

> > Do you have a case in mind where you would have overlapping subsets?
> >
> 
> No, not really but then I also don't have a use-case for setting only
> a certain subset of lines.
> 
> > Not difficult to remove the limitation - I just didn't see sufficient
> > benefit.
> >
> 
> Using the same structure for setting and getting values is a benefit
> IMO. If it's not a difficult task, then I think it's worth adding it.
> 

OK, will add it in.

[ snip]
> > > (maybe even define a special macro to set all bits in mask -
> > > GPIOLINE_CONFIG_ALL_LINES or something) on a first-in-wins basis. I'm
> > > open to other suggestions though.
> > >
> >
> > I think I've addressed this elsewhere, and still think it is worthwhile
> > and very low cost.  I thought it was an easy win when I added it, and
> > still do.
> >
> > Happy to change the attrs to first-in-wins though - the validation of
> > the attrs is still my biggest bugbear with this version.
> 
> Yes, I read your other reply. Ok, makes sense to have default flags
> with an attribute for overrides. This just needs very explicit
> documentation.
> 

I'll add documentation that the attrs associations are on a
first-in-wins basis, and that subsequent associations are ignored.

Cheers,
Kent.

On Wed, Aug 05, 2020 at 01:18:53PM +0800, Kent Gibson wrote:
> On Tue, Aug 04, 2020 at 07:42:34PM +0200, Bartosz Golaszewski wrote:
> > On Sat, Jul 25, 2020 at 6:20 AM Kent Gibson <warthog618@gmail.com> wrote:

[snip]

> > > config, info, info_changed and event structs receive updated versions,
> > > and the first three new ioctls.
> > >
> > > Signed-off-by: Kent Gibson <warthog618@gmail.com>
> > > ---
> > 
> > Hi Kent,
> > 
> > Thanks a lot for your work on this. Please see comments below.
> > 
> > One thing I'd change globally for better readability is to have all
> > new symbols marked as v2 - even if they have no counterparts in v1. I
> > know libgpiod will wrap it all anyway but I think it's still a good
> > way to make our work in user-space easier.
> > 
> 
> Fair enough.  Oh joy.
> 

Given that the intent is to highlight that the symbols are related to the
v2 of the GPIO uAPI, and not the second version of a particular type, it
makes more sense to me that the v2 is placed adjacent to the GPIO in the
name.  e.g. gpioline_flag_v2 would become gpiov2line_flag.

Does that work for you?

Cheers,
Kent.

On Thu, Aug 6, 2020 at 3:15 AM Kent Gibson <warthog618@gmail.com> wrote:
>
> On Wed, Aug 05, 2020 at 01:18:53PM +0800, Kent Gibson wrote:
> > On Tue, Aug 04, 2020 at 07:42:34PM +0200, Bartosz Golaszewski wrote:
> > > On Sat, Jul 25, 2020 at 6:20 AM Kent Gibson <warthog618@gmail.com> wrote:
>
> [snip]
>
> > > > config, info, info_changed and event structs receive updated versions,
> > > > and the first three new ioctls.
> > > >
> > > > Signed-off-by: Kent Gibson <warthog618@gmail.com>
> > > > ---
> > >
> > > Hi Kent,
> > >
> > > Thanks a lot for your work on this. Please see comments below.
> > >
> > > One thing I'd change globally for better readability is to have all
> > > new symbols marked as v2 - even if they have no counterparts in v1. I
> > > know libgpiod will wrap it all anyway but I think it's still a good
> > > way to make our work in user-space easier.
> > >
> >
> > Fair enough.  Oh joy.
> >
>
> Given that the intent is to highlight that the symbols are related to the
> v2 of the GPIO uAPI, and not the second version of a particular type, it
> makes more sense to me that the v2 is placed adjacent to the GPIO in the
> name.  e.g. gpioline_flag_v2 would become gpiov2line_flag.
>
> Does that work for you?
>

Yes, except that gpiov2line is a terrible prefix. Perhaps we should
make that into gpiov2_line_flag and same for all others? Maybe even
gpio_v2_line_flag if that doesn't make the symbols too long/too hard
to read.

Bartosz