| Message ID | 1468880090-46076-1-git-send-email-davidhsu@google.com |
|---|---|
| State | Deferred |
| Headers | show |
On Mon, Jul 18, 2016 at 03:14:50PM -0700, David Hsu wrote: > Pwm channels don't send uevents when exported, this change adds the > channels to a pwm class and set their device type to pwm_channel so > uevents are sent. > > To do this properly, the device names need to change to uniquely > identify a channel. This change is from pwmN to pwmchipM:N > > Signed-off-by: David Hsu <davidhsu@google.com> > --- > v2: Use parent name instead of chip->base for channel naming. > > Documentation/pwm.txt | 6 ++++-- > drivers/pwm/sysfs.c | 18 +++++++++++++----- > 2 files changed, 17 insertions(+), 7 deletions(-) Sorry for taking so long to look at this. I had applied this to my tree and was doing some experiments when I noticed some oddities. > diff --git a/drivers/pwm/sysfs.c b/drivers/pwm/sysfs.c > index 01695d4..cb2b376 100644 > --- a/drivers/pwm/sysfs.c > +++ b/drivers/pwm/sysfs.c > @@ -23,6 +23,8 @@ > #include <linux/kdev_t.h> > #include <linux/pwm.h> > > +static struct class pwm_class; > + > struct pwm_export { > struct device child; > struct pwm_device *pwm; > @@ -222,6 +224,10 @@ static struct attribute *pwm_attrs[] = { > }; > ATTRIBUTE_GROUPS(pwm); > > +static const struct device_type pwm_channel_type = { > + .name = "pwm_channel", > +}; In order to do some tracing, I ended up implementing the ->uevent() callback of struct device_type. What I noticed when exporting a PWM is that that ->uevent() gets called recursively and the operation never finishes. I have no idea why that happens, though. > + > static void pwm_export_release(struct device *child) > { > struct pwm_export *export = child_to_pwm_export(child); > @@ -248,9 +254,11 @@ static int pwm_export_child(struct device *parent, struct pwm_device *pwm) > > export->child.release = pwm_export_release; > export->child.parent = parent; > + export->child.type = &pwm_channel_type; > export->child.devt = MKDEV(0, 0); > + export->child.class = &pwm_class; This particular change isn't going to work, unfortunately. Children of a PWM chip, i.e. PWM devices (or channels) are not the same as chips. The above, however, will cause the attributes associated with a PWM chip to be associated with each PWM device as well. For example it will cause a PWM device to expose an "export" attribute in userspace. Writing to that file will give you a nice oops, along these lines: [ 89.631855] Unable to handle kernel NULL pointer dereference at virtual address 00000014 [ 89.640146] pgd = c2b16700 [ 89.642879] [00000014] *pgd=82b74003, *pmd=f4dd8003 [ 89.647830] Internal error: Oops: 207 [#1] PREEMPT SMP ARM [ 89.653330] Modules linked in: nouveau tegra_drm ttm drm_kms_helper cfbfillrect syscopyarea cfbimgblt sysfillrect sysimgblt fb_sys_fops cfbcopyarea drm [ 89.667194] CPU: 3 PID: 284 Comm: sh Not tainted 4.8.0-rc3-next-20160825-00026-g7065511b7003-dirty #82 [ 89.676507] Hardware name: NVIDIA Tegra SoC (Flattened Device Tree) [ 89.682787] task: c2b39500 task.stack: c3034000 [ 89.687327] PC is at export_store+0x34/0x170 [ 89.691598] LR is at _kstrtoull+0x2c/0x70 [ 89.695607] pc : [<c04b1cb0>] lr : [<c048a0e4>] psr: 60000013 [ 89.695607] sp : c3035ea0 ip : c04b1c7c fp : bec8eb0c [ 89.707068] r10: ee1e9b8c r9 : c3035f80 r8 : 00000002 [ 89.712287] r7 : c2b70800 r6 : 00000000 r5 : ee1e9b80 r4 : 00000000 [ 89.718806] r3 : 00000000 r2 : 00000000 r1 : 00000000 r0 : 00000000 [ 89.725327] Flags: nZCv IRQs on FIQs on Mode SVC_32 ISA ARM Segment user [ 89.732453] Control: 30c5387d Table: 82b16700 DAC: 55555555 [ 89.738193] Process sh (pid: 284, stack limit = 0xc3034210) [ 89.743758] Stack: (0xc3035ea0 to 0xc3036000) [ 89.748116] 5ea0: ee1e9b8c 00000000 0014e408 00000002 ee1e9b80 00000000 00000000 ee19f180 [ 89.756286] 5ec0: c3035f80 c035fc98 00000000 00000000 c3070180 c035fbd8 0014e408 c3035f80 [ 89.764456] 5ee0: 00000000 00000002 00000000 c030167c 032cf000 c109bf44 c109bf44 c02f88b0 [ 89.772625] 5f00: ee8270c0 c02fac24 00000001 c3035f10 ef05c9e0 c0300fd8 c0327c08 c2b7b000 [ 89.780794] 5f20: 0000000a c2b7e000 c3184ec0 0000000a 00000400 c2b7e040 00000000 c3070180 [ 89.788964] 5f40: 00000002 0014e408 c3035f80 00000000 00000002 c0302464 00000001 0000000a [ 89.797132] 5f60: c2d076c0 c3070180 c3070180 00000000 00000000 0014e408 00000002 c03031b0 [ 89.805302] 5f80: 00000000 00000000 00000014 00000002 0014e408 b6e74d50 00000004 c02075e4 [ 89.813470] 5fa0: c3034000 c0207440 00000002 0014e408 00000001 0014e408 00000002 00000000 [ 89.821638] 5fc0: 00000002 0014e408 b6e74d50 00000004 00000002 00000004 b6f0e000 bec8eb0c [ 89.829808] 5fe0: 00000000 bec8ea64 b6d9ffa4 b6df970c 60000010 00000001 0b0a0908 0f0e0d0c [ 89.837996] [<c04b1cb0>] (export_store) from [<c035fc98>] (kernfs_fop_write+0xc0/0x1cc) [ 89.846005] [<c035fc98>] (kernfs_fop_write) from [<c030167c>] (__vfs_write+0x1c/0x114) [ 89.853940] [<c030167c>] (__vfs_write) from [<c0302464>] (vfs_write+0xa4/0x168) [ 89.861252] [<c0302464>] (vfs_write) from [<c03031b0>] (SyS_write+0x3c/0x90) [ 89.868304] [<c03031b0>] (SyS_write) from [<c0207440>] (ret_fast_syscall+0x0/0x34) [ 89.875883] Code: ebff6164 e2506000 ba000039 e59d1004 (e5943014) [ 89.882225] ---[ end trace 716eda7e65a4136a ]--- Given that we need a class associated with a device in order for it to generate uevents (why is that so, by the way?), I think we'd need to add a separate class implementation for PWM devices. That has the downside of adding yet another subdirectory to /sys/class, but I can't really think of another way of achieving what you need here. Greg, any ideas? Thierry
On Mon, Jul 18, 2016 at 03:14:50PM -0700, David Hsu wrote: > Pwm channels don't send uevents when exported, this change adds the > channels to a pwm class and set their device type to pwm_channel so > uevents are sent. > > To do this properly, the device names need to change to uniquely > identify a channel. This change is from pwmN to pwmchipM:N > > Signed-off-by: David Hsu <davidhsu@google.com> > --- > v2: Use parent name instead of chip->base for channel naming. > > Documentation/pwm.txt | 6 ++++-- > drivers/pwm/sysfs.c | 18 +++++++++++++----- > 2 files changed, 17 insertions(+), 7 deletions(-) Forgot to mention one other thing that had come to my mind... > diff --git a/drivers/pwm/sysfs.c b/drivers/pwm/sysfs.c [...] > @@ -248,9 +254,11 @@ static int pwm_export_child(struct device *parent, struct pwm_device *pwm) > > export->child.release = pwm_export_release; > export->child.parent = parent; > + export->child.type = &pwm_channel_type; > export->child.devt = MKDEV(0, 0); > + export->child.class = &pwm_class; > export->child.groups = pwm_groups; > - dev_set_name(&export->child, "pwm%u", pwm->hwpwm); > + dev_set_name(&export->child, "%s:%u", dev_name(parent), pwm->hwpwm); Using the colon as separator could possibly prevent the use of these files in paths lists. Consider the case where somebody wanted to give a list of PWM sysfs references: PWM_DEVICES=/sys/class/pwm/pwmchip0:0:/sys/class/pwm/pwmchip0:1 which might get parsed as four entries: - /sys/class/pwm/pwmchip0 - 0 - /sys/class/pwm/pwmchip0 - 1 none of which point to a valid PWM. There are a couple of other separators that might be possible, such as '-' or '.'. Then again, looking at existing usage in sysfs it seems like the colon is a fairly popular separator, so maybe I'm just being too paranoid. Thierry
diff --git a/Documentation/pwm.txt b/Documentation/pwm.txt index 789b27c..8453435 100644 --- a/Documentation/pwm.txt +++ b/Documentation/pwm.txt @@ -80,9 +80,11 @@ unexport - Unexports a PWM channel from sysfs (write-only). The PWM channels are numbered using a per-chip index from 0 to npwm-1. -When a PWM channel is exported a pwmX directory will be created in the +When a PWM channel is exported a pwmchipN:X directory will be created in the pwmchipN directory it is associated with, where X is the number of the -channel that was exported. The following properties will then be available: +channel that was exported. It will also be exposed at /sys/class/pwm/ and +can be identified by the pwm_channel device type. +The following properties will then be available: period - The total period of the PWM signal (read/write). Value is in nanoseconds and is the sum of the active and inactive diff --git a/drivers/pwm/sysfs.c b/drivers/pwm/sysfs.c index 01695d4..cb2b376 100644 --- a/drivers/pwm/sysfs.c +++ b/drivers/pwm/sysfs.c @@ -23,6 +23,8 @@ #include <linux/kdev_t.h> #include <linux/pwm.h> +static struct class pwm_class; + struct pwm_export { struct device child; struct pwm_device *pwm; @@ -222,6 +224,10 @@ static struct attribute *pwm_attrs[] = { }; ATTRIBUTE_GROUPS(pwm); +static const struct device_type pwm_channel_type = { + .name = "pwm_channel", +}; + static void pwm_export_release(struct device *child) { struct pwm_export *export = child_to_pwm_export(child); @@ -248,9 +254,11 @@ static int pwm_export_child(struct device *parent, struct pwm_device *pwm) export->child.release = pwm_export_release; export->child.parent = parent; + export->child.type = &pwm_channel_type; export->child.devt = MKDEV(0, 0); + export->child.class = &pwm_class; export->child.groups = pwm_groups; - dev_set_name(&export->child, "pwm%u", pwm->hwpwm); + dev_set_name(&export->child, "%s:%u", dev_name(parent), pwm->hwpwm); ret = device_register(&export->child); if (ret) { @@ -355,7 +363,6 @@ ATTRIBUTE_GROUPS(pwm_chip); static struct class pwm_class = { .name = "pwm", .owner = THIS_MODULE, - .dev_groups = pwm_chip_groups, }; static int pwmchip_sysfs_match(struct device *parent, const void *data) @@ -368,14 +375,15 @@ void pwmchip_sysfs_export(struct pwm_chip *chip) struct device *parent; /* - * If device_create() fails the pwm_chip is still usable by + * If device_create_with_groups() fails the pwm_chip is still usable by * the kernel its just not exported. */ - parent = device_create(&pwm_class, chip->dev, MKDEV(0, 0), chip, + parent = device_create_with_groups(&pwm_class, chip->dev, MKDEV(0, 0), + chip, pwm_chip_groups, "pwmchip%d", chip->base); if (IS_ERR(parent)) { dev_warn(chip->dev, - "device_create failed for pwm_chip sysfs export\n"); + "device_create_with_groups failed for pwm_chip sysfs export\n"); } }
Pwm channels don't send uevents when exported, this change adds the channels to a pwm class and set their device type to pwm_channel so uevents are sent. To do this properly, the device names need to change to uniquely identify a channel. This change is from pwmN to pwmchipM:N Signed-off-by: David Hsu <davidhsu@google.com> --- v2: Use parent name instead of chip->base for channel naming. Documentation/pwm.txt | 6 ++++-- drivers/pwm/sysfs.c | 18 +++++++++++++----- 2 files changed, 17 insertions(+), 7 deletions(-)