[v2,04/10] spi: Extend the core to ease integration of SPI memory controllers

Message ID 20180410224439.9260-5-boris.brezillon@bootlin.com
State Changes Requested
Headers show
Series
  • spi: Extend the framework to generically support memory devices
Related show

Commit Message

Boris Brezillon April 10, 2018, 10:44 p.m.
Some controllers are exposing high-level interfaces to access various
kind of SPI memories. Unfortunately they do not fit in the current
spi_controller model and usually have drivers placed in
drivers/mtd/spi-nor which are only supporting SPI NORs and not SPI
memories in general.

This is an attempt at defining a SPI memory interface which works for
all kinds of SPI memories (NORs, NANDs, SRAMs).

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
---
Changes in v2:
- Move all changes not directly related to spi_mem out of this commit
- Do not abuse ternary operation
- Reword a few comments and fix typos
- Do not make the default buswidth check in spi_mem_support_ops() if
  the controller implements this hook
- Make the addr value an u64 instead of an array of byte
- Move all spi-mem code/defs to separate header/source files and add a
  new Kconfig option to enable this interface
---
 drivers/spi/Kconfig         |   7 +
 drivers/spi/Makefile        |   1 +
 drivers/spi/spi-mem.c       | 408 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/spi/spi-mem.h | 249 +++++++++++++++++++++++++++
 include/linux/spi/spi.h     |   7 +
 5 files changed, 672 insertions(+)
 create mode 100644 drivers/spi/spi-mem.c
 create mode 100644 include/linux/spi/spi-mem.h

Comments

Vignesh R April 12, 2018, 2:38 p.m. | #1
Hi,

- Sourav Poddar <sourav.poddar@ti.com> mail ID no longer valid.

On Wednesday 11 April 2018 04:14 AM, Boris Brezillon wrote:
> Some controllers are exposing high-level interfaces to access various
> kind of SPI memories. Unfortunately they do not fit in the current
> spi_controller model and usually have drivers placed in
> drivers/mtd/spi-nor which are only supporting SPI NORs and not SPI
> memories in general.
> 
> This is an attempt at defining a SPI memory interface which works for
> all kinds of SPI memories (NORs, NANDs, SRAMs).
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
> ---

[...]

> +/**
> + * struct spi_mem_op - describes a SPI memory operation
> + * @cmd.buswidth: number of IO lines used to transmit the command
> + * @cmd.opcode: operation opcode
> + * @addr.nbytes: number of address bytes to send. Can be zero if the operation
> + *		 does not need to send an address
> + * @addr.buswidth: number of IO lines used to transmit the address cycles
> + * @addr.val: address value. This value is always sent MSB first on the bus.
> + *	      Note that only @addr.nbytes are taken into account in this
> + *	      address value, so users should make sure the value fits in the
> + *	      assigned number of bytes.
> + * @dummy.nbytes: number of dummy bytes to send after an opcode or address. Can
> + *		  be zero if the operation does not require dummy bytes
> + * @dummy.buswidth: number of IO lanes used to transmit the dummy bytes
> + * @data.buswidth: number of IO lanes used to send/receive the data
> + * @data.dir: direction of the transfer
> + * @data.buf.in: input buffer
> + * @data.buf.out: output buffer
> + */
> +struct spi_mem_op {
> +	struct {
> +		u8 buswidth;
> +		u8 opcode;
> +	} cmd;
> +
> +	struct {
> +		u8 nbytes;
> +		u8 buswidth;
> +		u64 val;

You could consider using loff_t here and be consistent with
spi_nor_read/write() API as well as mtd->_read().

> +	} addr;
> +
> +	struct {
> +		u8 nbytes;
> +		u8 buswidth;
> +	} dummy;
> +
> +	struct {
> +		u8 buswidth;
> +		enum spi_mem_data_dir dir;
> +		unsigned int nbytes;
> +		/* buf.{in,out} must be DMA-able. */
> +		union {
> +			void *in;
> +			const void *out;
> +		} buf;
> +	} data;
> +};
> +

Some flash devices support Dual/Quad DDR (Double Data Rate) mode and the
SPI controller driver would need to know this information. We will need
to add a field for that.

Currently, there are drivers under mtd/spi-nor/ that need to know
page/sector/total size of flash memory(info available in
-`struct spi_nor). We would need a way to provide this info to spi_mem
drivers, if we ever plan to move drivers under mtd/spi-nor to spi/


[...]
Boris Brezillon April 12, 2018, 3:10 p.m. | #2
On Thu, 12 Apr 2018 20:08:28 +0530
Vignesh R <vigneshr@ti.com> wrote:

> Hi,
> 
> - Sourav Poddar <sourav.poddar@ti.com> mail ID no longer valid.
> 
> On Wednesday 11 April 2018 04:14 AM, Boris Brezillon wrote:
> > Some controllers are exposing high-level interfaces to access various
> > kind of SPI memories. Unfortunately they do not fit in the current
> > spi_controller model and usually have drivers placed in
> > drivers/mtd/spi-nor which are only supporting SPI NORs and not SPI
> > memories in general.
> > 
> > This is an attempt at defining a SPI memory interface which works for
> > all kinds of SPI memories (NORs, NANDs, SRAMs).
> > 
> > Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
> > ---  
> 
> [...]
> 
> > +/**
> > + * struct spi_mem_op - describes a SPI memory operation
> > + * @cmd.buswidth: number of IO lines used to transmit the command
> > + * @cmd.opcode: operation opcode
> > + * @addr.nbytes: number of address bytes to send. Can be zero if the operation
> > + *		 does not need to send an address
> > + * @addr.buswidth: number of IO lines used to transmit the address cycles
> > + * @addr.val: address value. This value is always sent MSB first on the bus.
> > + *	      Note that only @addr.nbytes are taken into account in this
> > + *	      address value, so users should make sure the value fits in the
> > + *	      assigned number of bytes.
> > + * @dummy.nbytes: number of dummy bytes to send after an opcode or address. Can
> > + *		  be zero if the operation does not require dummy bytes
> > + * @dummy.buswidth: number of IO lanes used to transmit the dummy bytes
> > + * @data.buswidth: number of IO lanes used to send/receive the data
> > + * @data.dir: direction of the transfer
> > + * @data.buf.in: input buffer
> > + * @data.buf.out: output buffer
> > + */
> > +struct spi_mem_op {
> > +	struct {
> > +		u8 buswidth;
> > +		u8 opcode;
> > +	} cmd;
> > +
> > +	struct {
> > +		u8 nbytes;
> > +		u8 buswidth;
> > +		u64 val;  
> 
> You could consider using loff_t here and be consistent with
> spi_nor_read/write() API as well as mtd->_read().

Hm, I always have a hard time using types which does not clearly say
how large they are, but okay.

> 
> > +	} addr;
> > +
> > +	struct {
> > +		u8 nbytes;
> > +		u8 buswidth;
> > +	} dummy;
> > +
> > +	struct {
> > +		u8 buswidth;
> > +		enum spi_mem_data_dir dir;
> > +		unsigned int nbytes;
> > +		/* buf.{in,out} must be DMA-able. */
> > +		union {
> > +			void *in;
> > +			const void *out;
> > +		} buf;
> > +	} data;
> > +};
> > +  
> 
> Some flash devices support Dual/Quad DDR (Double Data Rate) mode and the
> SPI controller driver would need to know this information. We will need
> to add a field for that.

Well, let's wait until we actually need that.

> 
> Currently, there are drivers under mtd/spi-nor/ that need to know
> page/sector/total size of flash memory(info available in
> -`struct spi_nor). We would need a way to provide this info to spi_mem
> drivers, if we ever plan to move drivers under mtd/spi-nor to spi/

Again, we'll see when we'll try to move them, but I hope still we won't
need that. Looks like the kind of information I'd like to keep away
from spi controller drivers.
Boris Brezillon April 12, 2018, 7:59 p.m. | #3
On Thu, 12 Apr 2018 17:10:05 +0200
Boris Brezillon <boris.brezillon@bootlin.com> wrote:

> On Thu, 12 Apr 2018 20:08:28 +0530
> Vignesh R <vigneshr@ti.com> wrote:
> 
> > Hi,
> > 
> > - Sourav Poddar <sourav.poddar@ti.com> mail ID no longer valid.
> > 
> > On Wednesday 11 April 2018 04:14 AM, Boris Brezillon wrote:  
> > > Some controllers are exposing high-level interfaces to access various
> > > kind of SPI memories. Unfortunately they do not fit in the current
> > > spi_controller model and usually have drivers placed in
> > > drivers/mtd/spi-nor which are only supporting SPI NORs and not SPI
> > > memories in general.
> > > 
> > > This is an attempt at defining a SPI memory interface which works for
> > > all kinds of SPI memories (NORs, NANDs, SRAMs).
> > > 
> > > Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
> > > ---    
> > 
> > [...]
> >   
> > > +/**
> > > + * struct spi_mem_op - describes a SPI memory operation
> > > + * @cmd.buswidth: number of IO lines used to transmit the command
> > > + * @cmd.opcode: operation opcode
> > > + * @addr.nbytes: number of address bytes to send. Can be zero if the operation
> > > + *		 does not need to send an address
> > > + * @addr.buswidth: number of IO lines used to transmit the address cycles
> > > + * @addr.val: address value. This value is always sent MSB first on the bus.
> > > + *	      Note that only @addr.nbytes are taken into account in this
> > > + *	      address value, so users should make sure the value fits in the
> > > + *	      assigned number of bytes.
> > > + * @dummy.nbytes: number of dummy bytes to send after an opcode or address. Can
> > > + *		  be zero if the operation does not require dummy bytes
> > > + * @dummy.buswidth: number of IO lanes used to transmit the dummy bytes
> > > + * @data.buswidth: number of IO lanes used to send/receive the data
> > > + * @data.dir: direction of the transfer
> > > + * @data.buf.in: input buffer
> > > + * @data.buf.out: output buffer
> > > + */
> > > +struct spi_mem_op {
> > > +	struct {
> > > +		u8 buswidth;
> > > +		u8 opcode;
> > > +	} cmd;
> > > +
> > > +	struct {
> > > +		u8 nbytes;
> > > +		u8 buswidth;
> > > +		u64 val;    
> > 
> > You could consider using loff_t here and be consistent with
> > spi_nor_read/write() API as well as mtd->_read().  
> 
> Hm, I always have a hard time using types which does not clearly say
> how large they are, but okay.

BTW, loff_t is signed, which doesn't really make sense here, so I'd
like to keep an u64 unless you have a strong reason not to.

> 
> >   
> > > +	} addr;
> > > +
> > > +	struct {
> > > +		u8 nbytes;
> > > +		u8 buswidth;
> > > +	} dummy;
> > > +
> > > +	struct {
> > > +		u8 buswidth;
> > > +		enum spi_mem_data_dir dir;
> > > +		unsigned int nbytes;
> > > +		/* buf.{in,out} must be DMA-able. */
> > > +		union {
> > > +			void *in;
> > > +			const void *out;
> > > +		} buf;
> > > +	} data;
> > > +};
> > > +    
> > 
> > Some flash devices support Dual/Quad DDR (Double Data Rate) mode and the
> > SPI controller driver would need to know this information. We will need
> > to add a field for that.  
> 
> Well, let's wait until we actually need that.
> 
> > 
> > Currently, there are drivers under mtd/spi-nor/ that need to know
> > page/sector/total size of flash memory(info available in
> > -`struct spi_nor). We would need a way to provide this info to spi_mem
> > drivers, if we ever plan to move drivers under mtd/spi-nor to spi/  
> 
> Again, we'll see when we'll try to move them, but I hope still we won't
> need that. Looks like the kind of information I'd like to keep away
> from spi controller drivers.

Let me clarify this part. I already thought a bit about this problem,
and that's the very reason we have an intermediate layer with a spi_mem
struct pointing to the real spi_device object. The idea is to add new
fields to spi_mem object if/when we really have to. We'd also have to
add ->attach/detach() methods to spi_mem_ops so that SPI mem controller
can know when a new device is about to be accessed by a spi-mem
driver, can parse the information provided in spi_mem and configure the
controller accordingly.

Now, even if that's something I considered when designing the spi-mem
interface, I'd like to stay away from this sort of specialization as
long as possible. Why? Simply because dealing with memory specificities
like "is it a NOR, a NAND or an SRAM? Should I erase blocks before
writing data? What's the page size, sector size, eraseblock size? ..."
is not something that belongs in the SPI framework. IMHO, it should
stay in SPI mem drivers (the SPI NOR or SPI NAND framework are such SPI
mem drivers).

This being said, I see a real need for advanced features. One example I
have in mind is a "direct-mapping API", where a spi_mem user could ask
for a specific region of the memory to be directly mapped (if the
feature is supported by the controller of course). And that's something
I think we can make generic enough to consider adding it to the
spi_mem_ops interface. All we'll need is a way to say "I want to map
this portion of the memory in R, W or RW and when you need to
read/write use this spi_mem_op and patch the address based on the
actual memory address that is being accessed".

Maybe I'm wrong and some controllers actually need to know which type
of device they are dealing with, but in that case, I'm not so sure they
belong in the SPI framework at all, unless they provide a dummy mode in
which they can act as a regular SPI/SPI mem controller (i.e. send SPI
mem operations without trying to be smart and do things behind our
back).
Frieder Schrempf April 16, 2018, 10:33 a.m. | #4
Hi Boris,

On 11.04.2018 00:44, Boris Brezillon wrote:
> Some controllers are exposing high-level interfaces to access various
> kind of SPI memories. Unfortunately they do not fit in the current
> spi_controller model and usually have drivers placed in
> drivers/mtd/spi-nor which are only supporting SPI NORs and not SPI
> memories in general.
> 
> This is an attempt at defining a SPI memory interface which works for
> all kinds of SPI memories (NORs, NANDs, SRAMs).
> 
> Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
> ---

[...]

> +
> +/**
> + * spi_mem_supports_op() - Check if a memory device and the controller it is
> + *			   connected to support a specific memory operation
> + * @mem: the SPI memory
> + * @op: the memory operation to check
> + *
> + * Some controllers are only supporting Single or Dual IOs, others might only
> + * support specific opcodes, or it can even be that the controller and device
> + * both support Quad IOs but the hardware prevents you from using it because
> + * only 2 IO lines are connected.
> + *
> + * This function checks whether a specific operation is supported.
> + *
> + * Return: true if @op is supported, false otherwise.
> + */
> +bool spi_mem_supports_op(struct spi_mem *mem, const struct spi_mem_op *op)
> +{
> +	struct spi_controller *ctlr = mem->spi->controller;
> +
> +	if (ctlr->mem_ops->supports_op)

this misses a null check for mem_ops:
	if (ctlr->mem_ops && ctlr->mem_ops->supports_op)

> +		return ctlr->mem_ops->supports_op(mem, op);
> +
> +	return spi_mem_default_supports_op(mem, op);
> +}

[...]

Regards,

Frieder
Vignesh R April 17, 2018, 4:12 a.m. | #5
On Friday 13 April 2018 01:29 AM, Boris Brezillon wrote:
[...]
>> > > +/**
>> > > + * struct spi_mem_op - describes a SPI memory operation
>> > > + * @cmd.buswidth: number of IO lines used to transmit the command
>> > > + * @cmd.opcode: operation opcode
>> > > + * @addr.nbytes: number of address bytes to send. Can be zero if the operation
>> > > + *                does not need to send an address
>> > > + * @addr.buswidth: number of IO lines used to transmit the address cycles
>> > > + * @addr.val: address value. This value is always sent MSB first on the bus.
>> > > + *             Note that only @addr.nbytes are taken into account in this
>> > > + *             address value, so users should make sure the value fits in the
>> > > + *             assigned number of bytes.
>> > > + * @dummy.nbytes: number of dummy bytes to send after an opcode or address. Can
>> > > + *                 be zero if the operation does not require dummy bytes
>> > > + * @dummy.buswidth: number of IO lanes used to transmit the dummy bytes
>> > > + * @data.buswidth: number of IO lanes used to send/receive the data
>> > > + * @data.dir: direction of the transfer
>> > > + * @data.buf.in: input buffer
>> > > + * @data.buf.out: output buffer
>> > > + */
>> > > +struct spi_mem_op {
>> > > + struct {
>> > > +         u8 buswidth;
>> > > +         u8 opcode;
>> > > + } cmd;
>> > > +
>> > > + struct {
>> > > +         u8 nbytes;
>> > > +         u8 buswidth;
>> > > +         u64 val;    
>> > 
>> > You could consider using loff_t here and be consistent with
>> > spi_nor_read/write() API as well as mtd->_read().  
>> 
>> Hm, I always have a hard time using types which does not clearly say
>> how large they are, but okay.
> 
> BTW, loff_t is signed, which doesn't really make sense here, so I'd
> like to keep an u64 unless you have a strong reason not to.
> 

Okay.

>> 
>> >   
>> > > + } addr;
>> > > +
>> > > + struct {
>> > > +         u8 nbytes;
>> > > +         u8 buswidth;
>> > > + } dummy;
>> > > +
>> > > + struct {
>> > > +         u8 buswidth;
>> > > +         enum spi_mem_data_dir dir;
>> > > +         unsigned int nbytes;
>> > > +         /* buf.{in,out} must be DMA-able. */
>> > > +         union {
>> > > +                 void *in;
>> > > +                 const void *out;
>> > > +         } buf;
>> > > + } data;
>> > > +};
>> > > +    
>> > 
>> > Some flash devices support Dual/Quad DDR (Double Data Rate) mode and the
>> > SPI controller driver would need to know this information. We will need
>> > to add a field for that.  
>> 
>> Well, let's wait until we actually need that.
>> 
>> > 
>> > Currently, there are drivers under mtd/spi-nor/ that need to know
>> > page/sector/total size of flash memory(info available in
>> > -`struct spi_nor). We would need a way to provide this info to spi_mem
>> > drivers, if we ever plan to move drivers under mtd/spi-nor to spi/  
>> 
>> Again, we'll see when we'll try to move them, but I hope still we won't
>> need that. Looks like the kind of information I'd like to keep away
>> from spi controller drivers.
> 
> Let me clarify this part. I already thought a bit about this problem,
> and that's the very reason we have an intermediate layer with a spi_mem
> struct pointing to the real spi_device object. The idea is to add new
> fields to spi_mem object if/when we really have to. We'd also have to
> add ->attach/detach() methods to spi_mem_ops so that SPI mem controller
> can know when a new device is about to be accessed by a spi-mem
> driver, can parse the information provided in spi_mem and configure the
> controller accordingly.
> 
> Now, even if that's something I considered when designing the spi-mem
> interface, I'd like to stay away from this sort of specialization as
> long as possible. Why? Simply because dealing with memory specificities
> like "is it a NOR, a NAND or an SRAM? Should I erase blocks before
> writing data? What's the page size, sector size, eraseblock size? ..."
> is not something that belongs in the SPI framework. IMHO, it should
> stay in SPI mem drivers (the SPI NOR or SPI NAND framework are such SPI
> mem drivers).
> 
> This being said, I see a real need for advanced features. One example I
> have in mind is a "direct-mapping API", where a spi_mem user could ask
> for a specific region of the memory to be directly mapped (if the
> feature is supported by the controller of course). And that's something
> I think we can make generic enough to consider adding it to the
> spi_mem_ops interface. All we'll need is a way to say "I want to map
> this portion of the memory in R, W or RW and when you need to
> read/write use this spi_mem_op and patch the address based on the
> actual memory address that is being accessed".
>


Many of the SPI NOR controllers, especially the ones that support direct
mapping are smart and need more flash specific data. For example,
cadence-quadspi needs to know pagesize as this controller automatically
sends write enable when writes cross page boundary. I guess, such
controllers pose a problem to spi_mem_ops in passing spi_nor internal
data to drivers. Or such controllers may need to be continued to be
supported directly under spi-nor framework?

I am okay with this series in general. But, was trying to understand
which drivers will fall under spi_mem and which will continue to remain
under mtd/spi-nor


> Maybe I'm wrong and some controllers actually need to know which type
> of device they are dealing with, but in that case, I'm not so sure they
> belong in the SPI framework at all, unless they provide a dummy mode in
> which they can act as a regular SPI/SPI mem controller (i.e. send SPI
> mem operations without trying to be smart and do things behind our
> back).
>
Boris Brezillon April 18, 2018, 2:17 p.m. | #6
Hi Vignesh,

On Tue, 17 Apr 2018 09:42:18 +0530
Vignesh R <vigneshr@ti.com> wrote:

> >>   
> >> >     
> >> > > + } addr;
> >> > > +
> >> > > + struct {
> >> > > +         u8 nbytes;
> >> > > +         u8 buswidth;
> >> > > + } dummy;
> >> > > +
> >> > > + struct {
> >> > > +         u8 buswidth;
> >> > > +         enum spi_mem_data_dir dir;
> >> > > +         unsigned int nbytes;
> >> > > +         /* buf.{in,out} must be DMA-able. */
> >> > > +         union {
> >> > > +                 void *in;
> >> > > +                 const void *out;
> >> > > +         } buf;
> >> > > + } data;
> >> > > +};
> >> > > +      
> >> > 
> >> > Some flash devices support Dual/Quad DDR (Double Data Rate) mode and the
> >> > SPI controller driver would need to know this information. We will need
> >> > to add a field for that.    
> >> 
> >> Well, let's wait until we actually need that.
> >>   
> >> > 
> >> > Currently, there are drivers under mtd/spi-nor/ that need to know
> >> > page/sector/total size of flash memory(info available in
> >> > -`struct spi_nor). We would need a way to provide this info to spi_mem
> >> > drivers, if we ever plan to move drivers under mtd/spi-nor to spi/    
> >> 
> >> Again, we'll see when we'll try to move them, but I hope still we won't
> >> need that. Looks like the kind of information I'd like to keep away
> >> from spi controller drivers.  
> > 
> > Let me clarify this part. I already thought a bit about this problem,
> > and that's the very reason we have an intermediate layer with a spi_mem
> > struct pointing to the real spi_device object. The idea is to add new
> > fields to spi_mem object if/when we really have to. We'd also have to
> > add ->attach/detach() methods to spi_mem_ops so that SPI mem controller
> > can know when a new device is about to be accessed by a spi-mem
> > driver, can parse the information provided in spi_mem and configure the
> > controller accordingly.
> > 
> > Now, even if that's something I considered when designing the spi-mem
> > interface, I'd like to stay away from this sort of specialization as
> > long as possible. Why? Simply because dealing with memory specificities
> > like "is it a NOR, a NAND or an SRAM? Should I erase blocks before
> > writing data? What's the page size, sector size, eraseblock size? ..."
> > is not something that belongs in the SPI framework. IMHO, it should
> > stay in SPI mem drivers (the SPI NOR or SPI NAND framework are such SPI
> > mem drivers).
> > 
> > This being said, I see a real need for advanced features. One example I
> > have in mind is a "direct-mapping API", where a spi_mem user could ask
> > for a specific region of the memory to be directly mapped (if the
> > feature is supported by the controller of course). And that's something
> > I think we can make generic enough to consider adding it to the
> > spi_mem_ops interface. All we'll need is a way to say "I want to map
> > this portion of the memory in R, W or RW and when you need to
> > read/write use this spi_mem_op and patch the address based on the
> > actual memory address that is being accessed".
> >  
> 
> 
> Many of the SPI NOR controllers, especially the ones that support direct
> mapping are smart and need more flash specific data. For example,
> cadence-quadspi needs to know pagesize as this controller automatically
> sends write enable when writes cross page boundary. I guess, such
> controllers pose a problem to spi_mem_ops in passing spi_nor internal
> data to drivers. Or such controllers may need to be continued to be
> supported directly under spi-nor framework?

It's not decided yet. I'm not closing the door to any of those advanced
controllers yet, just need to have a closer look before taking a
decision. To me, it sounds like information that might be needed to
handle direct mapping in write mode for SPI NORs and we're not there
yet.

> 
> I am okay with this series in general. But, was trying to understand
> which drivers will fall under spi_mem and which will continue to remain
> under mtd/spi-nor

Ideally, all of them, but maybe not with all the advanced features
supported at the beginning. The only things I'd like to keep outside of
drivers/spi are controllers that are only able to send commands for a
specific type of memory (like only commands to address SPI NORs).

I'm fine discussing all of this, with real use cases to explain why we
need to expose the memory type, and the memory organization information
to SPI controller drivers, but I'd prefer to do that in a separate
thread if you don't mind.

Regards,

Boris
Boris Brezillon April 18, 2018, 2:23 p.m. | #7
Hi Frieder,

On Mon, 16 Apr 2018 12:33:54 +0200
Frieder Schrempf <frieder.schrempf@exceet.de> wrote:
 
> > +
> > +/**
> > + * spi_mem_supports_op() - Check if a memory device and the controller it is
> > + *			   connected to support a specific memory operation
> > + * @mem: the SPI memory
> > + * @op: the memory operation to check
> > + *
> > + * Some controllers are only supporting Single or Dual IOs, others might only
> > + * support specific opcodes, or it can even be that the controller and device
> > + * both support Quad IOs but the hardware prevents you from using it because
> > + * only 2 IO lines are connected.
> > + *
> > + * This function checks whether a specific operation is supported.
> > + *
> > + * Return: true if @op is supported, false otherwise.
> > + */
> > +bool spi_mem_supports_op(struct spi_mem *mem, const struct spi_mem_op *op)
> > +{
> > +	struct spi_controller *ctlr = mem->spi->controller;
> > +
> > +	if (ctlr->mem_ops->supports_op)  
> 
> this misses a null check for mem_ops:
> 	if (ctlr->mem_ops && ctlr->mem_ops->supports_op)

Yep. I'll fix that in v3.

Thanks,

Boris

Patch

diff --git a/drivers/spi/Kconfig b/drivers/spi/Kconfig
index 2d4146ce2f1b..59936ab80a0d 100644
--- a/drivers/spi/Kconfig
+++ b/drivers/spi/Kconfig
@@ -47,6 +47,13 @@  config SPI_MASTER
 
 if SPI_MASTER
 
+config SPI_MEM
+	bool "SPI memory extension"
+	help
+	  Enable this option if you want to enable the SPI memory extension.
+	  This extension is meant to simplify interaction with SPI memories
+	  by providing an high-level interface to send memory-like commands.
+
 comment "SPI Master Controller Drivers"
 
 config SPI_ALTERA
diff --git a/drivers/spi/Makefile b/drivers/spi/Makefile
index b935f10eb961..79d6f1c7b05b 100644
--- a/drivers/spi/Makefile
+++ b/drivers/spi/Makefile
@@ -8,6 +8,7 @@  ccflags-$(CONFIG_SPI_DEBUG) := -DDEBUG
 # small core, mostly translating board-specific
 # config declarations into driver model code
 obj-$(CONFIG_SPI_MASTER)		+= spi.o
+obj-$(CONFIG_SPI_MEM)			+= spi-mem.o
 obj-$(CONFIG_SPI_SPIDEV)		+= spidev.o
 obj-$(CONFIG_SPI_LOOPBACK_TEST)		+= spi-loopback-test.o
 
diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c
new file mode 100644
index 000000000000..2e6494be045c
--- /dev/null
+++ b/drivers/spi/spi-mem.c
@@ -0,0 +1,408 @@ 
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2018 Exceet Electronics GmbH
+ * Copyright (C) 2018 Bootlin
+ *
+ * Author: Boris Brezillon <boris.brezillon@bootlin.com>
+ */
+#include <linux/dmaengine.h>
+#include <linux/pm_runtime.h>
+#include <linux/spi/spi.h>
+#include <linux/spi/spi-mem.h>
+
+/**
+ * spi_controller_dma_map_mem_op_data() - DMA-map the buffer attached to a
+ *					  memory operation
+ * @ctlr: the SPI controller requesting this dma_map()
+ * @op: the memory operation containing the buffer to map
+ * @sgt: a pointer to a non-initialized sg_table that will be filled by this
+ *	 function
+ *
+ * Some controllers might want to do DMA on the data buffer embedded in @op.
+ * This helper prepares everything for you and provides a ready-to-use
+ * sg_table. This function is not intended to be called from spi drivers.
+ * Only SPI controller drivers should use it.
+ * Note that the caller must ensure the memory region pointed by
+ * op->data.buf.{in,out} is DMA-able before calling this function.
+ *
+ * Return: 0 in case of success, a negative error code otherwise.
+ */
+int spi_controller_dma_map_mem_op_data(struct spi_controller *ctlr,
+				       const struct spi_mem_op *op,
+				       struct sg_table *sgt)
+{
+	struct device *dmadev;
+
+	if (!op->data.nbytes)
+		return -EINVAL;
+
+	if (op->data.dir == SPI_MEM_DATA_OUT && ctlr->dma_tx)
+		dmadev = ctlr->dma_tx->device->dev;
+	else if (op->data.dir == SPI_MEM_DATA_IN && ctlr->dma_rx)
+		dmadev = ctlr->dma_rx->device->dev;
+	else
+		dmadev = ctlr->dev.parent;
+
+	if (!dmadev)
+		return -EINVAL;
+
+	return spi_map_buf(ctlr, dmadev, sgt, op->data.buf.in, op->data.nbytes,
+			   op->data.dir == SPI_MEM_DATA_IN ?
+			   DMA_FROM_DEVICE : DMA_TO_DEVICE);
+}
+EXPORT_SYMBOL_GPL(spi_controller_dma_map_mem_op_data);
+
+/**
+ * spi_controller_dma_unmap_mem_op_data() - DMA-unmap the buffer attached to a
+ *					    memory operation
+ * @ctlr: the SPI controller requesting this dma_unmap()
+ * @op: the memory operation containing the buffer to unmap
+ * @sgt: a pointer to an sg_table previously initialized by
+ *	 spi_controller_dma_map_mem_op_data()
+ *
+ * Some controllers might want to do DMA on the data buffer embedded in @op.
+ * This helper prepares things so that the CPU can access the
+ * op->data.buf.{in,out} buffer again.
+ *
+ * This function is not intended to be called from SPI drivers. Only SPI
+ * controller drivers should use it.
+ *
+ * This function should be called after the DMA operation has finished and is
+ * only valid if the previous spi_controller_dma_map_mem_op_data() call
+ * returned 0.
+ *
+ * Return: 0 in case of success, a negative error code otherwise.
+ */
+void spi_controller_dma_unmap_mem_op_data(struct spi_controller *ctlr,
+					  const struct spi_mem_op *op,
+					  struct sg_table *sgt)
+{
+	struct device *dmadev;
+
+	if (!op->data.nbytes)
+		return;
+
+	if (op->data.dir == SPI_MEM_DATA_OUT && ctlr->dma_tx)
+		dmadev = ctlr->dma_tx->device->dev;
+	else if (op->data.dir == SPI_MEM_DATA_IN && ctlr->dma_rx)
+		dmadev = ctlr->dma_rx->device->dev;
+	else
+		dmadev = ctlr->dev.parent;
+
+	spi_unmap_buf(ctlr, dmadev, sgt,
+		      op->data.dir == SPI_MEM_DATA_IN ?
+		      DMA_FROM_DEVICE : DMA_TO_DEVICE);
+}
+EXPORT_SYMBOL_GPL(spi_controller_dma_unmap_mem_op_data);
+
+static int spi_check_buswidth_req(struct spi_mem *mem, u8 buswidth, bool tx)
+{
+	u32 mode = mem->spi->mode;
+
+	switch (buswidth) {
+	case 1:
+		return 0;
+
+	case 2:
+		if ((tx && (mode & (SPI_TX_DUAL | SPI_TX_QUAD))) ||
+		    (!tx && (mode & (SPI_RX_DUAL | SPI_RX_QUAD))))
+			return 0;
+
+		break;
+
+	case 4:
+		if ((tx && (mode & SPI_TX_QUAD)) ||
+		    (!tx && (mode & SPI_RX_QUAD)))
+			return 0;
+
+		break;
+
+	default:
+		break;
+	}
+
+	return -ENOTSUPP;
+}
+
+static bool spi_mem_default_supports_op(struct spi_mem *mem,
+					const struct spi_mem_op *op)
+{
+	if (spi_check_buswidth_req(mem, op->cmd.buswidth, true))
+		return false;
+
+	if (op->addr.nbytes &&
+	    spi_check_buswidth_req(mem, op->addr.buswidth, true))
+		return false;
+
+	if (op->dummy.nbytes &&
+	    spi_check_buswidth_req(mem, op->dummy.buswidth, true))
+		return false;
+
+	if (op->data.nbytes &&
+	    spi_check_buswidth_req(mem, op->data.buswidth,
+				   op->data.dir == SPI_MEM_DATA_OUT))
+		return false;
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(spi_mem_default_supports_op);
+
+/**
+ * spi_mem_supports_op() - Check if a memory device and the controller it is
+ *			   connected to support a specific memory operation
+ * @mem: the SPI memory
+ * @op: the memory operation to check
+ *
+ * Some controllers are only supporting Single or Dual IOs, others might only
+ * support specific opcodes, or it can even be that the controller and device
+ * both support Quad IOs but the hardware prevents you from using it because
+ * only 2 IO lines are connected.
+ *
+ * This function checks whether a specific operation is supported.
+ *
+ * Return: true if @op is supported, false otherwise.
+ */
+bool spi_mem_supports_op(struct spi_mem *mem, const struct spi_mem_op *op)
+{
+	struct spi_controller *ctlr = mem->spi->controller;
+
+	if (ctlr->mem_ops->supports_op)
+		return ctlr->mem_ops->supports_op(mem, op);
+
+	return spi_mem_default_supports_op(mem, op);
+}
+EXPORT_SYMBOL_GPL(spi_mem_supports_op);
+
+/**
+ * spi_mem_exec_op() - Execute a memory operation
+ * @mem: the SPI memory
+ * @op: the memory operation to execute
+ *
+ * Executes a memory operation.
+ *
+ * This function first checks that @op is supported and then tries to execute
+ * it.
+ *
+ * Return: 0 in case of success, a negative error code otherwise.
+ */
+int spi_mem_exec_op(struct spi_mem *mem, const struct spi_mem_op *op)
+{
+	unsigned int tmpbufsize, xferpos = 0, totalxferlen = 0;
+	struct spi_controller *ctlr = mem->spi->controller;
+	struct spi_transfer xfers[4] = { };
+	struct spi_message msg;
+	u8 *tmpbuf;
+	int ret;
+
+	if (!spi_mem_supports_op(mem, op))
+		return -ENOTSUPP;
+
+	if (ctlr->mem_ops) {
+		/*
+		 * Flush the message queue before executing our SPI memory
+		 * operation to prevent preemption of regular SPI transfers.
+		 */
+		spi_flush_queue(ctlr);
+
+		if (ctlr->auto_runtime_pm) {
+			ret = pm_runtime_get_sync(ctlr->dev.parent);
+			if (ret < 0) {
+				dev_err(&ctlr->dev,
+					"Failed to power device: %d\n",
+					ret);
+				return ret;
+			}
+		}
+
+		mutex_lock(&ctlr->bus_lock_mutex);
+		mutex_lock(&ctlr->io_mutex);
+		ret = ctlr->mem_ops->exec_op(mem, op);
+		mutex_unlock(&ctlr->io_mutex);
+		mutex_unlock(&ctlr->bus_lock_mutex);
+
+		if (ctlr->auto_runtime_pm)
+			pm_runtime_put(ctlr->dev.parent);
+
+		/*
+		 * Some controllers only optimize specific paths (typically the
+		 * read path) and expect the core to use the regular SPI
+		 * interface in other cases.
+		 */
+		if (!ret || ret != -ENOTSUPP)
+			return ret;
+	}
+
+	tmpbufsize = sizeof(op->cmd.opcode) + op->addr.nbytes +
+		     op->dummy.nbytes;
+
+	/*
+	 * Allocate a buffer to transmit the CMD, ADDR cycles with kmalloc() so
+	 * we're guaranteed that this buffer is DMA-able, as required by the
+	 * SPI layer.
+	 */
+	tmpbuf = kzalloc(tmpbufsize, GFP_KERNEL | GFP_DMA);
+	if (!tmpbuf)
+		return -ENOMEM;
+
+	spi_message_init(&msg);
+
+	tmpbuf[0] = op->cmd.opcode;
+	xfers[xferpos].tx_buf = tmpbuf;
+	xfers[xferpos].len = sizeof(op->cmd.opcode);
+	xfers[xferpos].tx_nbits = op->cmd.buswidth;
+	spi_message_add_tail(&xfers[xferpos], &msg);
+	xferpos++;
+	totalxferlen++;
+
+	if (op->addr.nbytes) {
+		int i;
+
+		for (i = 0; i < op->addr.nbytes; i++)
+			tmpbuf[i + 1] = op->addr.val >>
+					(8 * (op->addr.nbytes - i - 1));
+
+		xfers[xferpos].tx_buf = tmpbuf + 1;
+		xfers[xferpos].len = op->addr.nbytes;
+		xfers[xferpos].tx_nbits = op->addr.buswidth;
+		spi_message_add_tail(&xfers[xferpos], &msg);
+		xferpos++;
+		totalxferlen += op->addr.nbytes;
+	}
+
+	if (op->dummy.nbytes) {
+		memset(tmpbuf + op->addr.nbytes + 1, 0xff, op->dummy.nbytes);
+		xfers[xferpos].tx_buf = tmpbuf + op->addr.nbytes + 1;
+		xfers[xferpos].len = op->dummy.nbytes;
+		xfers[xferpos].tx_nbits = op->dummy.buswidth;
+		spi_message_add_tail(&xfers[xferpos], &msg);
+		xferpos++;
+		totalxferlen += op->dummy.nbytes;
+	}
+
+	if (op->data.nbytes) {
+		if (op->data.dir == SPI_MEM_DATA_IN) {
+			xfers[xferpos].rx_buf = op->data.buf.in;
+			xfers[xferpos].rx_nbits = op->data.buswidth;
+		} else {
+			xfers[xferpos].tx_buf = op->data.buf.out;
+			xfers[xferpos].tx_nbits = op->data.buswidth;
+		}
+
+		xfers[xferpos].len = op->data.nbytes;
+		spi_message_add_tail(&xfers[xferpos], &msg);
+		xferpos++;
+		totalxferlen += op->data.nbytes;
+	}
+
+	ret = spi_sync(mem->spi, &msg);
+
+	kfree(tmpbuf);
+
+	if (ret)
+		return ret;
+
+	if (msg.actual_length != totalxferlen)
+		return -EIO;
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(spi_mem_exec_op);
+
+/**
+ * spi_mem_adjust_op_size() - Adjust the data size of a SPI mem operation to
+ *			      match controller limitations
+ * @mem: the SPI memory
+ * @op: the operation to adjust
+ *
+ * Some controllers have FIFO limitations and must split a data transfer
+ * operation into multiple ones, others require a specific alignment for
+ * optimized accesses. This function allows SPI mem drivers to split a single
+ * operation into multiple sub-operations when required.
+ *
+ * Return: a negative error code if the controller can't properly adjust @op,
+ *	   0 otherwise. Note that @op->data.nbytes will be updated if @op
+ *	   can't be handled in a single step.
+ */
+int spi_mem_adjust_op_size(struct spi_mem *mem, struct spi_mem_op *op)
+{
+	struct spi_controller *ctlr = mem->spi->controller;
+
+	if (ctlr->mem_ops && ctlr->mem_ops->adjust_op_size)
+		return ctlr->mem_ops->adjust_op_size(mem, op);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(spi_mem_adjust_op_size);
+
+static inline struct spi_mem_driver *to_spi_mem_drv(struct device_driver *drv)
+{
+	return container_of(drv, struct spi_mem_driver, spidrv.driver);
+}
+
+static int spi_mem_probe(struct spi_device *spi)
+{
+	struct spi_mem_driver *memdrv = to_spi_mem_drv(spi->dev.driver);
+	struct spi_mem *mem;
+
+	mem = devm_kzalloc(&spi->dev, sizeof(*mem), GFP_KERNEL);
+	if (!mem)
+		return -ENOMEM;
+
+	mem->spi = spi;
+	spi_set_drvdata(spi, mem);
+
+	return memdrv->probe(mem);
+}
+
+static int spi_mem_remove(struct spi_device *spi)
+{
+	struct spi_mem_driver *memdrv = to_spi_mem_drv(spi->dev.driver);
+	struct spi_mem *mem = spi_get_drvdata(spi);
+
+	if (memdrv->remove)
+		return memdrv->remove(mem);
+
+	return 0;
+}
+
+static void spi_mem_shutdown(struct spi_device *spi)
+{
+	struct spi_mem_driver *memdrv = to_spi_mem_drv(spi->dev.driver);
+	struct spi_mem *mem = spi_get_drvdata(spi);
+
+	if (memdrv->shutdown)
+		memdrv->shutdown(mem);
+}
+
+/**
+ * spi_mem_driver_register_with_owner() - Register a SPI memory driver
+ * @memdrv: the SPI memory driver to register
+ * @owner: the owner of this driver
+ *
+ * Registers a SPI memory driver.
+ *
+ * Return: 0 in case of success, a negative error core otherwise.
+ */
+
+int spi_mem_driver_register_with_owner(struct spi_mem_driver *memdrv,
+				       struct module *owner)
+{
+	memdrv->spidrv.probe = spi_mem_probe;
+	memdrv->spidrv.remove = spi_mem_remove;
+	memdrv->spidrv.shutdown = spi_mem_shutdown;
+
+	return __spi_register_driver(owner, &memdrv->spidrv);
+}
+EXPORT_SYMBOL_GPL(spi_mem_driver_register_with_owner);
+
+/**
+ * spi_mem_driver_unregister_with_owner() - Unregister a SPI memory driver
+ * @memdrv: the SPI memory driver to unregister
+ *
+ * Unregisters a SPI memory driver.
+ */
+void spi_mem_driver_unregister(struct spi_mem_driver *memdrv)
+{
+	spi_unregister_driver(&memdrv->spidrv);
+}
+EXPORT_SYMBOL_GPL(spi_mem_driver_unregister);
diff --git a/include/linux/spi/spi-mem.h b/include/linux/spi/spi-mem.h
new file mode 100644
index 000000000000..ac2e8d8f45cd
--- /dev/null
+++ b/include/linux/spi/spi-mem.h
@@ -0,0 +1,249 @@ 
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Copyright (C) 2018 Exceet Electronics GmbH
+ * Copyright (C) 2018 Bootlin
+ *
+ * Author: Boris Brezillon <boris.brezillon@bootlin.com>
+ */
+
+#ifndef __LINUX_SPI_MEM_H
+#define __LINUX_SPI_MEM_H
+
+#include <linux/spi/spi.h>
+
+#define SPI_MEM_OP_CMD(__opcode, __buswidth)			\
+	{							\
+		.buswidth = __buswidth,				\
+		.opcode = __opcode,				\
+	}
+
+#define SPI_MEM_OP_ADDR(__nbytes, __val, __buswidth)		\
+	{							\
+		.nbytes = __nbytes,				\
+		.val = __val,					\
+		.buswidth = __buswidth,				\
+	}
+
+#define SPI_MEM_OP_NO_ADDR	{ }
+
+#define SPI_MEM_OP_DUMMY(__nbytes, __buswidth)			\
+	{							\
+		.nbytes = __nbytes,				\
+		.buswidth = __buswidth,				\
+	}
+
+#define SPI_MEM_OP_NO_DUMMY	{ }
+
+#define SPI_MEM_OP_DATA_IN(__nbytes, __buf, __buswidth)		\
+	{							\
+		.dir = SPI_MEM_DATA_IN,				\
+		.nbytes = __nbytes,				\
+		.buf.in = __buf,				\
+		.buswidth = __buswidth,				\
+	}
+
+#define SPI_MEM_OP_DATA_OUT(__nbytes, __buf, __buswidth)	\
+	{							\
+		.dir = SPI_MEM_DATA_OUT,			\
+		.nbytes = __nbytes,				\
+		.buf.out = __buf,				\
+		.buswidth = __buswidth,				\
+	}
+
+#define SPI_MEM_OP_NO_DATA	{ }
+
+/**
+ * enum spi_mem_data_dir - describes the direction of a SPI memory data
+ *			   transfer from the controller perspective
+ * @SPI_MEM_DATA_IN: data coming from the SPI memory
+ * @SPI_MEM_DATA_OUT: data sent the SPI memory
+ */
+enum spi_mem_data_dir {
+	SPI_MEM_DATA_IN,
+	SPI_MEM_DATA_OUT,
+};
+
+/**
+ * struct spi_mem_op - describes a SPI memory operation
+ * @cmd.buswidth: number of IO lines used to transmit the command
+ * @cmd.opcode: operation opcode
+ * @addr.nbytes: number of address bytes to send. Can be zero if the operation
+ *		 does not need to send an address
+ * @addr.buswidth: number of IO lines used to transmit the address cycles
+ * @addr.val: address value. This value is always sent MSB first on the bus.
+ *	      Note that only @addr.nbytes are taken into account in this
+ *	      address value, so users should make sure the value fits in the
+ *	      assigned number of bytes.
+ * @dummy.nbytes: number of dummy bytes to send after an opcode or address. Can
+ *		  be zero if the operation does not require dummy bytes
+ * @dummy.buswidth: number of IO lanes used to transmit the dummy bytes
+ * @data.buswidth: number of IO lanes used to send/receive the data
+ * @data.dir: direction of the transfer
+ * @data.buf.in: input buffer
+ * @data.buf.out: output buffer
+ */
+struct spi_mem_op {
+	struct {
+		u8 buswidth;
+		u8 opcode;
+	} cmd;
+
+	struct {
+		u8 nbytes;
+		u8 buswidth;
+		u64 val;
+	} addr;
+
+	struct {
+		u8 nbytes;
+		u8 buswidth;
+	} dummy;
+
+	struct {
+		u8 buswidth;
+		enum spi_mem_data_dir dir;
+		unsigned int nbytes;
+		/* buf.{in,out} must be DMA-able. */
+		union {
+			void *in;
+			const void *out;
+		} buf;
+	} data;
+};
+
+#define SPI_MEM_OP(__cmd, __addr, __dummy, __data)		\
+	{							\
+		.cmd = __cmd,					\
+		.addr = __addr,					\
+		.dummy = __dummy,				\
+		.data = __data,					\
+	}
+
+/**
+ * struct spi_mem - describes a SPI memory device
+ * @spi: the underlying SPI device
+ * @drvpriv: spi_mem_drviver private data
+ *
+ * Extra information that describe the SPI memory device and may be needed by
+ * the controller to properly handle this device should be placed here.
+ *
+ * One example would be the device size since some controller expose their SPI
+ * mem devices through a io-mapped region.
+ */
+struct spi_mem {
+	struct spi_device *spi;
+	void *drvpriv;
+};
+
+/**
+ * struct spi_mem_set_drvdata() - attach driver private data to a SPI mem
+ *				  device
+ * @mem: memory device
+ * @data: data to attach to the memory device
+ */
+static inline void spi_mem_set_drvdata(struct spi_mem *mem, void *data)
+{
+	mem->drvpriv = data;
+}
+
+/**
+ * struct spi_mem_get_drvdata() - get driver private data attached to a SPI mem
+ *				  device
+ * @mem: memory device
+ *
+ * Return: the data attached to the mem device.
+ */
+static inline void *spi_mem_get_drvdata(struct spi_mem *mem)
+{
+	return mem->drvpriv;
+}
+
+/**
+ * struct spi_controller_mem_ops - SPI memory operations
+ * @adjust_op_size: shrink the data xfer of an operation to match controller's
+ *		    limitations (can be alignment of max RX/TX size
+ *		    limitations)
+ * @supports_op: check if an operation is supported by the controller
+ * @exec_op: execute a SPI memory operation
+ *
+ * This interface should be implemented by SPI controllers providing an
+ * high-level interface to execute SPI memory operation, which is usually the
+ * case for QSPI controllers.
+ */
+struct spi_controller_mem_ops {
+	int (*adjust_op_size)(struct spi_mem *mem, struct spi_mem_op *op);
+	bool (*supports_op)(struct spi_mem *mem,
+			    const struct spi_mem_op *op);
+	int (*exec_op)(struct spi_mem *mem,
+		       const struct spi_mem_op *op);
+};
+
+/**
+ * struct spi_mem_driver - SPI memory driver
+ * @spidrv: inherit from a SPI driver
+ * @probe: probe a SPI memory. Usually where detection/initialization takes
+ *	   place
+ * @remove: remove a SPI memory
+ * @shutdown: take appropriate action when the system is shutdown
+ *
+ * This is just a thin wrapper around a spi_driver. The core takes care of
+ * allocating the spi_mem object and forwarding the probe/remove/shutdown
+ * request to the spi_mem_driver. The reason we use this wrapper is because
+ * we might have to stuff more information into the spi_mem struct to let
+ * SPI controllers know more about the SPI memory they interact with, and
+ * having this intermediate layer allows us to do that without adding more
+ * useless fields to the spi_device object.
+ */
+struct spi_mem_driver {
+	struct spi_driver spidrv;
+	int (*probe)(struct spi_mem *mem);
+	int (*remove)(struct spi_mem *mem);
+	void (*shutdown)(struct spi_mem *mem);
+};
+
+#if IS_ENABLED(CONFIG_SPI_MEM)
+int spi_controller_dma_map_mem_op_data(struct spi_controller *ctlr,
+				       const struct spi_mem_op *op,
+				       struct sg_table *sg);
+
+void spi_controller_dma_unmap_mem_op_data(struct spi_controller *ctlr,
+					  const struct spi_mem_op *op,
+					  struct sg_table *sg);
+#else
+static inline int
+spi_controller_dma_map_mem_op_data(struct spi_controller *ctlr,
+				   const struct spi_mem_op *op,
+				   struct sg_table *sg)
+{
+	return -ENOTSUPP;
+}
+
+static inline void
+spi_controller_dma_unmap_mem_op_data(struct spi_controller *ctlr,
+				     const struct spi_mem_op *op,
+				     struct sg_table *sg)
+{
+}
+#endif /* CONFIG_SPI_MEM */
+
+int spi_mem_adjust_op_size(struct spi_mem *mem, struct spi_mem_op *op);
+
+bool spi_mem_supports_op(struct spi_mem *mem,
+			 const struct spi_mem_op *op);
+
+int spi_mem_exec_op(struct spi_mem *mem,
+		    const struct spi_mem_op *op);
+
+int spi_mem_driver_register_with_owner(struct spi_mem_driver *drv,
+				       struct module *owner);
+
+void spi_mem_driver_unregister(struct spi_mem_driver *drv);
+
+#define spi_mem_driver_register(__drv)                                  \
+	spi_mem_driver_register_with_owner(__drv, THIS_MODULE)
+
+#define module_spi_mem_driver(__drv)                                    \
+	module_driver(__drv, spi_mem_driver_register,                   \
+		      spi_mem_driver_unregister)
+
+#endif /* __LINUX_SPI_MEM_H */
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 3489fc9c0410..fb247a26fed9 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -28,6 +28,7 @@  struct property_entry;
 struct spi_controller;
 struct spi_transfer;
 struct spi_flash_read_message;
+struct spi_controller_mem_ops;
 
 /*
  * INTERFACES between SPI master-side drivers and SPI slave protocol handlers,
@@ -377,6 +378,9 @@  static inline void spi_unregister_driver(struct spi_driver *sdrv)
  *                    transfer_one callback.
  * @handle_err: the subsystem calls the driver to handle an error that occurs
  *		in the generic implementation of transfer_one_message().
+ * @mem_ops: optimized/dedicated operations for interactions with SPI memory.
+ *	     This field is optional and should only be implemented if the
+ *	     controller has native support for memory like operations.
  * @unprepare_message: undo any work done by prepare_message().
  * @slave_abort: abort the ongoing transfer request on an SPI slave controller
  * @spi_flash_read: to support spi-controller hardwares that provide
@@ -565,6 +569,9 @@  struct spi_controller {
 	void (*handle_err)(struct spi_controller *ctlr,
 			   struct spi_message *message);
 
+	/* Optimized handlers for SPI memory-like operations. */
+	const struct spi_controller_mem_ops *mem_ops;
+
 	/* gpio chip select */
 	int			*cs_gpios;