Re: [PATCH 1/3] spi: spi-mem: add automatic poll status functions

Pratyush Yadav
2021-05-03T09:30:01Z

On 03/05/21 11:11AM, Boris Brezillon wrote:
> On Mon, 3 May 2021 14:17:44 +0530
> Pratyush Yadav <p.yadav@ti.com> wrote:
>
> > On 30/04/21 06:51PM, Boris Brezillon wrote:
> > > On Mon, 26 Apr 2021 16:39:32 +0200
> > > <patrice.chotard@foss.st.com> wrote:
> > >
> > > > From: Christophe Kerello <christophe.kerello@foss.st.com>
> > > >
> > > > With STM32 QSPI, it is possible to poll the status register of the device.
> > > > This could be done to offload the CPU during an operation (erase or
> > > > program a SPI NAND for example).
> > > >
> > > > spi_mem_poll_status API has been added to handle this feature.
> > > >
> > > > Signed-off-by: Christophe Kerello <christophe.kerello@foss.st.com>
> > > > Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
> > > > ---
> > > > drivers/spi/spi-mem.c | 34 ++++++++++++++++++++++++++++++++++
> > > > include/linux/spi/spi-mem.h | 8 ++++++++
> > > > 2 files changed, 42 insertions(+)
> > > >
> > > > diff --git a/drivers/spi/spi-mem.c b/drivers/spi/spi-mem.c
> > > > index 1513553e4080..43dce4b0efa4 100644
> > > > --- a/drivers/spi/spi-mem.c
> > > > +++ b/drivers/spi/spi-mem.c
> > > > @@ -743,6 +743,40 @@ static inline struct spi_mem_driver *to_spi_mem_drv(struct device_driver *drv)
> > > > return container_of(drv, struct spi_mem_driver, spidrv.driver);
> > > > }
> > > >
> > > > +/**
> > > > + * spi_mem_poll_status() - Poll memory device status
> > > > + * @mem: SPI memory device
> > > > + * @op: the memory operation to execute
> > > > + * @mask: status bitmask to ckeck
> > > > + * @match: status expected value
> > > > + * @timeout: timeout
> > > > + *
> > > > + * This function send a polling status request to the controller driver
> > > > + *
> > > > + * Return: 0 in case of success, -ETIMEDOUT in case of error,
> > > > + * -EOPNOTSUPP if not supported.
> > > > + */
> > > > +int spi_mem_poll_status(struct spi_mem *mem,
> > > > + const struct spi_mem_op *op,
> > > > + u8 mask, u8 match, u16 timeout)
> > > > +{
> > > > + struct spi_controller *ctlr = mem->spi->controller;
> > > > + int ret = -EOPNOTSUPP;
> > > > +
> > > > + if (ctlr->mem_ops && ctlr->mem_ops->poll_status) {
> > > > + ret = spi_mem_access_start(mem);
> > >
> > > You should probably check that op is a single byte read before
> > > accepting the command.
> >
> > Please do not discriminate against 8D-8D-8D flashes ;-).
>
> Then mask and match should probably be u16 :P. And the check as it is
> seems a bit lax to me. Drivers will of course be able to reject the op
> when there's more than one byte (or 16bit word in case of 8D) to read,
> but it feels like the core could automate that a bit.

The two 8D flashes that are currently supported in SPI NOR both have a
1-byte status register. But to read it, the read op should be 2-byte
long to avoid partial cycles at the end. The second byte is simply
discarded.

2-byte wide registers might show up in the future, but for now at least
we don't have to worry about them.

>
> >
> > >
> > > > + if (ret)
> > > > + return ret;
> > > > +
> > > > + ret = ctlr->mem_ops->poll_status(mem, op, mask, match, timeout);
> > >
> > > You also need some sort of ->poll_status_is_supported() to validate
> > > that the controller supports the status polling for this specific op (I
> >
> > I don't think a separate function is needed for checking if the poll
> > status op is supported. Return value of -EOPNOTSUPP should be able to
> > signal that. This can also be used to check if Octal DDR capable
> > controllers are able to poll using 2-byte reads.
>
> Yeah, I had something more complex in mind to avoid doing this 'try
> native mode and fall back on sw-based more if not supported' dance
> every time a status poll is requested (something similar to what we do
> for dirmaps, with a status poll desc), but I guess that's a bit
> premature (and probably uneeded).

I think Mark also suggested something similar. Make the CPU/non-CPU case
transparent to the caller. I agree with with this direction. Makes the
caller simpler.

I also mentioned in a reply to this patch that supports_op() should be
called before the op is executed. That should take care of "base"
support for the op. The poll-specific checks can go in the poll_status()
function itself. If either of those say the op is not supported, it
should fall back to CPU based polling. That's the design that makes the
most sense to me.

>
> >
> > > can imagine some controllers having a limit on the number of dummy
> > > cycles/address bytes). I guess you could just fall back on SW-based
> > > status polling if ctlr->mem_ops->poll_status() returns -ENOTSUPP.
> > >
> > > > +
> > > > + spi_mem_access_end(mem);
> > > > + }
> > > > +
> > > > + return ret;
> > > > +}
> > > > +EXPORT_SYMBOL_GPL(spi_mem_poll_status);
> > > > +
> > > > static int spi_mem_probe(struct spi_device *spi)
> > > > {
> > > > struct spi_mem_driver *memdrv = to_spi_mem_drv(spi->dev.driver);
> > > > diff --git a/include/linux/spi/spi-mem.h b/include/linux/spi/spi-mem.h
> > > > index 2b65c9edc34e..5f78917c0f68 100644
> > > > --- a/include/linux/spi/spi-mem.h
> > > > +++ b/include/linux/spi/spi-mem.h
> > > > @@ -250,6 +250,7 @@ static inline void *spi_mem_get_drvdata(struct spi_mem *mem)
> > > > * the currently mapped area), and the caller of
> > > > * spi_mem_dirmap_write() is responsible for calling it again in
> > > > * this case.
> > > > + * @poll_status: poll memory device status
> > > > *
> > > > * This interface should be implemented by SPI controllers providing an
> > > > * high-level interface to execute SPI memory operation, which is usually the
> > > > @@ -274,6 +275,9 @@ struct spi_controller_mem_ops {
> > > > u64 offs, size_t len, void *buf);
> > > > ssize_t (*dirmap_write)(struct spi_mem_dirmap_desc *desc,
> > > > u64 offs, size_t len, const void *buf);
> > > > + int (*poll_status)(struct spi_mem *mem,
> > > > + const struct spi_mem_op *op,
> > > > + u8 mask, u8 match, u16 timeout);
> > > > };
> > > >
> > > > /**
> > > > @@ -369,6 +373,10 @@ devm_spi_mem_dirmap_create(struct device *dev, struct spi_mem *mem,
> > > > void devm_spi_mem_dirmap_destroy(struct device *dev,
> > > > struct spi_mem_dirmap_desc *desc);
> > > >
> > > > +int spi_mem_poll_status(struct spi_mem *mem,
> > > > + const struct spi_mem_op *op,
> > > > + u8 mask, u8 match, u16 timeout);
> > > > +
> > > > int spi_mem_driver_register_with_owner(struct spi_mem_driver *drv,
> > > > struct module *owner);
> > > >
> >
>

--
Regards,
Pratyush Yadav
Texas Instruments Inc.