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Date:   Mon, 3 May 2021 14:59:37 +0530
From:   Pratyush Yadav <p.yadav@ti.com>
To:     Boris Brezillon <boris.brezillon@collabora.com>
CC:     <patrice.chotard@foss.st.com>, Mark Brown <broonie@kernel.org>,
        Miquel Raynal <miquel.raynal@bootlin.com>,
        Vignesh Raghavendra <vigneshr@ti.com>,
        <linux-mtd@lists.infradead.org>,
        Alexandre Torgue <alexandre.torgue@foss.st.com>,
        <linux-spi@vger.kernel.org>,
        <linux-stm32@st-md-mailman.stormreply.com>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <christophe.kerello@foss.st.com>
Subject: Re: [PATCH 1/3] spi: spi-mem: add automatic poll status functions
Message-ID: <20210503092935.vjitc7mc47wttn77@ti.com>
References: <20210426143934.25275-1-patrice.chotard@foss.st.com>
 <20210426143934.25275-2-patrice.chotard@foss.st.com>
 <20210430185104.377d1bc6@collabora.com>
 <20210503084742.7cp77snyohkdwwvv@ti.com>
 <20210503111114.26b64e25@collabora.com>
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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.