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

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Message-ID: <20210426162610.erpt5ubeddx7paeq@ti.com>
Date:   Mon, 26 Apr 2021 21:56:12 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     <patrice.chotard@...s.st.com>
CC:     Mark Brown <broonie@...nel.org>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Boris Brezillon <boris.brezillon@...labora.com>,
        <linux-mtd@...ts.infradead.org>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>,
        <linux-spi@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <christophe.kerello@...s.st.com>
Subject: Re: [PATCH 1/3] spi: spi-mem: add automatic poll status functions

Hi,

On 26/04/21 04:39PM, patrice.chotard@...s.st.com wrote:
> From: Christophe Kerello <christophe.kerello@...s.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@...s.st.com>
> Signed-off-by: Patrice Chotard <patrice.chotard@...s.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

Technically, (status & mask) expected value. Dunno if that is obvious 
enough to not spell out explicitly.

> + * @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) {

You should call spi_mem_supports_op() before sending any ops to the 
controller. Invalid/unsupported ops can cause unexpected behavior.

> +		ret = spi_mem_access_start(mem);
> +		if (ret)
> +			return ret;
> +
> +		ret = ctlr->mem_ops->poll_status(mem, op, mask, match, timeout);

I wonder if it is better to let spi-mem core take care of the timeout 
part. On one hand it reduces code duplication on the driver side a 
little bit. Plus it makes sure drivers don't mess anything up with bad 
(or no) handling of the timeout. But on the other hand the interface 
becomes a bit awkward since you'd have to pass a struct completion 
around, and it isn't something particularly hard to get right either. 
What do you think?

> +
> +		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.