[PATCH v2, 1/1] mtd: devices: m25p80: Add PM suspend resume support

[Cyrille Pitchen]

Hi Kamal,

Le 12/09/2016 à 22:01, Kamal Dasu a écrit :
> Adding PM support so as to be able to probe spi-nor flash
> on resume. There are vendor specific commands to setup
> the transfer mode and enable read/write as part of
> spi_nor_scan(), done on initial probe and needed on resume().
> The spi-nor structure is private to the m25p driver and hence
> is the only place this can be done without having to duplicate
> code in controller driver.

Just to be sure I've understood the purpose of this patch: here we suppose
that the SPI NOR memory power supply was cut when the CPU entered its suspend
mode. So when the CPU is resumed, the SPI NOR memory power supply is enabled
again as well and the internal state of the memory is reset.

Depending on the manufacturer, we may need to send dedicated commands so the
memory is ready again (for instance, a Global Unlock Block command for SST
memories so we can perform Sector Erase and Page Program operations).
Those commands are sent from spi_nor_scan(). Hence you call spi_nor_scan()
once again from the resume callback.

If so, your patch does make sense but I wonder whether some operations done
inside spi_nor_scan() and not related to the memory itself but more to other
layers like mtd (struct mtd_info) could always be safely performed a second
time. I don't know if that issue already exists or would ever exist, if so
it might be interesting to find a mean to tell spi_nor_scan() whether it's
called for the first time on this memory (boot) or not (resume).

Best regards,

Cyrille


> Signed-off-by: Kamal Dasu <kdasu.kdev at gmail.com>
> ---
>  drivers/mtd/devices/m25p80.c | 68 +++++++++++++++++++++++++++++++-------------
>  1 file changed, 48 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
> index 9cf7fcd..48c3f64 100644
> --- a/drivers/mtd/devices/m25p80.c
> +++ b/drivers/mtd/devices/m25p80.c
> @@ -186,6 +186,39 @@ static ssize_t m25p80_read(struct spi_nor *nor, loff_t from, size_t len,
>  }
>  
>  /*
> + * scan for spi nor flash vendor parts and setup
> + * read/write mode
> + */
> +static int m25p_nor_flash_scan(struct device *dev)
> +{
> +	struct m25p *flash = dev_get_drvdata(dev);
> +	struct flash_platform_data	*data;
> +	char *flash_name = NULL;
> +	enum read_mode mode = SPI_NOR_NORMAL;
> +
> +	data = dev_get_platdata(dev);
> +
> +	/* For some (historical?) reason many platforms provide two different
> +	 * names in flash_platform_data: "name" and "type". Quite often name is
> +	 * set to "m25p80" and then "type" provides a real chip name.
> +	 * If that's the case, respect "type" and ignore a "name".
> +	 */
> +	if (data && data->type)
> +		flash_name = data->type;
> +	else if (!strcmp(flash->spi->modalias, "spi-nor"))
> +		flash_name = NULL; /* auto-detect */
> +	else
> +		flash_name = flash->spi->modalias;
> +
> +	if (flash->spi->mode & SPI_RX_QUAD)
> +		mode = SPI_NOR_QUAD;
> +	else if (flash->spi->mode & SPI_RX_DUAL)
> +		mode = SPI_NOR_DUAL;
> +
> +	return spi_nor_scan(&flash->spi_nor, flash_name, mode);
> +}
> +
> +/*
>   * board specific setup should have ensured the SPI clock used here
>   * matches what the READ command supports, at least until this driver
>   * understands FAST_READ (for clocks over 25 MHz).
> @@ -195,8 +228,6 @@ static int m25p_probe(struct spi_device *spi)
>  	struct flash_platform_data	*data;
>  	struct m25p *flash;
>  	struct spi_nor *nor;
> -	enum read_mode mode = SPI_NOR_NORMAL;
> -	char *flash_name;
>  	int ret;
>  
>  	data = dev_get_platdata(&spi->dev);
> @@ -220,27 +251,11 @@ static int m25p_probe(struct spi_device *spi)
>  	spi_set_drvdata(spi, flash);
>  	flash->spi = spi;
>  
> -	if (spi->mode & SPI_RX_QUAD)
> -		mode = SPI_NOR_QUAD;
> -	else if (spi->mode & SPI_RX_DUAL)
> -		mode = SPI_NOR_DUAL;
> -
>  	if (data && data->name)
>  		nor->mtd.name = data->name;
>  
> -	/* For some (historical?) reason many platforms provide two different
> -	 * names in flash_platform_data: "name" and "type". Quite often name is
> -	 * set to "m25p80" and then "type" provides a real chip name.
> -	 * If that's the case, respect "type" and ignore a "name".
> -	 */
> -	if (data && data->type)
> -		flash_name = data->type;
> -	else if (!strcmp(spi->modalias, "spi-nor"))
> -		flash_name = NULL; /* auto-detect */
> -	else
> -		flash_name = spi->modalias;
> +	ret = m25p_nor_flash_scan(nor->dev);
>  
> -	ret = spi_nor_scan(nor, flash_name, mode);
>  	if (ret)
>  		return ret;
>  
> @@ -248,7 +263,6 @@ static int m25p_probe(struct spi_device *spi)
>  				   data ? data->nr_parts : 0);
>  }
>  
> -
>  static int m25p_remove(struct spi_device *spi)
>  {
>  	struct m25p	*flash = spi_get_drvdata(spi);
> @@ -319,10 +333,24 @@ static const struct of_device_id m25p_of_table[] = {
>  };
>  MODULE_DEVICE_TABLE(of, m25p_of_table);
>  
> +#ifdef CONFIG_PM_SLEEP
> +static int m25p_suspend(struct device *dev)
> +{
> +	return 0;
> +}
> +
> +static int m25p_resume(struct device *dev)
> +{
> +	return m25p_nor_flash_scan(dev);
> +}
> +#endif
> +static SIMPLE_DEV_PM_OPS(m25p_pm_ops, m25p_suspend, m25p_resume);
> +
>  static struct spi_driver m25p80_driver = {
>  	.driver = {
>  		.name	= "m25p80",
>  		.of_match_table = m25p_of_table,
> +		.pm	= &m25p_pm_ops,
>  	},
>  	.id_table	= m25p_ids,
>  	.probe	= m25p_probe,
>