Re: [PATCH v1] mtd: core: add sysfs nodes for querying the flash name and id

[Boris Brezillon <boris.brezillon@collabora.com>]

On Thu, 28 Mar 2019 12:59:10 +0800
Zhuohao Lee <zhuohao@chromium.org> wrote:

> Currently, we don't have sysfs nodes for querying the underlying flash
> name and flash id. This information is important especially when we
> want to know the flash detail of the defective system. In order to
> support the query, we add two pointers (*flashname, *id) into the
> mtd_info structure and create two sysfs nodes (flashname, id). This
> patch is modified based on the SPI-NOR flash system as we only have
> that system now. But the idea should be applied to the other flash
> driver like NAND flash.
> 
> The output of new sysfs nodes on my device are:
> cat /sys/devices/platform/soc/11010000.spi/spi_master/spi1/spi1.0/mtd/mtd0/flashname
> w25q64dw
> cat /sys/devices/platform/soc/11010000.spi/spi_master/spi1/spi1.0/mtd/mtd0/id
> ef6017

I'm not sure I like the idea of exposing this kind of info through
sysfs as it then makes part of the ABI. Did you consider exposing that
through debugfs?

> 
> Signed-off-by: Zhuohao Lee <zhuohao@chromium.org>
> ---
>  drivers/mtd/mtdcore.c         | 24 ++++++++++++++++++++++++
>  drivers/mtd/spi-nor/spi-nor.c |  3 +++
>  include/linux/mtd/mtd.h       |  3 +++
>  3 files changed, 30 insertions(+)
> 
> diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
> index 3ef01baef9b6..dcbe6719ad67 100644
> --- a/drivers/mtd/mtdcore.c
> +++ b/drivers/mtd/mtdcore.c
> @@ -241,6 +241,28 @@ static ssize_t mtd_name_show(struct device *dev,
>  }
>  static DEVICE_ATTR(name, S_IRUGO, mtd_name_show, NULL);
>  
> +static ssize_t mtd_flashname_show(struct device *dev,
> +		struct device_attribute *attr, char *buf)
> +{
> +	struct mtd_info *mtd = dev_get_drvdata(dev);
> +
> +	if (!mtd->flashname)
> +		return 0;
> +	return snprintf(buf, PAGE_SIZE, "%s\n", mtd->flashname);
> +}
> +static DEVICE_ATTR(flashname, S_IRUGO, mtd_flashname_show, NULL);

MTD also deals with things that are not flashes (SRAMs, ROM, ...). How
about partname?

> +
> +static ssize_t mtd_id_show(struct device *dev,
> +		struct device_attribute *attr, char *buf)
> +{
> +	struct mtd_info *mtd = dev_get_drvdata(dev);
> +
> +	if (!mtd->id)
> +		return 0;
> +	return snprintf(buf, PAGE_SIZE, "%*phN\n", mtd->id_size, mtd->id);

I'd recommend making mtd->id a string so that each flash type can
decide of the formatting, and maybe have a prefix that tells which kind
of ID this is: "spi-nor:xxxxx", "nand:xxxx", "spi-nand:xxxx".

> +}
> +static DEVICE_ATTR(id, S_IRUGO, mtd_id_show, NULL);

id is bit vague, how about partid.

> +
>  static ssize_t mtd_ecc_strength_show(struct device *dev,
>  				     struct device_attribute *attr, char *buf)
>  {
> @@ -340,6 +362,8 @@ static struct attribute *mtd_attrs[] = {
>  	&dev_attr_oobavail.attr,
>  	&dev_attr_numeraseregions.attr,
>  	&dev_attr_name.attr,
> +	&dev_attr_flashname.attr,
> +	&dev_attr_id.attr,
>  	&dev_attr_ecc_strength.attr,
>  	&dev_attr_ecc_step_size.attr,
>  	&dev_attr_corrected_bits.attr,
> diff --git a/drivers/mtd/spi-nor/spi-nor.c b/drivers/mtd/spi-nor/spi-nor.c
> index 6e13bbd1aaa5..0e10858e532c 100644
> --- a/drivers/mtd/spi-nor/spi-nor.c
> +++ b/drivers/mtd/spi-nor/spi-nor.c
> @@ -4027,6 +4027,9 @@ int spi_nor_scan(struct spi_nor *nor, const char *name,
>  
>  	if (!mtd->name)
>  		mtd->name = dev_name(dev);
> +	mtd->flashname = info->name;
> +	mtd->id = info->id;
> +	mtd->id_size = info->id_len;
>  	mtd->priv = nor;
>  	mtd->type = MTD_NORFLASH;
>  	mtd->writesize = 1;
> diff --git a/include/linux/mtd/mtd.h b/include/linux/mtd/mtd.h
> index 677768b21a1d..0a81569fa4f6 100644
> --- a/include/linux/mtd/mtd.h
> +++ b/include/linux/mtd/mtd.h
> @@ -210,6 +210,9 @@ struct mtd_info {
>  	uint32_t flags;
>  	uint32_t orig_flags; /* Flags as before running mtd checks */
>  	uint64_t size;	 // Total size of the MTD
> +	const char *flashname; /* The underlying flash name */
> +	const char *id; /* The ID of the flash */
> +	int id_size; /* Number of bytes of id array */
>  
>  	/* "Major" erase size for the device. Naïve users may take this
>  	 * to be the only erase size available, or may use the more detailed


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