Re: [PATCH 2/2] mtd: spi-nor: add initial sysfs support

[Alexander Williams]

Hi Michael,

> On Thu, Mar 18, 2021 at 10:24 AM Michael Walle <michael@xxxxxxxx>
> wrote:
> Add support to show the name and JEDEC identifier as well as to dump the
> SFDP table. Not all flashes list their SFDP table contents in their
> datasheet. So having that is useful. It might also be helpful in bug
> reports from users.
> 
> The idea behind the sysfs module is also to have raw access to the SPI
> NOR flash device registers, which can also be useful for debugging.
> 
> Signed-off-by: Michael Walle <michael@xxxxxxxx>
> ---
>  drivers/mtd/spi-nor/Makefile |  2 +-
>  drivers/mtd/spi-nor/core.c   |  5 +++
>  drivers/mtd/spi-nor/core.h   |  3 ++
>  drivers/mtd/spi-nor/sysfs.c  | 86 ++++++++++++++++++++++++++++++++++++
>  4 files changed, 95 insertions(+), 1 deletion(-)
>  create mode 100644 drivers/mtd/spi-nor/sysfs.c
> 
> diff --git a/drivers/mtd/spi-nor/Makefile b/drivers/mtd/spi-nor/Makefile
> index 653923896205..aff308f75987 100644
> --- a/drivers/mtd/spi-nor/Makefile
> +++ b/drivers/mtd/spi-nor/Makefile
> @@ -1,6 +1,6 @@
>  # SPDX-License-Identifier: GPL-2.0
>  
> -spi-nor-objs			:= core.o sfdp.o
> +spi-nor-objs			:= core.o sfdp.o sysfs.o
>  spi-nor-objs			+= atmel.o
>  spi-nor-objs			+= catalyst.o
>  spi-nor-objs			+= eon.o
> diff --git a/drivers/mtd/spi-nor/core.c b/drivers/mtd/spi-nor/core.c
> index 4a315cb1c4db..2eaf4ba8c0f3 100644
> --- a/drivers/mtd/spi-nor/core.c
> +++ b/drivers/mtd/spi-nor/core.c
> @@ -3707,6 +3707,10 @@ static int spi_nor_probe(struct spi_mem *spimem)
>  	if (ret)
>  		return ret;
>  
> +	ret = spi_nor_sysfs_create(nor);

This appears to be racing with user space. By the time we reach probe(), the
device embedded in the spi_device has already been registered, with the uevent
sent out, right? udev may not see the new attributes created here.

Since we reuse a preexisting device throughout spi-nor, it seems awfully
challenging to be able to safely add sysfs attributes. Would it make sense to
create a spi-nor-specific device/class? Or perhaps attach these attributes to
the device in mtd_info like I've done in
https://lore.kernel.org/linux-mtd/20210428052725.530939-1-awill@xxxxxxxxxx/ ?

- Alex

> +	if (ret)
> +		return ret;
> +
>  	return mtd_device_register(&nor->mtd, data ? data->parts : NULL,
>  				   data ? data->nr_parts : 0);
>  }
> @@ -3716,6 +3720,7 @@ static int spi_nor_remove(struct spi_mem *spimem)
>  	struct spi_nor *nor = spi_mem_get_drvdata(spimem);
>  
>  	spi_nor_restore(nor);
> +	spi_nor_sysfs_remove(nor);
>  
>  	/* Clean up MTD stuff. */
>  	return mtd_device_unregister(&nor->mtd);
> diff --git a/drivers/mtd/spi-nor/core.h b/drivers/mtd/spi-nor/core.h
> index 668f22011b1d..dd592f7b62d1 100644
> --- a/drivers/mtd/spi-nor/core.h
> +++ b/drivers/mtd/spi-nor/core.h
> @@ -488,4 +488,7 @@ static struct spi_nor __maybe_unused *mtd_to_spi_nor(struct mtd_info *mtd)
>  	return mtd->priv;
>  }
>  
> +int spi_nor_sysfs_create(struct spi_nor *nor);
> +void spi_nor_sysfs_remove(struct spi_nor *nor);
> +
>  #endif /* __LINUX_MTD_SPI_NOR_INTERNAL_H */
> diff --git a/drivers/mtd/spi-nor/sysfs.c b/drivers/mtd/spi-nor/sysfs.c
> new file mode 100644
> index 000000000000..0de031e246c5
> --- /dev/null
> +++ b/drivers/mtd/spi-nor/sysfs.c
> @@ -0,0 +1,86 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/mtd/spi-nor.h>
> +#include <linux/spi/spi.h>
> +#include <linux/spi/spi-mem.h>
> +#include <linux/sysfs.h>
> +
> +#include "core.h"
> +
> +static ssize_t name_show(struct device *dev,
> +			 struct device_attribute *attr, char *buf)
> +{
> +	struct spi_device *spi = to_spi_device(dev);
> +	struct spi_mem *spimem = spi_get_drvdata(spi);
> +	struct spi_nor *nor = spi_mem_get_drvdata(spimem);
> +
> +	return sprintf(buf, "%s\n", nor->info->name);
> +}
> +static DEVICE_ATTR_RO(name);
> +
> +static ssize_t jedec_id_show(struct device *dev,
> +			     struct device_attribute *attr, char *buf)
> +{
> +	struct spi_device *spi = to_spi_device(dev);
> +	struct spi_mem *spimem = spi_get_drvdata(spi);
> +	struct spi_nor *nor = spi_mem_get_drvdata(spimem);
> +
> +	return sprintf(buf, "%*phN\n", nor->info->id_len, nor->info->id);
> +}
> +static DEVICE_ATTR_RO(jedec_id);
> +
> +static struct attribute *spi_nor_sysfs_entries[] = {
> +	&dev_attr_name.attr,
> +	&dev_attr_jedec_id.attr,
> +	NULL
> +};
> +
> +static ssize_t sfdp_read(struct file *filp, struct kobject *kobj,
> +			 struct bin_attribute *bin_attr, char *buf,
> +			 loff_t off, size_t count)
> +{
> +	struct spi_device *spi = to_spi_device(kobj_to_dev(kobj));
> +	struct spi_mem *spimem = spi_get_drvdata(spi);
> +	struct spi_nor *nor = spi_mem_get_drvdata(spimem);
> +	struct sfdp *sfdp = nor->sfdp;
> +	size_t sfdp_size = sfdp->num_dwords * sizeof(*sfdp->dwords);
> +
> +	return memory_read_from_buffer(buf, count, &off, nor->sfdp->dwords,
> +				       sfdp_size);
> +}
> +static BIN_ATTR_RO(sfdp, PAGE_SIZE);
> +
> +static struct bin_attribute *spi_nor_sysfs_bin_entries[] = {
> +	&bin_attr_sfdp,
> +	NULL
> +};
> +
> +static umode_t spi_nor_sysfs_is_bin_visible(struct kobject *kobj,
> +					    struct bin_attribute *attr, int n)
> +{
> +	struct spi_device *spi = to_spi_device(kobj_to_dev(kobj));
> +	struct spi_mem *spimem = spi_get_drvdata(spi);
> +	struct spi_nor *nor = spi_mem_get_drvdata(spimem);
> +
> +	if (attr == &bin_attr_sfdp && nor->sfdp)
> +		return 0444;
> +
> +	return 0;
> +}
> +
> +static struct attribute_group spi_nor_sysfs_attr_group = {
> +	.name		= NULL,
> +	.is_bin_visible	= spi_nor_sysfs_is_bin_visible,
> +	.attrs		= spi_nor_sysfs_entries,
> +	.bin_attrs	= spi_nor_sysfs_bin_entries,
> +};
> +
> +int spi_nor_sysfs_create(struct spi_nor *nor)
> +{
> +	return sysfs_create_group(&nor->dev->kobj, &spi_nor_sysfs_attr_group);
> +}
> +
> +void spi_nor_sysfs_remove(struct spi_nor *nor)
> +{
> +	sysfs_remove_group(&nor->dev->kobj, &spi_nor_sysfs_attr_group);
> +}
> -- 
> 2.20.1