mtd: spi-nor: sysfs: hide the flash name if not set

The flash name is not reliable as we saw flash ID collisions.
Hide the flash name if not set.

Signed-off-by: JaimeLiao <jaimeliao@mxic.com.tw>
Reviewed-by: Michael Walle <michael@walle.cc>
[ta: update commit subject and description and the sysfs description]
Link: https://lore.kernel.org/r/20231215082138.16063-4-tudor.ambarus@linaro.org
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>

Author: jaimeliao

Documentation/ABI/testing/sysfs-bus-spi-devices-spi-nor

@@ -25,6 +25,9 @@ KernelVersion:	5.14
 Contact:	linux-mtd@lists.infradead.org
 Description:	(RO) Part name of the SPI NOR flash.
 
+		The attribute is optional. User space should not rely on
+		it to be present or even correct. Instead, user space
+		should read the jedec_id attribute.
 
 What:		/sys/bus/spi/devices/.../spi-nor/sfdp
 Date:		April 2021

drivers/mtd/spi-nor/sysfs.c

@@ -78,6 +78,8 @@ static umode_t spi_nor_sysfs_is_visible(struct kobject *kobj,
 
 	if (attr == &dev_attr_manufacturer.attr && !nor->manufacturer)
 		return 0;
+	if (attr == &dev_attr_partname.attr && !nor->info->name)
+		return 0;
 	if (attr == &dev_attr_jedec_id.attr && !nor->info->id && !nor->id)
 		return 0;