mtd: spi-nor: hide jedec_id sysfs attribute if not present

Some non-jedec compliant flashes (like the Everspin flashes) don't have
an ID at all. Hide the attribute in this case.

Fixes: 36ac0228 ("mtd: spi-nor: add initial sysfs support")
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Takahiro Kuwano <Takahiro.Kuwano@infineon.com>
Link: https://lore.kernel.org/r/20220810220654.1297699-2-michael@walle.cc

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

@@ -5,6 +5,9 @@ Contact:	linux-mtd@lists.infradead.org
 Description:	(RO) The JEDEC ID of the SPI NOR flash as reported by the
 		flash device.
 
+		The attribute is not present if the flash doesn't support
+		the "Read JEDEC ID" command (9Fh). This is the case for
+		non-JEDEC compliant flashes.
 
 What:		/sys/bus/spi/devices/.../spi-nor/manufacturer
 Date:		April 2021

drivers/mtd/spi-nor/sysfs.c

@@ -67,6 +67,19 @@ static struct bin_attribute *spi_nor_sysfs_bin_entries[] = {
 	NULL
 };
 
+static umode_t spi_nor_sysfs_is_visible(struct kobject *kobj,
+					struct 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 == &dev_attr_jedec_id.attr && !nor->info->id_len)
+		return 0;
+
+	return 0444;
+}
+
 static umode_t spi_nor_sysfs_is_bin_visible(struct kobject *kobj,
 					    struct bin_attribute *attr, int n)
 {
@@ -82,6 +95,7 @@ static umode_t spi_nor_sysfs_is_bin_visible(struct kobject *kobj,
 
 static const struct attribute_group spi_nor_sysfs_group = {
 	.name		= "spi-nor",
+	.is_visible	= spi_nor_sysfs_is_visible,
 	.is_bin_visible	= spi_nor_sysfs_is_bin_visible,
 	.attrs		= spi_nor_sysfs_entries,
 	.bin_attrs	= spi_nor_sysfs_bin_entries,