mtd: spi-nor: add initial sysfs support

Add support to show the manufacturer, the partname 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.
Signed-off-by: Michael Walle <michael@walle.cc>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Acked-by: Pratyush Yadav <p.yadav@ti.com>

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

+What:		/sys/bus/spi/devices/.../spi-nor/jedec_id
+Date:		April 2021
+KernelVersion:	5.14
+Contact:	linux-mtd@lists.infradead.org
+Description:	(RO) The JEDEC ID of the SPI NOR flash as reported by the
+		flash device.
+
+
+What:		/sys/bus/spi/devices/.../spi-nor/manufacturer
+Date:		April 2021
+KernelVersion:	5.14
+Contact:	linux-mtd@lists.infradead.org
+Description:	(RO) Manufacturer of the SPI NOR flash.
+
+
+What:		/sys/bus/spi/devices/.../spi-nor/partname
+Date:		April 2021
+KernelVersion:	5.14
+Contact:	linux-mtd@lists.infradead.org
+Description:	(RO) Part name of the SPI NOR flash.
+
+
+What:		/sys/bus/spi/devices/.../spi-nor/sfdp
+Date:		April 2021
+KernelVersion:	5.14
+Contact:	linux-mtd@lists.infradead.org
+Description:	(RO) This attribute is only present if the SPI NOR flash
+		device supports the "Read SFDP" command (5Ah).
+
+		If present, it contains the complete SFDP (serial flash
+		discoverable parameters) binary data of the flash.

drivers/mtd/spi-nor/Makefile

 # SPDX-License-Identifier: GPL-2.0
 
-spi-nor-objs			:= core.o sfdp.o swp.o otp.o
+spi-nor-objs			:= core.o sfdp.o swp.o otp.o sysfs.o
 spi-nor-objs			+= atmel.o
 spi-nor-objs			+= catalyst.o
 spi-nor-objs			+= eon.o

drivers/mtd/spi-nor/core.c

@@ -3459,6 +3459,7 @@ static struct spi_mem_driver spi_nor_driver = {
 		.driver = {
 			.name = "spi-nor",
 			.of_match_table = spi_nor_of_table,
+			.dev_groups = spi_nor_sysfs_groups,
 		},
 		.id_table = spi_nor_dev_ids,
 	},

drivers/mtd/spi-nor/core.h

@@ -490,6 +490,8 @@ extern const struct spi_nor_manufacturer spi_nor_winbond;
 extern const struct spi_nor_manufacturer spi_nor_xilinx;
 extern const struct spi_nor_manufacturer spi_nor_xmc;
 
+extern const struct attribute_group *spi_nor_sysfs_groups[];
+
 void spi_nor_spimem_setup_op(const struct spi_nor *nor,
 			     struct spi_mem_op *op,
 			     const enum spi_nor_protocol proto);

drivers/mtd/spi-nor/sysfs.c

+// 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 manufacturer_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 sysfs_emit(buf, "%s\n", nor->manufacturer->name);
+}
+static DEVICE_ATTR_RO(manufacturer);
+
+static ssize_t partname_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 sysfs_emit(buf, "%s\n", nor->info->name);
+}
+static DEVICE_ATTR_RO(partname);
+
+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 sysfs_emit(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_manufacturer.attr,
+	&dev_attr_partname.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, 0);
+
+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 const struct attribute_group spi_nor_sysfs_group = {
+	.name		= "spi-nor",
+	.is_bin_visible	= spi_nor_sysfs_is_bin_visible,
+	.attrs		= spi_nor_sysfs_entries,
+	.bin_attrs	= spi_nor_sysfs_bin_entries,
+};
+
+const struct attribute_group *spi_nor_sysfs_groups[] = {
+	&spi_nor_sysfs_group,
+	NULL
+};