firmware: meson_sm: Add serial number sysfs entry

The Amlogic Meson SoC Secure Monitor implements a call to retrieve an unique
SoC ID starting from the GX Family and all new families.

The serial number is simply exposed as a sysfs entry under the firmware
sysfs directory.
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>

drivers/firmware/meson/meson_sm.c

@@ -24,6 +24,7 @@
 #include <linux/printk.h>
 #include <linux/types.h>
 #include <linux/sizes.h>
+ #include <linux/slab.h>
 
 #include <linux/firmware/meson/meson_sm.h>
 
@@ -48,6 +49,7 @@ struct meson_sm_chip gxbb_chip = {
 		CMD(SM_EFUSE_READ,	0x82000030),
 		CMD(SM_EFUSE_WRITE,	0x82000031),
 		CMD(SM_EFUSE_USER_MAX,	0x82000033),
+		CMD(SM_GET_CHIP_ID,	0x82000044),
 		{ /* sentinel */ },
 	},
 };
@@ -214,6 +216,57 @@ int meson_sm_call_write(void *buffer, unsigned int size, unsigned int cmd_index,
 }
 EXPORT_SYMBOL(meson_sm_call_write);
 
+#define SM_CHIP_ID_LENGTH	119
+#define SM_CHIP_ID_OFFSET	4
+#define SM_CHIP_ID_SIZE		12
+
+static ssize_t serial_show(struct device *dev, struct device_attribute *attr,
+			 char *buf)
+{
+	uint8_t *id_buf;
+	int ret;
+
+	id_buf = kmalloc(SM_CHIP_ID_LENGTH, GFP_KERNEL);
+	if (!id_buf)
+		return -ENOMEM;
+
+	ret = meson_sm_call_read(id_buf, SM_CHIP_ID_LENGTH, SM_GET_CHIP_ID,
+				 0, 0, 0, 0, 0);
+	if (ret < 0) {
+		kfree(id_buf);
+		return ret;
+	}
+
+	ret = sprintf(buf, "%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x\n",
+			id_buf[SM_CHIP_ID_OFFSET + 0],
+			id_buf[SM_CHIP_ID_OFFSET + 1],
+			id_buf[SM_CHIP_ID_OFFSET + 2],
+			id_buf[SM_CHIP_ID_OFFSET + 3],
+			id_buf[SM_CHIP_ID_OFFSET + 4],
+			id_buf[SM_CHIP_ID_OFFSET + 5],
+			id_buf[SM_CHIP_ID_OFFSET + 6],
+			id_buf[SM_CHIP_ID_OFFSET + 7],
+			id_buf[SM_CHIP_ID_OFFSET + 8],
+			id_buf[SM_CHIP_ID_OFFSET + 9],
+			id_buf[SM_CHIP_ID_OFFSET + 10],
+			id_buf[SM_CHIP_ID_OFFSET + 11]);
+
+	kfree(id_buf);
+
+	return ret;
+}
+
+static DEVICE_ATTR_RO(serial);
+
+static struct attribute *meson_sm_sysfs_attributes[] = {
+	&dev_attr_serial.attr,
+	NULL,
+};
+
+static const struct attribute_group meson_sm_sysfs_attr_group = {
+	.attrs = meson_sm_sysfs_attributes,
+};
+
 static const struct of_device_id meson_sm_ids[] = {
 	{ .compatible = "amlogic,meson-gxbb-sm", .data = &gxbb_chip },
 	{ /* sentinel */ },
@@ -242,6 +295,9 @@ static int __init meson_sm_probe(struct platform_device *pdev)
 	fw.chip = chip;
 	pr_info("secure-monitor enabled\n");
 
+	if (sysfs_create_group(&pdev->dev.kobj, &meson_sm_sysfs_attr_group))
+		goto out_in_base;
+
 	return 0;
 
 out_in_base:

include/linux/firmware/meson/meson_sm.h

@@ -17,6 +17,7 @@ enum {
 	SM_EFUSE_READ,
 	SM_EFUSE_WRITE,
 	SM_EFUSE_USER_MAX,
+	SM_GET_CHIP_ID,
 };
 
 struct meson_sm_firmware;