base: soc: Add serial_number attribute to soc

Add new attribute named "serial_number" as a standard interface for
user space to acquire the serial number of the device.

For ST-Ericsson SoCs this is exposed by the cryptically named "soc_id"
attribute, but this provides a human readable standardized name for this
property.
Tested-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Signed-off-by: Vaishali Thakkar <vaishali.thakkar@linaro.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Vinod Koul <vkoul@kernel.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Documentation/ABI/testing/sysfs-devices-soc

@@ -26,6 +26,13 @@ Description:
 		Read-only attribute common to all SoCs. Contains SoC family name
 		(e.g. DB8500).
 
+What:		/sys/devices/socX/serial_number
+Date:		January 2019
+contact:	Bjorn Andersson <bjorn.andersson@linaro.org>
+Description:
+		Read-only attribute supported by most SoCs. Contains the SoC's
+		serial number, if available.
+
 What:		/sys/devices/socX/soc_id
 Date:		January 2012
 contact:	Lee Jones <lee.jones@linaro.org>

drivers/base/soc.c

@@ -33,6 +33,7 @@ static struct bus_type soc_bus_type = {
 
 static DEVICE_ATTR(machine,  S_IRUGO, soc_info_get,  NULL);
 static DEVICE_ATTR(family,   S_IRUGO, soc_info_get,  NULL);
+static DEVICE_ATTR(serial_number, S_IRUGO, soc_info_get,  NULL);
 static DEVICE_ATTR(soc_id,   S_IRUGO, soc_info_get,  NULL);
 static DEVICE_ATTR(revision, S_IRUGO, soc_info_get,  NULL);
 
@@ -57,6 +58,9 @@ static umode_t soc_attribute_mode(struct kobject *kobj,
 	if ((attr == &dev_attr_revision.attr)
 	    && (soc_dev->attr->revision != NULL))
 		return attr->mode;
+	if ((attr == &dev_attr_serial_number.attr)
+	    && (soc_dev->attr->serial_number != NULL))
+		return attr->mode;
 	if ((attr == &dev_attr_soc_id.attr)
 	    && (soc_dev->attr->soc_id != NULL))
 		return attr->mode;
@@ -77,6 +81,8 @@ static ssize_t soc_info_get(struct device *dev,
 		return sprintf(buf, "%s\n", soc_dev->attr->family);
 	if (attr == &dev_attr_revision)
 		return sprintf(buf, "%s\n", soc_dev->attr->revision);
+	if (attr == &dev_attr_serial_number)
+		return sprintf(buf, "%s\n", soc_dev->attr->serial_number);
 	if (attr == &dev_attr_soc_id)
 		return sprintf(buf, "%s\n", soc_dev->attr->soc_id);
 
@@ -87,6 +93,7 @@ static ssize_t soc_info_get(struct device *dev,
 static struct attribute *soc_attr[] = {
 	&dev_attr_machine.attr,
 	&dev_attr_family.attr,
+	&dev_attr_serial_number.attr,
 	&dev_attr_soc_id.attr,
 	&dev_attr_revision.attr,
 	NULL,

include/linux/sys_soc.h

@@ -12,6 +12,7 @@ struct soc_device_attribute {
 	const char *machine;
 	const char *family;
 	const char *revision;
+	const char *serial_number;
 	const char *soc_id;
 	const void *data;
 };