[PATCH V2] net: phy: Add sysfs attribute for PHY c45 identifiers.

[Jianhui Zhao <zhaojh329@gmail.com>]

If a phydevice use c45, its phy_id property is always 0, so
this adds a c45_ids sysfs attribute group contains from mmd0
to mmd31 to MDIO devices.
This attribute group can be useful when debugging problems
related to phy drivers.

Likes this:
/sys/bus/mdio_bus/devices/mdio-bus:05/c45_ids/mmd0
/sys/bus/mdio_bus/devices/mdio-bus:05/c45_ids/mmd1
...
/sys/bus/mdio_bus/devices/mdio-bus:05/c45_ids/mmd31

Signed-off-by: Jianhui Zhao <zhaojh329@gmail.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
---
V1 -> V2: putting all 32 values in a subdirectory, one file per MMD

 .../ABI/testing/sysfs-class-net-phydev        |  10 ++
 drivers/net/phy/phy_device.c                  | 103 +++++++++++++++++-
 2 files changed, 112 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-class-net-phydev b/Documentation/ABI/testing/sysfs-class-net-phydev
index ac722dd5e694..aefddd911b04 100644
--- a/Documentation/ABI/testing/sysfs-class-net-phydev
+++ b/Documentation/ABI/testing/sysfs-class-net-phydev
@@ -63,3 +63,13 @@ Description:
 		only used internally by the kernel and their placement are
 		not meant to be stable across kernel versions. This is intended
 		for facilitating the debugging of PHY drivers.
+
+What:		/sys/class/mdio_bus/<bus>/<device>/c45_ids/mmd<n>
+Date:		November 2023
+KernelVersion:	6.4
+Contact:	netdev@vger.kernel.org
+Description:
+		This attribute group c45_ids contains 32 mmd id attribute from mmd0 to mmd31
+		as reported by the device during bus enumeration, encoded in hexadecimal.
+		This ID is used to match the device with the appropriate
+		driver.
diff --git a/drivers/net/phy/phy_device.c b/drivers/net/phy/phy_device.c
index 17d0d0555a79..c09282818d45 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -602,7 +602,108 @@ static struct attribute *phy_dev_attrs[] = {
 	&dev_attr_phy_dev_flags.attr,
 	NULL,
 };
-ATTRIBUTE_GROUPS(phy_dev);
+
+static const struct attribute_group phy_dev_group = {
+	.attrs = phy_dev_attrs
+};
+
+#define DEVICE_ATTR_C45_ID(i) \
+static ssize_t \
+phy_c45_id##i##_show(struct device *dev, \
+	struct device_attribute *attr, char *buf) \
+{ \
+	struct phy_device *phydev = to_phy_device(dev); \
+\
+	if (!phydev->is_c45) \
+		return 0; \
+\
+	return sprintf(buf, "0x%.8lx\n", \
+		(unsigned long)phydev->c45_ids.device_ids[i]); \
+} \
+static struct device_attribute dev_attr_phy_c45_id##i = { \
+	.attr	= { .name = __stringify(mmd##i), .mode = 0444 }, \
+	.show	= phy_c45_id##i##_show \
+}
+
+DEVICE_ATTR_C45_ID(0);
+DEVICE_ATTR_C45_ID(1);
+DEVICE_ATTR_C45_ID(2);
+DEVICE_ATTR_C45_ID(3);
+DEVICE_ATTR_C45_ID(4);
+DEVICE_ATTR_C45_ID(5);
+DEVICE_ATTR_C45_ID(6);
+DEVICE_ATTR_C45_ID(7);
+DEVICE_ATTR_C45_ID(8);
+DEVICE_ATTR_C45_ID(9);
+DEVICE_ATTR_C45_ID(10);
+DEVICE_ATTR_C45_ID(11);
+DEVICE_ATTR_C45_ID(12);
+DEVICE_ATTR_C45_ID(13);
+DEVICE_ATTR_C45_ID(14);
+DEVICE_ATTR_C45_ID(15);
+DEVICE_ATTR_C45_ID(16);
+DEVICE_ATTR_C45_ID(17);
+DEVICE_ATTR_C45_ID(18);
+DEVICE_ATTR_C45_ID(19);
+DEVICE_ATTR_C45_ID(20);
+DEVICE_ATTR_C45_ID(21);
+DEVICE_ATTR_C45_ID(22);
+DEVICE_ATTR_C45_ID(23);
+DEVICE_ATTR_C45_ID(24);
+DEVICE_ATTR_C45_ID(25);
+DEVICE_ATTR_C45_ID(26);
+DEVICE_ATTR_C45_ID(27);
+DEVICE_ATTR_C45_ID(28);
+DEVICE_ATTR_C45_ID(29);
+DEVICE_ATTR_C45_ID(30);
+DEVICE_ATTR_C45_ID(31);
+
+static struct attribute *phy_c45_id_attrs[] = {
+	&dev_attr_phy_c45_id0.attr,
+	&dev_attr_phy_c45_id1.attr,
+	&dev_attr_phy_c45_id2.attr,
+	&dev_attr_phy_c45_id3.attr,
+	&dev_attr_phy_c45_id4.attr,
+	&dev_attr_phy_c45_id5.attr,
+	&dev_attr_phy_c45_id6.attr,
+	&dev_attr_phy_c45_id7.attr,
+	&dev_attr_phy_c45_id8.attr,
+	&dev_attr_phy_c45_id9.attr,
+	&dev_attr_phy_c45_id10.attr,
+	&dev_attr_phy_c45_id11.attr,
+	&dev_attr_phy_c45_id12.attr,
+	&dev_attr_phy_c45_id13.attr,
+	&dev_attr_phy_c45_id14.attr,
+	&dev_attr_phy_c45_id15.attr,
+	&dev_attr_phy_c45_id16.attr,
+	&dev_attr_phy_c45_id17.attr,
+	&dev_attr_phy_c45_id18.attr,
+	&dev_attr_phy_c45_id19.attr,
+	&dev_attr_phy_c45_id20.attr,
+	&dev_attr_phy_c45_id21.attr,
+	&dev_attr_phy_c45_id22.attr,
+	&dev_attr_phy_c45_id23.attr,
+	&dev_attr_phy_c45_id24.attr,
+	&dev_attr_phy_c45_id25.attr,
+	&dev_attr_phy_c45_id26.attr,
+	&dev_attr_phy_c45_id27.attr,
+	&dev_attr_phy_c45_id28.attr,
+	&dev_attr_phy_c45_id29.attr,
+	&dev_attr_phy_c45_id30.attr,
+	&dev_attr_phy_c45_id31.attr,
+	NULL,
+};
+
+static const struct attribute_group phy_dev_c45_ids_group = {
+	.name = "c45_ids",
+	.attrs = phy_c45_id_attrs
+};
+
+static const struct attribute_group *phy_dev_groups[] = {
+	&phy_dev_group,
+	&phy_dev_c45_ids_group,
+	NULL,
+};
 
 static const struct device_type mdio_bus_phy_type = {
 	.name = "PHY",
-- 
2.34.1