[PATCH V3] net: phy: Add sysfs attribute for PHY c45 identifiers.

[Jianhui Zhao]

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@xxxxxxxxx>
Reviewed-by: Andrew Lunn <andrew@xxxxxxx>
Reviewed-by: Russell King <linux@xxxxxxxxxxxxxxx>
---
V2 -> V3: Use the most efficient implementation.
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                  | 115 +++++++++++++++++-
 2 files changed, 124 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@xxxxxxxxxxxxxxx
+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..b1bbbb42f020 100644
--- a/drivers/net/phy/phy_device.c
+++ b/drivers/net/phy/phy_device.c
@@ -602,7 +602,120 @@ 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
+};
+
+struct phy_c45_devid_attribute {
+	struct device_attribute attr;
+	int index;
+};
+
+#define to_phy_c45_devid_attr(ptr) \
+	container_of(ptr, struct phy_c45_devid_attribute, attr)
+
+static ssize_t phy_c45_id_show(struct device *dev,
+			       struct device_attribute *attr, char *buf)
+{
+	struct phy_c45_devid_attribute *devattr = to_phy_c45_devid_attr(attr);
+	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[devattr->index]);
+}
+
+#define DEVICE_ATTR_C45_ID(i) \
+static struct phy_c45_devid_attribute dev_attr_phy_c45_id##i = { \
+	.attr = { \
+		.attr = { .name = __stringify(mmd##i), .mode = 0444 }, \
+		.show = phy_c45_id_show \
+	}, \
+	.index = i, \
+}
+
+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.attr,
+	&dev_attr_phy_c45_id1.attr.attr,
+	&dev_attr_phy_c45_id2.attr.attr,
+	&dev_attr_phy_c45_id3.attr.attr,
+	&dev_attr_phy_c45_id4.attr.attr,
+	&dev_attr_phy_c45_id5.attr.attr,
+	&dev_attr_phy_c45_id6.attr.attr,
+	&dev_attr_phy_c45_id7.attr.attr,
+	&dev_attr_phy_c45_id8.attr.attr,
+	&dev_attr_phy_c45_id9.attr.attr,
+	&dev_attr_phy_c45_id10.attr.attr,
+	&dev_attr_phy_c45_id11.attr.attr,
+	&dev_attr_phy_c45_id12.attr.attr,
+	&dev_attr_phy_c45_id13.attr.attr,
+	&dev_attr_phy_c45_id14.attr.attr,
+	&dev_attr_phy_c45_id15.attr.attr,
+	&dev_attr_phy_c45_id16.attr.attr,
+	&dev_attr_phy_c45_id17.attr.attr,
+	&dev_attr_phy_c45_id18.attr.attr,
+	&dev_attr_phy_c45_id19.attr.attr,
+	&dev_attr_phy_c45_id20.attr.attr,
+	&dev_attr_phy_c45_id21.attr.attr,
+	&dev_attr_phy_c45_id22.attr.attr,
+	&dev_attr_phy_c45_id23.attr.attr,
+	&dev_attr_phy_c45_id24.attr.attr,
+	&dev_attr_phy_c45_id25.attr.attr,
+	&dev_attr_phy_c45_id26.attr.attr,
+	&dev_attr_phy_c45_id27.attr.attr,
+	&dev_attr_phy_c45_id28.attr.attr,
+	&dev_attr_phy_c45_id29.attr.attr,
+	&dev_attr_phy_c45_id30.attr.attr,
+	&dev_attr_phy_c45_id31.attr.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