net: phy: Expose phydev::dev_flags through sysfs

phydev::dev_flags contains a bitmask of configuration bits requested by
the consumer of a PHY device (Ethernet MAC or switch) towards the PHY
driver. Since these flags are often used for requesting LED or other
type of configuration being able to quickly audit them without
instrumenting the kernel is useful.

Signed-off-by: Florian Fainelli <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

Documentation/ABI/testing/sysfs-class-net-phydev

···
 		Boolean value indicating whether the PHY device is used in
 		standalone mode, without a net_device associated, by PHYLINK.
 		Attribute created only when this is the case.
+
+What:		/sys/class/mdio_bus/<bus>/<device>/phy_dev_flags
+Date:		March 2021
+KernelVersion:	5.13
+Contact:	[e-mail]
+Description:
+		32-bit hexadecimal number representing a bit mask of the
+		configuration bits passed from the consumer of the PHY
+		(Ethernet MAC, switch, etc.) to the PHY driver. The flags are
+		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.

drivers/net/phy/phy_device.c

···
 }
 static DEVICE_ATTR_RO(phy_has_fixups);
 
+static ssize_t phy_dev_flags_show(struct device *dev,
+				  struct device_attribute *attr,
+				  char *buf)
+{
+	struct phy_device *phydev = to_phy_device(dev);
+
+	return sprintf(buf, "0x%08x\n", phydev->dev_flags);
+}
+static DEVICE_ATTR_RO(phy_dev_flags);
+
 static struct attribute *phy_dev_attrs[] = {
 	&dev_attr_phy_id.attr,
 	&dev_attr_phy_interface.attr,
 	&dev_attr_phy_has_fixups.attr,
+	&dev_attr_phy_dev_flags.attr,
 	NULL,
 };
 ATTRIBUTE_GROUPS(phy_dev);