net: phy: introduce phy_read_mmd_poll_timeout macro

it is sometimes necessary to poll a phy register by phy_read_mmd()
function until its value satisfies some condition. introduce
phy_read_mmd_poll_timeout() macros that do this.
Suggested-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Dejin Zheng <zhengdejin5@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/linux/phy.h

@@ -24,6 +24,7 @@
 #include <linux/mod_devicetable.h>
 #include <linux/u64_stats_sync.h>
 #include <linux/irqreturn.h>
+#include <linux/iopoll.h>
 
 #include <linux/atomic.h>
 
@@ -787,6 +788,19 @@ static inline int __phy_modify_changed(struct phy_device *phydev, u32 regnum,
  */
 int phy_read_mmd(struct phy_device *phydev, int devad, u32 regnum);
 
+#define phy_read_mmd_poll_timeout(phydev, devaddr, regnum, val, cond, \
+				  sleep_us, timeout_us, sleep_before_read) \
+({ \
+	int __ret = read_poll_timeout(phy_read_mmd, val, (cond) || val < 0, \
+				  sleep_us, timeout_us, sleep_before_read, \
+				  phydev, devaddr, regnum); \
+	if (val <  0) \
+		__ret = val; \
+	if (__ret) \
+		phydev_err(phydev, "%s failed: %d\n", __func__, __ret); \
+	__ret; \
+})
+
 /**
  * __phy_read_mmd - Convenience function for reading a register
  * from an MMD on a given PHY.