r8169: fix mdio_read and update mdio_write according to hw specs

Realtek confirmed that a 20us delay is needed after mdio_read and
mdio_write operations. Reduce the delay in mdio_write, and add it
to mdio_read too. Also add a comment that the 20us is from hw specs.

Signed-off-by: Timo Teräs <timo.teras@iki.fi>
Acked-by: Francois Romieu <romieu@fr.zoreil.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 3 deletions

diff --git a/drivers/net/r8169.c b/drivers/net/r8169.c
index 03a8318d90a2..96b6cfbf0a3a 100644
--- a/drivers/net/r8169.c
+++ b/drivers/net/r8169.c
@@ -560,10 +560,10 @@ static void mdio_write(void __iomem *ioaddr, int reg_addr, int value)
                 udelay(25);
         }
         /*
-         * Some configurations require a small delay even after the write
-         * completed indication or the next write might fail.
+         * According to hardware specs a 20us delay is required after write
+         * complete indication, but before sending next command.
          */
-        udelay(25);
+        udelay(20);
 }
 
 static int mdio_read(void __iomem *ioaddr, int reg_addr)
@@ -583,6 +583,12 @@ static int mdio_read(void __iomem *ioaddr, int reg_addr)
                 }
                 udelay(25);
         }
+        /*
+         * According to hardware specs a 20us delay is required after read
+         * complete indication, but before sending next command.
+         */
+        udelay(20);
+
         return value;
 }