Access to the Realtek Otto ethernet MDIO bus must wait for a free slot
between two hardware polls. The polling sequence consists of at least
17 commands on the RTL8380 devices. This delay can be nicely seen when
disabling polling completely. The following times are measured from the
last register write that sets the command bit until hardware responds
with the command finished bit set.

- average c22 read with polling enabled on all ports: ~380us
- average c22 read with polling enabled on one port: ~380us
- average c22 read with polling completely disabled: ~180us

With a default MDIO bus frequency of 2.5Mhz the bare hardware runtime
for a single command (32 bit preamble + 32 bit data) is ~25us. So the
hardware adds quite some overhead. On top of this comes the fact that
especially the RTL838x devices are low on resources (500Mhz 4Kec core
with 16K cache).

Analysis on a RTL838x device with 28 ports gives PHY access timeouts
during one of three boots while waiting for command completion. This is
currently set to 1ms. From the above explanation one can see that there
is not much headroom left.

Increase the timeout to 5ms.

Signed-off-by: Markus Stockhausen <redacted>
---
 drivers/net/mdio/mdio-realtek-rtl9300.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/mdio/mdio-realtek-rtl9300.c b/drivers/net/mdio/mdio-realtek-rtl9300.c
index e206ee3e2b1c..244af5fdeaf3 100644
--- a/drivers/net/mdio/mdio-realtek-rtl9300.c
+++ b/drivers/net/mdio/mdio-realtek-rtl9300.c

@@ -302,9 +302,9 @@ static int otto_emdio_run_cmd(struct mii_bus *bus, u32 cmd,
 	u32 cmdstate;
 	int ret;
 
-	/* Defensive pre check just in case something goes horrible wrong */
+	/* Defensive pre check just in case something goes horribly wrong */
 	ret = regmap_read_poll_timeout(priv->regmap, info->cmd_regs.c22_data,
-				       cmdstate, !(cmdstate & PHY_CTRL_CMD), 10, 1000);
+				       cmdstate, !(cmdstate & PHY_CTRL_CMD), 10, 5000);
 	if (ret)
 		return ret;
 

@@ -344,7 +344,7 @@ static int otto_emdio_run_cmd(struct mii_bus *bus, u32 cmd,
 		return ret;
 
 	ret = regmap_read_poll_timeout(priv->regmap, info->cmd_regs.c22_data,
-				       cmdstate, !(cmdstate & PHY_CTRL_CMD), 10, 1000);
+				       cmdstate, !(cmdstate & PHY_CTRL_CMD), 10, 5000);
 	if (ret)
 		return ret;
 

-- 
2.54.0