RE: davinci_emac/mdio: SOFT_RESET of EMAC module resets MDIO on AM1808

Hello Sudhakar,

On Fri, Feb 24, 2012 at 2:02 PM, Rajashekhara, Sudhakar [off-list ref] wrote:

On Thu, Feb 23, 2012 at 14:39:49, Christian Riesch wrote:

quoted

Hi,
I observed this behavior on a Texas Instruments AM1808 SoC (AM1808
experimenter's kit) running the current mainline kernel:

# ifconfig eth0 down
# ifconfig eth0 up
davinci_mdio davinci_mdio.0: resetting idled controller
net eth0: attached PHY driver [Generic PHY] (mii_bus:phy_addr=davinci_mdio-0:00)
# PHY: davinci_mdio-0:00 - Link is Up - 100/Full

I also observed this issue with the kernel from linux-davinci tree from
gitorious.

quoted

After each ifconfig eth0 up I get this 'resetting idled controller'
warning. I added a few debug messages to the davinci_mdio driver and
noticed that the MDIO control register was set to its reset value
(clock divider 0xff and MDIO turned off) after an ifconfig eth0 up.
Therefore, this warning is issued and a reconfiguration of the MDIO
controller is done by the driver.

Now the question was: Who is turning off the MDIO controller? After a
bit of debugging I found out that the reset of the MDIO controller
seems to be caused by these lines in the davinci_emac driver in
emac_hw_enable() in drivers/net/ethernet/ti/davinci_emac.c:

emac_write(EMAC_SOFTRESET, 1);
while (emac_read(EMAC_SOFTRESET))
        cpu_relax();

According to the AM1808 Technical Reference Manual (sections 18.2.14.1
and 18.3.3.34 in [1]), writing a 1 to the EMAC_SOFTRESET register
resets the EMAC module, but not the MDIO module. However, when I
comment out the code above, the MDIO control register is not affected
and the warning 'resetting idled controller' disappears.

But this was not the case for me. Even after commenting out the above lines,
I could still see that MDIO was getting reset.

Uh, I am sorry. I forgot to mention that there is a second
emac_write(EMAC_SOFTRESET,1); in emac_dev_stop() in davinci_emac.c. 
This one must also be commented out to make the resetting idled controller 
message go away.

The patch below shows that changes that I did. May I please ask you to try
again with these changes?

Regards, Christian

During eth0 up, the smsc_phy_config_init() function calls the mdiobus_read()
function. During this sequence if the MDIO state machine is in IDLE state,
then MDIO is reset causing the above warning message to appear.

In summary, EMAC reset is not causing the MDIO reset to happen.

---
 drivers/net/ethernet/ti/davinci_emac.c |    6 +++---
 1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/ti/davinci_emac.c b/drivers/net/ethernet/ti/davinci_emac.c
index 4b2f545..733d538 100644
--- a/drivers/net/ethernet/ti/davinci_emac.c
+++ b/drivers/net/ethernet/ti/davinci_emac.c

@@ -1290,10 +1290,10 @@ static int emac_hw_enable(struct emac_priv *priv)
 	u32 val, mbp_enable, mac_control;
 
 	/* Soft reset */
-	emac_write(EMAC_SOFTRESET, 1);
+/*	emac_write(EMAC_SOFTRESET, 1);
 	while (emac_read(EMAC_SOFTRESET))
 		cpu_relax();
-
+*/
 	/* Disable interrupt & Set pacing for more interrupts initially */
 	emac_int_disable(priv);
 

@@ -1672,7 +1672,7 @@ static int emac_dev_stop(struct net_device *ndev)
 	netif_carrier_off(ndev);
 	emac_int_disable(priv);
 	cpdma_ctlr_stop(priv->dma);
-	emac_write(EMAC_SOFTRESET, 1);
+/*	emac_write(EMAC_SOFTRESET, 1);*/
 
 	if (priv->phydev)
 		phy_disconnect(priv->phydev);

-- 
1.7.0.4