[U-Boot] [PATCH] net: lpc32xx: Fix MDIO busy wait

[Vladimir Zapolskiy <vz@mleia.com>]

Hi Alexandre,

On 16.12.2015 20:37, amessier.tyco at gmail.com wrote:
> From: Alexandre Messier <amessier@tycoint.com>
> 
> The MDIO read function waits on the busy flag after issuing the read
> command, 

that's correct, after issuing the read command and before register read.

> while the MDIO write function waits on the busy flag before
> issuing the write command.

and that is not correct, I believe.

From the spec (MII Mgmt Indicators Register):

	For PHY Write if scan is not used:
	1. Write 0 to MCMD
	2. Write PHY address and register address to MADR
	3. Write data to MWTD
-->	4. Wait for busy bit to be cleared in MIND

	For PHY Read if scan is not used:
	1. Write 1 to MCMD
	2. Write PHY address and register address to MADR
-->	3. Wait for busy bit to be cleared in MIND
	4. Write 0 to MCMD
	5. Read data from MRDD

Could you please test/review an alternative fix? I believe it adds proper
serialization of all command sequences (read/read, read/write, write/read
and write/write). Thank you in advance.

diff --git a/drivers/net/lpc32xx_eth.c b/drivers/net/lpc32xx_eth.c
index e76e9bc..3ba5b4b 100644
--- a/drivers/net/lpc32xx_eth.c
+++ b/drivers/net/lpc32xx_eth.c
@@ -304,6 +304,13 @@ static int mii_reg_write(const char *devname, u8
phy_adr, u8 reg_ofs, u16 data)
 		return -EFAULT;
 	}

+	/* write the phy and reg addressse into the MII address reg */
+	writel((phy_adr << MADR_PHY_OFFSET) | (reg_ofs << MADR_REG_OFFSET),
+	       &regs->madr);
+
+	/* write data to the MII write register */
+	writel(data, &regs->mwtd);
+
 	/* wait till the MII is not busy */
 	timeout = MII_TIMEOUT;
 	do {
@@ -319,13 +326,6 @@ static int mii_reg_write(const char *devname, u8
phy_adr, u8 reg_ofs, u16 data)
 		return -EFAULT;
 	}

-	/* write the phy and reg addressse into the MII address reg */
-	writel((phy_adr << MADR_PHY_OFFSET) | (reg_ofs << MADR_REG_OFFSET),
-	       &regs->madr);
-
-	/* write data to the MII write register */
-	writel(data, &regs->mwtd);
-
 	/*debug("%s:(adr %d, off %d) <= %04x\n", __func__, phy_adr,
 		reg_ofs, data);*/


> This causes an issue when writing then immediately reading. As the MDIO
> module is still busy, the read command is not processed. The wait on
> busy flag in the read command passes because the previous write command
> finishes. In the end, the value returned by the read function is
> whatever was present in the MDIO data register.
> 
> Fix the issue by making sure the busy flag is cleared before issuing a
> read command. This way, it is still possible to issue a write command
> and continue executing u-boot code while the command is processed by
> the hardware. Any following MDIO read/write commands after a write
> command will wait for a cleared busy flag.

--
With best wishes,
Vladimir