[U-Boot] DM9161BMSR must be read twice ?

[Nícolas Carneiro Lebedenco]

Hi,

I'm developing a custom board based on the AT91RM9200dk. In u-boot prompt, 
every time a enter a network command such as tftp or ping I get a message 
like this:

"MAC: error during MII initialization"

Although the command actually seems to work I was a little concerned. 
After taking a look at cpu/arm920t/at91rm9200/ether.c and 
cpu/arm920t/at91rm9200/dm9161.c I realized the problem was at
the function UCHAR dm9161_GetLinkSpeed (AT91PS_EMAC p_mac) in dm9161.c. 
Apparently, the link status bit at BMSR register is indicating link down even 
when it's not.  

I googled for it and found at http://www.davicom.com.tw/page1.aspx?no=149749 a 
FAQ for dm9000A-8 related to a similar register as follows: 

"(...) 
Q1: There are two methods for checking Link status as below: 
       1) NSR: 01H bit 6 
       2) PHY BMSR: 01 bit 2 
       Could you explain what difference is between 1) and 2)?
A1: 1) NSR: 01H bit: PHY link status now 
      2) PHY BMSR: 01 bit 2: the register will read two times. You can see 
below table for the meaning 

Read first times  Read second time  meaning
  0  0  Link fail 
  0  1  Link fail before and link ok now
  1  0  No any meaning 
  1  1  Link ok
(...)"

So I tried reading the BMSR register twice and it got the job done. Did 
anybody notice this issue ?

--- a/cpu/arm920t/at91rm9200/dm9161.c	2008-08-12 11:08:38.000000000 -0300
+++ b/cpu/arm920t/at91rm9200/dm9161.c	2008-09-02 16:26:05.000000000 -0300
@@ -70,13 +70,16 @@
  */
 UCHAR dm9161_GetLinkSpeed (AT91PS_EMAC p_mac)
 {
-	unsigned short stat1, stat2;
-
-	if (!at91rm9200_EmacReadPhy (p_mac, DM9161_BMSR, &stat1))
-		return FALSE;
+	unsigned short stat1, stat2, i;
+	
+    for (i = 2; i; --i)
+		if (!at91rm9200_EmacReadPhy (p_mac, DM9161_BMSR, &stat1))
+			return FALSE;
 
-	if (!(stat1 & DM9161_LINK_STATUS))	/* link status up? */
+	if (!(stat1 & DM9161_LINK_STATUS))	{ /* link status up? */
+		printf("Link down\n");
 		return FALSE;
+	}
 
 	if (!at91rm9200_EmacReadPhy (p_mac, DM9161_DSCSR, &stat2))
 		return FALSE;

--

Regards 

Nícolas