Subject: Re: macb phy address bug?

From: Giuseppe CAVALLARO <[email-masked]>
Date: Tue, 18 Nov 2008 09:50:17 +0100

In my opinion, we need to rework this patch again for two reasons:
1) it doesn't cover the case when the PHYID is 0xffffffff.
2) we need to add an explicit comment on the PHYID check to highlight that
    this is a  work-around the broken hardware (in case we get 0xffff or 
0x0).
I've also tested it on several PHY devices: e.g. smsc lan 8700, ste101p, 
ste100p,
DP83865 National GPHY.
Where, for some of these, we need to treat the phyid=0 as wrong UID.
Please, review the attached patch.

Regards,
Peppe

David Miller wrote:
> I've applied this patch to net-2.6, thanks.
>
> As mentioned there is some rare chance that the new
> zero test could cause problems, in which case we'll
> need to undo that part.
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Fix phy_id detection also for broken hardware.

Signed-off-by: Giuseppe Cavallaro <[email-masked]>

--- phy_device.c.orig	2008-11-18 09:25:06.929041000 +0100
+++ phy_device.c	2008-11-18 09:27:15.876041000 +0100
@@ -227,7 +227,16 @@ struct phy_device * get_phy_device(struc
 	if (r)
 		return ERR_PTR(r);
 
-	/* If the phy_id is all Fs or all 0s, there is no device there */
+	/* If the phy_id is mostly Fs, there is no device there */
+	if ((phy_id & 0x1fffffff) == 0x1fffffff)
+		return NULL;
+
+	/*
+	 * Broken hardware is sometimes missing the pull down resistor on the
+	 * MDIO line, which results in reads to non-existent devices returning
+	 * 0 rather than 0xffff. Catch this here and treat 0 as a non-existent
+	 * device as well.
+	 */ 
 	if ((0xffff == phy_id) || (0x00 == phy_id))
 		return NULL;