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Re: [PATCH] natsemi long cable fix

To: netdev@xxxxxxxxxxx
Subject: Re: [PATCH] natsemi long cable fix
From: Gary Spiess <Gary.Spiess@xxxxxxxxxxxx>
Date: Tue, 15 Feb 2005 15:00:15 -0600
Cc: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx>, Jeff Garzik <jgarzik@xxxxxxxxx>
In-reply-to: <421129DE.4070101@xxxxxxxxxxxx>
References: <421129DE.4070101@xxxxxxxxxxxx>
Sender: netdev-bounce@xxxxxxxxxxx
User-agent: Mozilla Thunderbird 1.0 (Windows/20041206)
This is a minor modification to the previous patch submission that does not assume the default contents of the DSPCFG register are zero.

When used with Revision D of the DP83815, the "Recommended Registers Configuration" from page 78 of the DP83815 data sheet is not entirely compatible with the driver's "short cable patch". When the DSPCFG register is written with the value suggested in the document, then do_cable_magic() can't read the DSP coefficient and determines that all cables attached to the DP83815D are 'short', regardless of actual length. Short cables (< 30m) cause do_cable_magic to enable additional attenuation to reduce CRC and idle errors. If the extra attenuation is unintentionally enabled for long cables (> 50m?), they will not operate properly. The National Semiconductor driver, 'dp83815.c' from was used as a basis for this modification. This patch applies to the driver distributed in linux-2.6.10.

--- linux-2.6.10.orig/drivers/net/natsemi.c     2004-12-24 15:33:50.000000000 
+++ linux-2.6.10/drivers/net/natsemi.c  2005-02-14 16:45:46.000000000 -0600
@@ -441,6 +441,7 @@
#define DSPCFG_VAL      0x5040
#define SDCFG_VAL       0x008c  /* set voltage thresholds for Signal Detect */
#define DSPCFG_LOCK     0x20    /* coefficient lock bit in DSPCFG */
+#define DSPCFG_COEF    0x1000  /* see coefficient (in TSTDAT) bit in DSPCFG */
#define TSTDAT_FIXED    0xe8    /* magic number for bad coefficients */

/* misc PCI space registers */
@@ -1243,7 +1244,8 @@
                writew(1, ioaddr + PGSEL);
                writew(PMDCSR_VAL, ioaddr + PMDCSR);
                writew(TSTDAT_VAL, ioaddr + TSTDAT);
-               np->dspcfg = DSPCFG_VAL;
+               np->dspcfg = (np->srr <= SRR_DP83815_C)?
+                       DSPCFG_VAL : (DSPCFG_COEF | readw(ioaddr + DSPCFG));
                writew(np->dspcfg, ioaddr + DSPCFG);
                writew(SDCFG_VAL, ioaddr + SDCFG);
                writew(0, ioaddr + PGSEL);

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