netdev - [PATCH] Better MWI workaround for 21143 rev 65 chip errata

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Message-Id: <20080325113909.82BF8C2B76@solo.franken.de>
Date:	Tue, 25 Mar 2008 12:39:09 +0100 (CET)
From:	Thomas Bogendoerfer <tsbogend@...ha.franken.de>
To:	netdev@...r.kernel.org
cc:	grundler@...isc-linux.org, kyle@...isc-linux.org,
	zero@...onel-panic.org
Subject: [PATCH] Better MWI workaround for 21143 rev 65 chip errata

From: Peter Horton <zero@...onel-panic.org>

This patch works around the MWI bug on the DC21143 rev 65 Tulip by
ensuring that the receive buffers don't end on a cache line boundary
(as documented in the errata).

This patch is required for the MIPS based Cobalt Qube/RaQ as
supporting the extra PCI commands seems to reduce the chance of a hard
lockup between the Tulip and the PCI bridge.

Signed-off-by: Thomas Bogendoerfer <tsbogend@...ha.franken.de>
---

 drivers/net/tulip/tulip.h      |    7 ++++++-
 drivers/net/tulip/tulip_core.c |   19 +++++--------------
 2 files changed, 11 insertions(+), 15 deletions(-)

diff --git a/drivers/net/tulip/tulip.h b/drivers/net/tulip/tulip.h
index 3f69f53..908422f 100644
--- a/drivers/net/tulip/tulip.h
+++ b/drivers/net/tulip/tulip.h
@@ -268,7 +268,12 @@ enum t21143_csr6_bits {
 #define RX_RING_SIZE	128
 #define MEDIA_MASK     31
 
-#define PKT_BUF_SZ		1536	/* Size of each temporary Rx buffer. */
+/* The receiver on the DC21143 rev 65 can fail to close the last
+ * receive descriptor in certain circumstances (see errata) when
+ * using MWI. This can only occur if the receive buffer ends on
+ * a cache line boundary, so the "+ 4" below ensures it doesn't.
+ */
+#define PKT_BUF_SZ	(1536 + 4)	/* Size of each temporary Rx buffer. */
 
 #define TULIP_MIN_CACHE_LINE	8	/* in units of 32-bit words */
 
diff --git a/drivers/net/tulip/tulip_core.c b/drivers/net/tulip/tulip_core.c
index ed600bf..5781150 100644
--- a/drivers/net/tulip/tulip_core.c
+++ b/drivers/net/tulip/tulip_core.c
@@ -1154,18 +1154,13 @@ static void __devinit tulip_mwi_config (struct pci_dev *pdev,
 
 	tp->csr0 = csr0 = 0;
 
-	/* if we have any cache line size at all, we can do MRM */
-	csr0 |= MRM;
+	/* if we have any cache line size at all, we can do MRM and MWI */
+	csr0 |= MRM | MWI;
 
-	/* ...and barring hardware bugs, MWI */
-	if (!(tp->chip_id == DC21143 && tp->revision == 65))
-		csr0 |= MWI;
-
-	/* set or disable MWI in the standard PCI command bit.
-	 * Check for the case where  mwi is desired but not available
+	/* Enable MWI in the standard PCI command bit.
+	 * Check for the case where MWI is desired but not available
 	 */
-	if (csr0 & MWI)	pci_try_set_mwi(pdev);
-	else		pci_clear_mwi(pdev);
+	pci_try_set_mwi(pdev);
 
 	/* read result from hardware (in case bit refused to enable) */
 	pci_read_config_word(pdev, PCI_COMMAND, &pci_command);
@@ -1401,10 +1396,6 @@ static int __devinit tulip_init_one (struct pci_dev *pdev,
 #ifdef CONFIG_TULIP_MWI
 	if (!force_csr0 && (tp->flags & HAS_PCI_MWI))
 		tulip_mwi_config (pdev, dev);
-#else
-	/* MWI is broken for DC21143 rev 65... */
-	if (chip_idx == DC21143 && pdev->revision == 65)
-		tp->csr0 &= ~MWI;
 #endif
 
 	/* Stop the chip's Tx and Rx processes. */
--
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