[netdrvr] tulip: Better MWI workaround for 21143 rev 65 chip errata

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@alpha.franken.de>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

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 */
 

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. */