RDMA/nes: Mitigate compatibility issue regarding PCIe write credits

Under heavy load, there is an compatibility issue regarding PCIe write
credits with certain chipsets.  It can be mitigated by limiting read
requests to 256 Bytes.

This workaround is always enabled for Tbird2 on Gladius.  We also add
a module parameter to enable workaround for non-Gladius cards.

Signed-off-by: Chien Tung <chien.tin.tung@intel.com>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/nes/nes.c

@@ -95,6 +95,10 @@ unsigned int wqm_quanta = 0x10000;
 module_param(wqm_quanta, int, 0644);
 MODULE_PARM_DESC(wqm_quanta, "WQM quanta");
 
+static unsigned int limit_maxrdreqsz;
+module_param(limit_maxrdreqsz, bool, 0644);
+MODULE_PARM_DESC(limit_maxrdreqsz, "Limit max read request size to 256 Bytes");
+
 LIST_HEAD(nes_adapter_list);
 static LIST_HEAD(nes_dev_list);
 
@@ -588,6 +592,18 @@ static int __devinit nes_probe(struct pci_dev *pcidev, const struct pci_device_i
 						nesdev->nesadapter->port_count;
 	}
 
+	if ((limit_maxrdreqsz ||
+	     ((nesdev->nesadapter->phy_type[0] == NES_PHY_TYPE_GLADIUS) &&
+	      (hw_rev == NE020_REV1))) &&
+	    (pcie_get_readrq(pcidev) > 256)) {
+		if (pcie_set_readrq(pcidev, 256))
+			printk(KERN_ERR PFX "Unable to set max read request"
+				" to 256 bytes\n");
+		else
+			nes_debug(NES_DBG_INIT, "Max read request size set"
+				" to 256 bytes\n");
+	}
+
 	tasklet_init(&nesdev->dpc_tasklet, nes_dpc, (unsigned long)nesdev);
 
 	/* bring up the Control QP */

drivers/infiniband/hw/nes/nes_hw.h

@@ -40,6 +40,7 @@
 #define NES_PHY_TYPE_ARGUS     4
 #define NES_PHY_TYPE_PUMA_1G   5
 #define NES_PHY_TYPE_PUMA_10G  6
+#define NES_PHY_TYPE_GLADIUS   7
 
 #define NES_MULTICAST_PF_MAX 8