PCI: Remove MRRS modification from MPS setting code

Modifying the Maximum Read Request Size to 0 (value of 128Bytes) has
massive negative ramifications on some devices.  Without knowing which
devices have this issue, do not modify from the default value when
walking the PCI-E bus in pcie_bus_safe mode.  Also, make pcie_bus_safe
the default procedure.

Tested-by: Sven Schnelle <svens@stackframe.org>
Tested-by: Simon Kirby <sim@hostway.ca>
Tested-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Reported-and-tested-by: Eric Dumazet <eric.dumazet@gmail.com>
Reported-and-tested-by: Niels Ole Salscheider <niels_ole@salscheider-online.de>
References: https://bugzilla.kernel.org/show_bug.cgi?id=42162
Signed-off-by: Jon Mason <mason@myri.com>
Acked-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/pci/pci.c

@@ -77,7 +77,7 @@ unsigned long pci_cardbus_mem_size = DEFAULT_CARDBUS_MEM_SIZE;
 unsigned long pci_hotplug_io_size  = DEFAULT_HOTPLUG_IO_SIZE;
 unsigned long pci_hotplug_mem_size = DEFAULT_HOTPLUG_MEM_SIZE;
 
-enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_PERFORMANCE;
+enum pcie_bus_config_types pcie_bus_config = PCIE_BUS_SAFE;
 
 /*
  * The default CLS is used if arch didn't set CLS explicitly and not

drivers/pci/probe.c

@@ -1396,34 +1396,37 @@ static void pcie_write_mps(struct pci_dev *dev, int mps)
 
 static void pcie_write_mrrs(struct pci_dev *dev, int mps)
 {
-	int rc, mrrs;
+	int rc, mrrs, dev_mpss;
 
-	if (pcie_bus_config == PCIE_BUS_PERFORMANCE) {
-		int dev_mpss = 128 << dev->pcie_mpss;
+	/* In the "safe" case, do not configure the MRRS.  There appear to be
+	 * issues with setting MRRS to 0 on a number of devices.
+	 */
 
-		/* For Max performance, the MRRS must be set to the largest
-		 * supported value.  However, it cannot be configured larger
-		 * than the MPS the device or the bus can support.  This assumes
-		 * that the largest MRRS available on the device cannot be
-		 * smaller than the device MPSS.
-		 */
-		mrrs = mps < dev_mpss ? mps : dev_mpss;
-	} else
-		/* In the "safe" case, configure the MRRS for fairness on the
-		 * bus by making all devices have the same size
-		 */
-		mrrs = mps;
+	if (pcie_bus_config != PCIE_BUS_PERFORMANCE)
+		return;
+
+	dev_mpss = 128 << dev->pcie_mpss;
 
+	/* For Max performance, the MRRS must be set to the largest supported
+	 * value.  However, it cannot be configured larger than the MPS the
+	 * device or the bus can support.  This assumes that the largest MRRS
+	 * available on the device cannot be smaller than the device MPSS.
+	 */
+	mrrs = min(mps, dev_mpss);
 
 	/* MRRS is a R/W register.  Invalid values can be written, but a
-	 * subsiquent read will verify if the value is acceptable or not.
+	 * subsequent read will verify if the value is acceptable or not.
 	 * If the MRRS value provided is not acceptable (e.g., too large),
 	 * shrink the value until it is acceptable to the HW.
  	 */
 	while (mrrs != pcie_get_readrq(dev) && mrrs >= 128) {
+		dev_warn(&dev->dev, "Attempting to modify the PCI-E MRRS value"
+			 " to %d.  If any issues are encountered, please try "
+			 "running with pci=pcie_bus_safe\n", mrrs);
 		rc = pcie_set_readrq(dev, mrrs);
 		if (rc)
-			dev_err(&dev->dev, "Failed attempting to set the MRRS\n");
+			dev_err(&dev->dev,
+				"Failed attempting to set the MRRS\n");
 
 		mrrs /= 2;
 	}
@@ -1436,13 +1439,13 @@ static int pcie_bus_configure_set(struct pci_dev *dev, void *data)
 	if (!pci_is_pcie(dev))
 		return 0;
 
-	dev_info(&dev->dev, "Dev MPS %d MPSS %d MRRS %d\n",
+	dev_dbg(&dev->dev, "Dev MPS %d MPSS %d MRRS %d\n",
 		 pcie_get_mps(dev), 128<<dev->pcie_mpss, pcie_get_readrq(dev));
 
 	pcie_write_mps(dev, mps);
 	pcie_write_mrrs(dev, mps);
 
-	dev_info(&dev->dev, "Dev MPS %d MPSS %d MRRS %d\n",
+	dev_dbg(&dev->dev, "Dev MPS %d MPSS %d MRRS %d\n",
 		 pcie_get_mps(dev), 128<<dev->pcie_mpss, pcie_get_readrq(dev));
 
 	return 0;