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Gmane
From: Jon Mason <mason <at> myri.com>
Subject: [PATCH] PCI: Remove MRRS modification from MPS setting code
Newsgroups: gmane.linux.kernel.pci
Date: Friday 2nd September 2011 00:25:11 UTC (over 6 years ago)
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.

Signed-off-by: Jon Mason 
---
 drivers/pci/probe.c |   36 ------------------------------------
 1 files changed, 0 insertions(+), 36 deletions(-)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 8473727..d896c5e 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -1394,41 +1394,6 @@ static void pcie_write_mps(struct pci_dev *dev, int
mps)
 		dev_err(&dev->dev, "Failed attempting to set the MPS\n");
 }
 
-static void pcie_write_mrrs(struct pci_dev *dev, int mps)
-{
-	int rc, mrrs;
-
-	if (pcie_bus_config == PCIE_BUS_PERFORMANCE) {
-		int 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 = 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;
-
-
-	/* MRRS is a R/W register.  Invalid values can be written, but a
-	 * subsiquent 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) {
-		rc = pcie_set_readrq(dev, mrrs);
-		if (rc)
-			dev_err(&dev->dev, "Failed attempting to set the MRRS\n");
-
-		mrrs /= 2;
-	}
-}
-
 static int pcie_bus_configure_set(struct pci_dev *dev, void *data)
 {
 	int mps = 128 << *(u8 *)data;
@@ -1440,7 +1405,6 @@ static int pcie_bus_configure_set(struct pci_dev
*dev, void *data)
 		 pcie_get_mps(dev), 128<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",
 		 pcie_get_mps(dev), 128<pcie_mpss, pcie_get_readrq(dev));
-- 
1.7.6
 
CD: 4ms