[PATCH v4 3/5] PCI: Do not disable memory decoding in pci_reassigndev_resource_alignment()

Yongji Xie xyjxie at linux.vnet.ibm.com
Fri Aug 12 15:42:24 AEST 2016

We should not disable memory decoding when we reassign alignment
in pci_reassigndev_resource_alignment(). It's meaningless and
have some side effects. For example, we found it would break
this kind of P2P bridge:

0001:02:02.0 PCI bridge: PLX Technology, Inc. PEX 8718 16-Lane,
5-Port PCI Express Gen 3 (8.0 GT/s) Switch (rev aa)

And it may also potentially break the PCI devices with mmio_always_on
bit set.

Besides, disabling memory decoding is not expected in some fixup
function such as fixup_vga(). The fixup_vga() read PCI_COMMAND_MEMORY
to know whether the devices has been initialized by the firmware or
not. Disabling memory decoding would cause the one initialized by
firmware may not be set as the default VGA device when more than one
graphics adapter is present.

Signed-off-by: Yongji Xie <xyjxie at linux.vnet.ibm.com>
 drivers/pci/pci.c |    8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index b8357d7..caa0894 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -5046,7 +5046,6 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev)
 	int i;
 	struct resource *r;
 	resource_size_t align, size;
-	u16 command;
 	 * VF BARs are RO zero according to SR-IOV spec Their
@@ -5069,12 +5068,7 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev)
-	dev_info(&dev->dev,
-		"Disabling memory decoding and releasing memory resources.\n");
-	pci_read_config_word(dev, PCI_COMMAND, &command);
-	command &= ~PCI_COMMAND_MEMORY;
-	pci_write_config_word(dev, PCI_COMMAND, command);
+	dev_info(&dev->dev, "Releasing memory resources.\n");
 	for (i = 0; i < PCI_BRIDGE_RESOURCES; i++) {
 		r = &dev->resource[i];
 		if (!(r->flags & IORESOURCE_MEM))

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