Re: [PATCH 8/9] PCI: Ignore BAR contents when firmware left decoding disabled

From: Bjorn Helgaas
Date: Wed Mar 19 2014 - 14:54:49 EST

[+cc Ming, Rusty, Pekka, Sasha]

On Wed, Feb 26, 2014 at 12:37:57PM -0700, Bjorn Helgaas wrote:
> Don't rely on BAR contents when the command register says the BAR is
> disabled.
> If we receive a PCI device from firmware (or a hot-added device that was
> just powered up) with the MEMORY or IO enable bits in the PCI command
> register cleared, there's no reason to believe the BARs contain valid
> addresses.
> In that case, we still know the type and size of the BAR, but this
> patch marks the resource as "unset" so we have a chance to reassign it.
> Historically, we often used "BAR == 0" to decide the BAR is invalid. But 0
> is a legal BAR value, especially if the host bridge translates addresses,
> so I think it's better to decide based on the PCI command register, and
> store the conclusion in the IORESOURCE_UNSET bit.

I plan to replace this patch with the following, which only sets
IORESOURCE_UNSET when we already have been clearing the bus region start
address. (This probably should have been a separate patch to begin with,
mea culpa.)

This is intended for the v3.15 merge window, so I made the minimal change
to reduce risk.

Thanks to Ming Lei for prompting me to look at this; I think the issue he
reported with the original patch is really a problem somewhere else that
the patch just happened to expose, but the original patch was more
aggressive than necessary, so this revision tones it down a bit.


PCI: Mark 64-bit resource as IORESOURCE_UNSET if we only support 32-bit

From: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>

If we don't support 64-bit addresses, i.e., CONFIG_PHYS_ADDR_T_64BIT is not
set, we can't deal with BARs above 4GB. In this case we already pretend
the BAR contained zero; this patch also sets IORESOURCE_UNSET so we can try
to reallocate it later.

I don't think this is exactly correct: what we care about here are *bus*
addresses, not CPU addresses, so the tests of sizeof(resource_size_t)
probably should be on sizeof(dma_addr_t) instead. But this is what's been
in -next, so we'll fix that later.

Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
drivers/pci/probe.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
index 6e34498ec9f0..78335efbbb74 100644
--- a/drivers/pci/probe.c
+++ b/drivers/pci/probe.c
@@ -252,6 +252,7 @@ int __pci_read_base(struct pci_dev *dev, enum pci_bar_type type,
/* Address above 32-bit boundary; disable the BAR */
pci_write_config_dword(dev, pos, 0);
pci_write_config_dword(dev, pos + 4, 0);
+ res->flags |= IORESOURCE_UNSET;
region.start = 0;
region.end = sz64;
bar_disabled = true;
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at
Please read the FAQ at