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

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Date:	Wed, 19 Mar 2014 12:54:23 -0600
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	linux-pci@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Ming Lei <tom.leiming@...il.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Pekka Enberg <penberg@...nel.org>,
	Sasha Levin <sasha.levin@...cle.com>
Subject: Re: [PATCH 8/9] PCI: Ignore BAR contents when firmware left decoding
 disabled

[+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.

Bjorn

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

From: Bjorn Helgaas <bhelgaas@...gle.com>

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@...gle.com>
---
 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;
--
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