linux-kernel - Re: [PATCH] pci: fix nit in ROM BAR size probing

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Message-ID: <20091104090409.496540a1@jbarnes-piketon>
Date:	Wed, 4 Nov 2009 09:04:09 -0800
From:	Jesse Barnes <jbarnes@...tuousgeek.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Alex Chiang <achiang@...com>, Yu Zhao <yu.zhao@...el.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	gleb@...hat.com
Subject: Re: [PATCH] pci: fix nit in ROM BAR size probing

On Thu, 29 Oct 2009 17:24:59 +0200
"Michael S. Tsirkin" <mst@...hat.com> wrote:

> When probing for ROM BAR size, we should not
> change bits 1:10 in this BAR, because these
> bits are marked as "reserved for future use" in PCI spec,
> so changing them might have side effects.
> 
> No such issue for I/O or memory, as there is
> an implementation note in PCI spec which explicitly allows
> writing 0xfffffffff there.
> 
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>
> ---
>  drivers/pci/probe.c |    4 ++--
>  1 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 8105e32..d65aae4 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -163,12 +163,12 @@ int __pci_read_base(struct pci_dev *dev, enum
> pci_bar_type type, {
>  	u32 l, sz, mask;
>  
> -	mask = type ? ~PCI_ROM_ADDRESS_ENABLE : ~0;
> +	mask = type ? PCI_ROM_ADDRESS_MASK : ~0;
>  
>  	res->name = pci_name(dev);
>  
>  	pci_read_config_dword(dev, pos, &l);
> -	pci_write_config_dword(dev, pos, mask);
> +	pci_write_config_dword(dev, pos, l | mask);
>  	pci_read_config_dword(dev, pos, &sz);
>  	pci_write_config_dword(dev, pos, l);

Applied to linux-next, thanks.  Another possible enhancement here would
be to make the mask into a switch based on the type, since mem32 and
mem64 "BARs" (added by willy for doing BAR-like stuff) could probably
use ~0 as well.

Jesse
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