linux-kernel - Re: [PATCH] Fix boot-time hang on G31/G33 PC

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Date:	Tue, 28 Aug 2007 11:59:08 -0600
From:	Grant Grundler <grundler@...isc-linux.org>
To:	Matthew Wilcox <matthew@....cx>
Cc:	linux-pci@...ey.karlin.mff.cuni.cz, linux-kernel@...r.kernel.org,
	Robert Hancock <hancockr@...w.ca>,
	Jesse Barnes <jesse.barnes@...el.com>, Greg KH <greg@...ah.com>
Subject: Re: [PATCH] Fix boot-time hang on G31/G33 PC

On Sat, Aug 25, 2007 at 07:55:56PM -0600, Matthew Wilcox wrote:
> 
> This patch, loosely based on a patch from Robert Hancock, which was in
> turn based on a patch from Jesse Barnes, fixes a boot-time hang on my
> shiny new PC.  The 'conflict' mentioned in the patch in my case happens
> to be between mmconfig and the graphics card, but it could easily be
> between any pair of devices if they are left enabled by the BIOS and
> mappen in the wrong place.

This issue has come up before:
    http://www.uwsg.indiana.edu/hypermail/linux/kernel/0212.2/0232.html

and Ivan Kokshaysky suggested a very similar patch:
    http://www.uwsg.indiana.edu/hypermail/linux/kernel/0212.2/0324.html

cheers,
grant

> 
> Signed-off-by: Matthew Wilcox <matthew@....cx>
> 
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index 34b8dae..51ef450 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -180,11 +180,26 @@ static inline int is_64bit_memory(u32 mask)
>  	return 0;
>  }
>  
> +/*
> + * Sizing PCI BARs requires us to disable decoding, otherwise we may run
> + * into conflicts with other devices while trying to size the BAR.  Normally
> + * this isn't a problem, but it happens on some machines normally, and can
> + * happen on others during PCI device hotplug.  Don't disable BARs for host
> + * bridges, though.  Some of them do silly things like disable accesses to
> + * RAM from the CPU
> + */
>  static void pci_read_bases(struct pci_dev *dev, unsigned int howmany, int rom)
>  {
>  	unsigned int pos, reg, next;
>  	u32 l, sz;
>  	struct resource *res;
> +	u16 orig_cmd;
> +
> +	if ((dev->class >> 8) != PCI_CLASS_BRIDGE_HOST) {
> +		pci_read_config_word(dev, PCI_COMMAND, &orig_cmd);
> +		pci_write_config_word(dev, PCI_COMMAND,
> +			orig_cmd & ~(PCI_COMMAND_MEMORY | PCI_COMMAND_IO));
> +	}
>  
>  	for(pos=0; pos<howmany; pos = next) {
>  		u64 l64;
> @@ -283,6 +298,9 @@ static void pci_read_bases(struct pci_dev *dev, unsigned int howmany, int rom)
>  			}
>  		}
>  	}
> +
> +	if ((dev->class >> 8) != PCI_CLASS_BRIDGE_HOST)
> +		pci_write_config_word(dev, PCI_COMMAND, orig_cmd);
>  }
>  
>  void __devinit pci_read_bridge_bases(struct pci_bus *child)
> 
> -- 
> "Bill, look, we understand that you're interested in selling us this
> operating system, but compare it to ours.  We can't possibly take such
> a retrograde step."
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