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Date: Mon, 25 Jan 2010 15:52:34 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: Mike Travis <travis@sgi.com>
Cc: Jesse Barnes <jbarnes@virtuousgeek.org>, Ingo Molnar <mingo@elte.hu>,
       Russ Anderson <rja@sgi.com>, Dave Airlie <airlied@redhat.com>,
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       Cyrill Gorcunov <gorcunov@openvz.org>,
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       Robin Holt <holt@sgi.com>, "Rafael J. Wysocki" <rjw@sisk.pl>,
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       Christian Zander <chzander@nvidia.com>, Yu Zhao <yu.zhao@intel.com>,
       linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, x86@kernel.org
Subject: Re: [PATCH 1/4] pci: Update pci_set_vga_state to call arch
 functions
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On Mon, 18 Jan 2010 12:34:13 -0600
Mike Travis <travis@sgi.com> wrote:

> Update pci_set_vga_state to call arch dependent functions to enable
> Legacy VGA I/O transactions to be redirected to correct target.
> 

Changelog doesn't explain the reason for doing this, but it looks like
that becomes clearer in later patches.

>  
> +/* Some architectures require additional programming to enable VGA */
> +static arch_set_vga_state_t arch_set_vga_state;
> +
> +void pci_register_set_vga_state(arch_set_vga_state_t func)
> +{
> +	arch_set_vga_state = func;	/* NULL disables */
> +}
> +
> +static int pci_set_vga_state_arch(struct pci_dev *dev, bool decode,
> +		      unsigned int command_bits, bool change_bridge)
> +{
> +	if (arch_set_vga_state)
> +		return arch_set_vga_state(dev, decode, command_bits,
> +						change_bridge);
> +	return 0;
> +}

hm, that's not terribly elegant.  It's racy too, although it seems
unlikely that an arch will call pci_set_vga_state_arch() more than
once.

Still, a neater solution might be

int arch_pci_set_vga_state(...) __weak
{
	return 0;
}

and then resolve it at linkage time?