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Date: Mon, 25 Jan 2010 16:09:52 -0800
From: Mike Travis <travis@sgi.com>
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To: Andrew Morton <akpm@linux-foundation.org>
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Subject: Re: [PATCH 1/4] pci: Update pci_set_vga_state to call arch functions
References: <20100118183412.560438000@alcatraz.americas.sgi.com>	<20100118183418.045021000@alcatraz.americas.sgi.com> <20100125155234.a2e397a1.akpm@linux-foundation.org>
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Andrew Morton wrote:
> 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.

You're right, I should have carried more from the intro page into the
actual patch.
> 
>>  
>> +/* 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.

Yes, it's only set (once) if it is a UV system.

> 
> Still, a neater solution might be
> 
> int arch_pci_set_vga_state(...) __weak
> {
> 	return 0;
> }
> 
> and then resolve it at linkage time?
> 
> 

Wouldn't the linked in stronger function then need to surround
the UV register updating with "if (uv_system)"?

Thanks for the comments Andrew.