linux-kernel - Re: [PATCH 1/4] pci: Update pci_set_vga

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Date:	Mon, 25 Jan 2010 16:09:52 -0800
From:	Mike Travis <travis@....com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Ingo Molnar <mingo@...e.hu>, Russ Anderson <rja@....com>,
	Dave Airlie <airlied@...hat.com>, Alex Chiang <achiang@...com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Robin Holt <holt@....com>, "Rafael J. Wysocki" <rjw@...k.pl>,
	Adam Jackson <ajax@...k.net>,
	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>,
	Gaetan Nadon <memsize@...eotron.ca>,
	"H. Peter Anvin" <hpa@...or.com>,
	Aaron Plattner <aplattner@...dia.com>,
	Jack Steiner <steiner@....com>,
	Tiago Vignatti <tiago.vignatti@...ia.com>,
	Cliff Wickman <cpw@....com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Christian Zander <chzander@...dia.com>,
	Yu Zhao <yu.zhao@...el.com>, linux-kernel@...r.kernel.org,
	linux-pci@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH 1/4] pci: Update pci_set_vga_state to call arch functions

Andrew Morton wrote:
> On Mon, 18 Jan 2010 12:34:13 -0600
> Mike Travis <travis@....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.
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