Re: [PATCH 1/4] pci: Update pci_set_vga_state to call arch functions

Mike Travis
2010-01-26T00:10:09Z

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.