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

From: Mike Travis
Date: Mon Jan 25 2010 - 19:10:18 EST

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

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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