On Wed, 2017-07-19 at 11:28 +1000, Daniel Axtens wrote:
> Some powerpc devices provide a PCI display that isn't picked up by
> the VGA arbiter, presumably because it doesn't support the PCI
> legacy VGA ranges.
>
> Commit c2e1d84523ad ("powerpc: Set default VGA device") introduced
> an arch quirk to mark these devices as default to fix X autoconfig.
>
> The commit message stated that the patch:
>
> Ensures a default VGA is always set if a graphics adapter is present,
> even if firmware did not initialize it. If more than one graphics
> adapter is present, ensure the one initialized by firmware is set
> as the default VGA device.
>
> The patch used the following test to decide whether or not to mark
> a device as default:
>
> pci_read_config_word(pdev, PCI_COMMAND, &cmd);
> if ((cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY)) || !vga_default_device())
> vga_set_default_device(pdev);
>
> This doesn't seem like it works quite as intended. Because of the
> logical OR, the default device will be set in 2 cases:
>
> 1) if there is no default device
> OR
> 2) if this device has normal memory/IO decoding turned on
>
> This will work as intended if there is only one device, but if
> there are multiple devices, we may override the device the VGA
> arbiter picked.
>
> Instead, set a device as default if there is no default device AND
> this device decodes.
>
> This will not change behaviour on single-headed systems.
Ack.
> Cc: Brian King <brking@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Daniel Axtens <dja@xxxxxxxxxx>
>
> ---
>
> Tested in TCG (the card provided by qemu doesn't automatically
> register with vgaarb, so the relevant code path has been tested)
> but I would appreciate any tests on real hardware.
> ---
> arch/powerpc/kernel/pci-common.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
> index 341a7469cab8..c95fdda3a2dc 100644
> --- a/arch/powerpc/kernel/pci-common.c
> +++ b/arch/powerpc/kernel/pci-common.c
> @@ -1746,8 +1746,11 @@ static void fixup_vga(struct pci_dev *pdev)
> {
> u16 cmd;
>
> + if (vga_default_device())
> + return;
> +
> pci_read_config_word(pdev, PCI_COMMAND, &cmd);
> - if ((cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY)) || !vga_default_device())
> + if (cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY))
> vga_set_default_device(pdev);
>
> }
