[PATCH v3 0/3] Split default display handling out from VGA arbiter

[Daniel Axtens]

Hi Bjorn,

Yes, this works:

Tested-by: Daniel Axtens <dja at axtens.net> # arm64, ppc64-qemu-tcg


Regards,
Daniel
> On Fri, Sep 01, 2017 at 05:27:41PM +1000, Daniel Axtens wrote:
>> This patch set:
>> 
>>  - splits the default display handling out from VGA arbiter, into its
>>    own file and behind its own Kconfig option (and gives the functions
>>    better names).
>> 
>>  - adds extra detection of default devices. To be nominated, the vga
>>    arbiter and platform hooks must not have nominated a default. A
>>    card will then only be nominated if it has a driver attached and
>>    has IO or memory decoding enabled.
>> 
>>  - adds relevant documentation.
>> 
>> The practical impact of this is improved X autoconfiguration on some
>> arm64 systems.
>
> I think I gave you bad advice about trying to separate the "default
> device" idea from the VGA arbiter.
>
> It is true that the "VGA arbiter" per se is related to routing the
> legacy VGA resources, and the arbiter currently only selects a default
> device if it finds a device to which those resources are routed.
>
> We have some cases where we want to select a default device that may
> not support the legacy VGA resources, or where they might not be
> routed to the device:
>
>   - systems where we match the EFI framebuffer address with a BAR, and
>     select that device as default,
>
>   - powerpc systems where there may be no host bridge window that maps
>     to the legacy VGA resources,
>
>   - your ARM64 systems where the default device may be behind a bridge
>     that doesn't support legacy VGA routing (PCI_BRIDGE_CTL_VGA)
>
> But I think trying to split the "default device" part out from the VGA
> arbiter ends up being overkill and making things more complicated
> instead of simpler.
>
> Would something like the following work for you as well as the powerpc
> case?  On powerpc, we already use vga_set_default_device() to select a
> device that doesn't use legacy VGA resources, so maybe we can just do
> the same on ARM64?
>
> I suppose there might be wrinkles in how the arbiter deals with
> multiple graphics devices on those systems, since I don't think it
> identifies these devices that don't use the legacy resources, but it
> seems like we live with whatever those on are powerpc and probably can
> on ARM64 as well.
>
>
> diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
> index 02831a396419..0ac7aa346c69 100644
> --- a/arch/powerpc/kernel/pci-common.c
> +++ b/arch/powerpc/kernel/pci-common.c
> @@ -1740,15 +1740,3 @@ static void fixup_hide_host_resource_fsl(struct pci_dev *dev)
>  }
>  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_MOTOROLA, PCI_ANY_ID, fixup_hide_host_resource_fsl);
>  DECLARE_PCI_FIXUP_HEADER(PCI_VENDOR_ID_FREESCALE, PCI_ANY_ID, fixup_hide_host_resource_fsl);
> -
> -static void fixup_vga(struct pci_dev *pdev)
> -{
> -	u16 cmd;
> -
> -	pci_read_config_word(pdev, PCI_COMMAND, &cmd);
> -	if ((cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY)) || !vga_default_device())
> -		vga_set_default_device(pdev);
> -
> -}
> -DECLARE_PCI_FIXUP_CLASS_FINAL(PCI_ANY_ID, PCI_ANY_ID,
> -			      PCI_CLASS_DISPLAY_VGA, 8, fixup_vga);
> diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
> index 76875f6299b8..9df4802c5f04 100644
> --- a/drivers/gpu/vga/vgaarb.c
> +++ b/drivers/gpu/vga/vgaarb.c
> @@ -1468,6 +1468,21 @@ static int __init vga_arb_device_init(void)
>  			vgaarb_info(dev, "no bridge control possible\n");
>  	}
>  
> +	if (!vga_default_device()) {
> +		list_for_each_entry(vgadev, &vga_list, list) {
> +			struct device *dev = &vgadev->pdev->dev;
> +			u16 cmd;
> +
> +			pdev = vgadev->pdev;
> +			pci_read_config_word(pdev, PCI_COMMAND, &cmd);
> +			if (cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY)) {
> +				vgaarb_info(dev, "setting as boot device\n");
> +				vga_set_default_device(pdev);
> +				break;
> +			}
> +		}
> +	}
> +
>  	pr_info("loaded\n");
>  	return rc;
>  }