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

[Bjorn Helgaas]

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;
 }