Commit e96902eb authored by Huacai Chen's avatar Huacai Chen Committed by Bjorn Helgaas
Browse files

PCI/VGA: Move non-legacy VGA detection to ADD_DEVICE path 

a37c0f48 ("vgaarb: Select a default VGA device even if there's no
legacy VGA") extended the vga_arb_device_init() subsys_initcall so it could
select a non-legacy VGA device as the default.

That failed to consider that PCI devices may be enumerated after
vga_arb_device_init(), e.g., hot-added devices or non-ACPI systems that do
PCI enumeration in pcibios_init().  Devices found then could never be
selected as the default.

One system where this is a problem is the MIPS-based Loongson where an
ASpeed AST2500 VGA device is behind a bridge that doesn't implement the VGA
Enable bit, so legacy resources are not routed to the VGA device. [1]

Fix this by moving the non-legacy VGA device selection from
vga_arb_select_default_device() to vga_arbiter_add_pci_device(), which is
called after every PCI device is enumerated, either by the
vga_arb_device_init() subsys_initcall or as an ADD_DEVICE notifier.

[1] https://lore.kernel.org/r/20210514080025.1828197-6-chenhuacai@loongson.cn

[bhelgaas: commit log, restructure]
Link: https://lore.kernel.org/r/20211015061512.2941859-5-chenhuacai@loongson.cn
Link: https://lore.kernel.org/r/20211015061512.2941859-7-chenhuacai@loongson.cn
Link: https://lore.kernel.org/r/20220224224753.297579-7-helgaas@kernel.org


Signed-off-by: default avatarHuacai Chen <chenhuacai@loongson.cn>
Signed-off-by: default avatarBjorn Helgaas <bhelgaas@google.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Zhou Wang <wangzhou1@hisilicon.com>
parent f8d81df2

drivers/pci/vgaarb.c

+32 −22
Original line number Diff line number Diff line
@@ -624,6 +624,7 @@ static bool vga_is_boot_device(struct vga_device *vgadev) 
{

	struct vga_device *boot_vga = vgadev_find(vga_default_device());

	struct pci_dev *pdev = vgadev->pdev;

	u16 cmd, boot_cmd;



	/*

	 * We select the default VGA device in this order:
@@ -661,6 +662,37 @@ static bool vga_is_boot_device(struct vga_device *vgadev) 
	if ((vgadev->owns & VGA_RSRC_LEGACY_MASK) == VGA_RSRC_LEGACY_MASK)

		return true;



	/*

	 * If we haven't found a legacy VGA device, accept a non-legacy

	 * device.  It may have either IO or MEM enabled, and bridges may

	 * not have PCI_BRIDGE_CTL_VGA enabled, so it may not be able to

	 * use legacy VGA resources.  Prefer an integrated GPU over others.

	 */

	pci_read_config_word(pdev, PCI_COMMAND, &cmd);

	if (cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY)) {



		/*

		 * An integrated GPU overrides a previous non-legacy

		 * device.  We expect only a single integrated GPU, but if

		 * there are more, we use the *last* because that was the

		 * previous behavior.

		 */

		if (vga_arb_integrated_gpu(&pdev->dev))

			return true;



		/*

		 * We prefer the first non-legacy discrete device we find.

		 * If we already found one, vgadev is no better.

		 */

		if (boot_vga) {

			pci_read_config_word(boot_vga->pdev, PCI_COMMAND,

					     &boot_cmd);

			if (boot_cmd & (PCI_COMMAND_IO | PCI_COMMAND_MEMORY))

				return false;

		}

		return true;

	}



	return false;

}
@@ -1529,30 +1561,8 @@ static struct miscdevice vga_arb_device = { 


static void __init vga_arb_select_default_device(void)

{

	struct pci_dev *pdev, *found = NULL;

	struct vga_device *vgadev;



	if (!vga_default_device()) {

		list_for_each_entry_reverse(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)) {

				found = pdev;

				if (vga_arb_integrated_gpu(dev))

					break;

			}

		}

	}



	if (found) {

		vgaarb_info(&found->dev, "setting as boot device (VGA legacy resources not available)\n");

		vga_set_default_device(found);

		return;

	}



	if (!vga_default_device()) {

		vgadev = list_first_entry_or_null(&vga_list,

						  struct vga_device, list);