From: Huacai Chen chenhuacai@loongson.cn
a37c0f48950b ("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 Signed-off-by: Huacai Chen chenhuacai@loongson.cn Cc: Daniel Axtens dja@axtens.net Cc: Zhou Wang wangzhou1@hisilicon.com --- drivers/pci/vgaarb.c | 54 ++++++++++++++++++++++++++------------------ 1 file changed, 32 insertions(+), 22 deletions(-)
diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c index c3323ab4f98e..e36ccbfdbd89 100644 --- a/drivers/pci/vgaarb.c +++ b/drivers/pci/vgaarb.c @@ -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);