From: Huacai Chen <chenhuacai@xxxxxxxxxxx>
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@xxxxxxxxxxx
[bhelgaas: commit log, restructure]
Link: https://lore.kernel.org/r/20211015061512.2941859-5-chenhuacai@xxxxxxxxxxx
Link: https://lore.kernel.org/r/20211015061512.2941859-7-chenhuacai@xxxxxxxxxxx
Signed-off-by: Huacai Chen <chenhuacai@xxxxxxxxxxx>
Cc: Daniel Axtens <dja@xxxxxxxxxx>
Cc: Zhou Wang <wangzhou1@xxxxxxxxxxxxx>
---
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);
--
2.25.1
