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

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
Link: https://lore.kernel.org/r/20220224224753.297579-7-helgaas@kernel.org
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: Daniel Axtens <dja@axtens.net>
Cc: Zhou Wang <wangzhou1@hisilicon.com>

diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
index c3323ab4f98eb798d40d7cb0e3b630be04b98788..e36ccbfdbd89413a4a9e12f9009bcc55a9b2e683 100644 (file)
--- 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);