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    Subject[PATCH v9 06/11] PCI/VGA: Move non-legacy VGA detection to ADD_DEVICE path
    Date
    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);
    --
    2.25.1
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