Re: [PATCH v8 04/10] vgaarb: Move framebuffer detection to ADD_DEVICE path

[Huacai Chen <chenhuacai@gmail.com>]

Hi, Bjorn,

On Thu, Jan 6, 2022 at 8:07 AM Bjorn Helgaas <helgaas@kernel.org> wrote:
>
> From: Bjorn Helgaas <bhelgaas@google.com>
>
> Previously we selected a device that owns the boot framebuffer as the
> default device in vga_arb_select_default_device().  This was only done in
> the vga_arb_device_init() subsys_initcall, so devices enumerated later,
> e.g., by pcibios_init(), were not eligible.
>
> Fix this by moving the framebuffer 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.
>
> Note that if vga_arb_select_default_device() found a device owning the boot
> framebuffer, it unconditionally set it to be the default VGA device, and no
> subsequent device could replace it.
>
> Link: https://lore.kernel.org/r/20211015061512.2941859-7-chenhuacai@loongson.cn
> Based-on-patch-by: Huacai Chen <chenhuacai@loongson.cn>
> Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> Cc: Bruno Prémont <bonbons@linux-vserver.org>
> ---
>  drivers/gpu/vga/vgaarb.c | 37 +++++++++++++++++--------------------
>  1 file changed, 17 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
> index b0ae0f177c6f..aefa4f406f7d 100644
> --- a/drivers/gpu/vga/vgaarb.c
> +++ b/drivers/gpu/vga/vgaarb.c
> @@ -72,6 +72,7 @@ struct vga_device {
>         unsigned int io_norm_cnt;       /* normal IO count */
>         unsigned int mem_norm_cnt;      /* normal MEM count */
>         bool bridge_has_one_vga;
> +       bool is_framebuffer;    /* BAR covers firmware framebuffer */
>         unsigned int (*set_decode)(struct pci_dev *pdev, bool decode);
>  };
>
> @@ -565,10 +566,9 @@ void vga_put(struct pci_dev *pdev, unsigned int rsrc)
>  }
>  EXPORT_SYMBOL(vga_put);
>
> -static void __init vga_select_framebuffer_device(struct pci_dev *pdev)
> +static bool vga_is_framebuffer_device(struct pci_dev *pdev)
>  {
>  #if defined(CONFIG_X86) || defined(CONFIG_IA64)
> -       struct device *dev = &pdev->dev;
>         u64 base = screen_info.lfb_base;
>         u64 size = screen_info.lfb_size;
>         u64 limit;
> @@ -583,15 +583,6 @@ static void __init vga_select_framebuffer_device(struct pci_dev *pdev)
>
>         limit = base + size;
>
> -       /*
> -        * Override vga_arbiter_add_pci_device()'s I/O based detection
> -        * as it may take the wrong device (e.g. on Apple system under
> -        * EFI).
> -        *
> -        * Select the device owning the boot framebuffer if there is
> -        * one.
> -        */
> -
>         /* Does firmware framebuffer belong to us? */
>         for (i = 0; i < DEVICE_COUNT_RESOURCE; i++) {
>                 flags = pci_resource_flags(pdev, i);
> @@ -608,13 +599,10 @@ static void __init vga_select_framebuffer_device(struct pci_dev *pdev)
>                 if (base < start || limit >= end)
>                         continue;
>
> -               if (!vga_default_device())
> -                       vgaarb_info(dev, "setting as boot device\n");
> -               else if (pdev != vga_default_device())
> -                       vgaarb_info(dev, "overriding boot device\n");
> -               vga_set_default_device(pdev);
> +               return true;
>         }
>  #endif
> +       return false;
>  }
>
>  static bool vga_arb_integrated_gpu(struct device *dev)
> @@ -635,6 +623,7 @@ static bool vga_arb_integrated_gpu(struct device *dev)
>  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;
>
>         /*
>          * We select the default VGA device in this order:
> @@ -645,6 +634,18 @@ static bool vga_is_boot_device(struct vga_device *vgadev)
>          *   Other device (see vga_arb_select_default_device())
>          */
>
> +       /*
> +        * We always prefer a firmware framebuffer, so if we've already
> +        * found one, there's no need to consider vgadev.
> +        */
> +       if (boot_vga && boot_vga->is_framebuffer)
> +               return false;
> +
> +       if (vga_is_framebuffer_device(pdev)) {
> +               vgadev->is_framebuffer = true;
> +               return true;
> +       }
Maybe it is better to rename vga_is_framebuffer_device() to
vga_is_firmware_device() and rename is_framebuffer to
is_fw_framebuffer?

Huacai
> +
>         /*
>          * A legacy VGA device has MEM and IO enabled and any bridges
>          * leading to it have PCI_BRIDGE_CTL_VGA enabled so the legacy
> @@ -1531,10 +1532,6 @@ static void __init vga_arb_select_default_device(void)
>         struct pci_dev *pdev, *found = NULL;
>         struct vga_device *vgadev;
>
> -       list_for_each_entry(vgadev, &vga_list, list) {
> -               vga_select_framebuffer_device(vgadev->pdev);
> -       }
> -
>         if (!vga_default_device()) {
>                 list_for_each_entry_reverse(vgadev, &vga_list, list) {
>                         struct device *dev = &vgadev->pdev->dev;
> --
> 2.25.1
>