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From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Wed, 19 May 2021 12:45:18 -0400
Message-ID: <CADnq5_OstgUmLxa4DU2s19m5E1zScKY0Pe=644BvBTp=LAPvJg@mail.gmail.com>
Subject: Re: [PATCH] vgaarb: Use ACPI HID name to find integrated GPU
To:     Kai-Heng Feng <kai.heng.feng@canonical.com>
Cc:     Dave Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
        Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        "Deucher, Alexander" <alexander.deucher@amd.com>,
        open list <linux-kernel@vger.kernel.org>,
        "open list:DRM DRIVERS" <dri-devel@lists.freedesktop.org>
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On Wed, May 19, 2021 at 9:57 AM Kai-Heng Feng
<kai.heng.feng@canonical.com> wrote:
>
> Commit 3d42f1ddc47a ("vgaarb: Keep adding VGA device in queue") assumes
> the first device is an integrated GPU. However, on AMD platforms an
> integrated GPU can have higher PCI device number than a discrete GPU.
>
> Integrated GPU on ACPI platform generally has _DOD and _DOS method, so
> use that as predicate to find integrated GPU. If the new strategy
> doesn't work, fallback to use the first device as boot VGA.
>
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>

Unless there are any other comments, I'll apply it tomorrow.

Alex

> ---
>  drivers/gpu/vga/vgaarb.c | 31 ++++++++++++++++++++++++++-----
>  1 file changed, 26 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/vga/vgaarb.c b/drivers/gpu/vga/vgaarb.c
> index 5180c5687ee5..949fde433ea2 100644
> --- a/drivers/gpu/vga/vgaarb.c
> +++ b/drivers/gpu/vga/vgaarb.c
> @@ -50,6 +50,7 @@
>  #include <linux/screen_info.h>
>  #include <linux/vt.h>
>  #include <linux/console.h>
> +#include <linux/acpi.h>
>
>  #include <linux/uaccess.h>
>
> @@ -1450,9 +1451,23 @@ static struct miscdevice vga_arb_device = {
>         MISC_DYNAMIC_MINOR, "vga_arbiter", &vga_arb_device_fops
>  };
>
> +#if defined(CONFIG_ACPI)
> +static bool vga_arb_integrated_gpu(struct device *dev)
> +{
> +       struct acpi_device *adev = ACPI_COMPANION(dev);
> +
> +       return adev && !strcmp(acpi_device_hid(adev), ACPI_VIDEO_HID);
> +}
> +#else
> +static bool vga_arb_integrated_gpu(struct device *dev)
> +{
> +       return false;
> +}
> +#endif
> +
>  static void __init vga_arb_select_default_device(void)
>  {
> -       struct pci_dev *pdev;
> +       struct pci_dev *pdev, *found = NULL;
>         struct vga_device *vgadev;
>
>  #if defined(CONFIG_X86) || defined(CONFIG_IA64)
> @@ -1505,20 +1520,26 @@ static void __init vga_arb_select_default_device(void)
>  #endif
>
>         if (!vga_default_device()) {
> -               list_for_each_entry(vgadev, &vga_list, list) {
> +               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)) {
> -                               vgaarb_info(dev, "setting as boot device (VGA legacy resources not available)\n");
> -                               vga_set_default_device(pdev);
> -                               break;
> +                               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);
> --
> 2.31.1
>