[PATCH v3] drm/amd: Fail initialization earlier when DC is disabled

[Alex Deucher]

On Thu, Mar 6, 2025 at 3:51 PM Mario Limonciello
<mario.limonciello at amd.com> wrote:
>
> Modern APU and dGPU require DC support to be able to light up the
> display.  If DC support has been disabled either by kernel config
> or by kernel command line the screen will visibly freeze when the
> driver finishes early init.
>
> As it's known before early init is done whether DC support is required
> detect this during discovery and bail if DC support was disabled
> for any reason.  This will ensure that the existing framebuffer
> provided by efifb or simpledrm keeps working.
>
> Signed-off-by: Mario Limonciello <mario.limonciello at amd.com>
> ---
> v3:
>  * Use amdgpu_device_asic_has_dc_support() instead to cover virtual
>    displays and bringup
> v2:
>  * Update commit message justification
>  * Add correct "default" handling
> ---
>  drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c | 49 ++++++++++++++-----
>  1 file changed, 36 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
> index a4258127083d0..ddd10e6345601 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_discovery.c
> @@ -2134,15 +2134,14 @@ static void amdgpu_discovery_set_sriov_display(struct amdgpu_device *adev)
>
>  static int amdgpu_discovery_set_display_ip_blocks(struct amdgpu_device *adev)
>  {
> +       bool asic_support;
> +
>         if (adev->enable_virtual_display) {
>                 amdgpu_device_ip_block_add(adev, &amdgpu_vkms_ip_block);
>                 return 0;
>         }

I think this will break for chips with harvested DCN blocks.  I think
you need to return early here in that case.  E.g.,

if (adev->harvest_ip_mask & AMD_HARVEST_IP_DMU_MASK)
    return 0;

Alex

>
> -       if (!amdgpu_device_has_dc_support(adev))
> -               return 0;
> -
> -#if defined(CONFIG_DRM_AMD_DC)
> +       asic_support = amdgpu_device_asic_has_dc_support(adev->asic_type);
>         if (amdgpu_ip_version(adev, DCE_HWIP, 0)) {
>                 switch (amdgpu_ip_version(adev, DCE_HWIP, 0)) {
>                 case IP_VERSION(1, 0, 0):
> @@ -2166,39 +2165,63 @@ static int amdgpu_discovery_set_display_ip_blocks(struct amdgpu_device *adev)
>                 case IP_VERSION(3, 5, 1):
>                 case IP_VERSION(3, 6, 0):
>                 case IP_VERSION(4, 1, 0):
> +                       if (!asic_support) {
> +                               dev_err(adev->dev,
> +                                       "DC support is required for dm ip block(DCE_HWIP:0x%x)\n",
> +                                       amdgpu_ip_version(adev, DCE_HWIP, 0));
> +                               return -EINVAL;
> +                       }
> +
>                         /* TODO: Fix IP version. DC code expects version 4.0.1 */
>                         if (adev->ip_versions[DCE_HWIP][0] == IP_VERSION(4, 1, 0))
>                                 adev->ip_versions[DCE_HWIP][0] = IP_VERSION(4, 0, 1);
>
> +#if defined(CONFIG_DRM_AMD_DC)
>                         if (amdgpu_sriov_vf(adev))
>                                 amdgpu_discovery_set_sriov_display(adev);
>                         else
>                                 amdgpu_device_ip_block_add(adev, &dm_ip_block);
>                         break;
> +#endif
>                 default:
> -                       dev_err(adev->dev,
> -                               "Failed to add dm ip block(DCE_HWIP:0x%x)\n",
> -                               amdgpu_ip_version(adev, DCE_HWIP, 0));
> -                       return -EINVAL;
> +                       if (asic_support) {
> +                               dev_err(adev->dev,
> +                                       "Failed to add dm ip block(DCE_HWIP:0x%x)\n",
> +                                       amdgpu_ip_version(adev, DCE_HWIP, 0));
> +                               return -EINVAL;
> +                       }
> +                       return 0;
>                 }
>         } else if (amdgpu_ip_version(adev, DCI_HWIP, 0)) {
>                 switch (amdgpu_ip_version(adev, DCI_HWIP, 0)) {
>                 case IP_VERSION(12, 0, 0):
>                 case IP_VERSION(12, 0, 1):
>                 case IP_VERSION(12, 1, 0):
> +
> +                       if (!asic_support) {
> +                               dev_err(adev->dev,
> +                                       "DC support is required for dm ip block(DCI_HWIP:0x%x)\n",
> +                                       amdgpu_ip_version(adev, DCI_HWIP, 0));
> +                               return -EINVAL;
> +                       }
> +
> +#if defined(CONFIG_DRM_AMD_DC)
>                         if (amdgpu_sriov_vf(adev))
>                                 amdgpu_discovery_set_sriov_display(adev);
>                         else
>                                 amdgpu_device_ip_block_add(adev, &dm_ip_block);
>                         break;
> +#endif
>                 default:
> -                       dev_err(adev->dev,
> -                               "Failed to add dm ip block(DCI_HWIP:0x%x)\n",
> -                               amdgpu_ip_version(adev, DCI_HWIP, 0));
> -                       return -EINVAL;
> +                       if (asic_support) {
> +                               dev_err(adev->dev,
> +                                       "Failed to add dm ip block(DCI_HWIP:0x%x)\n",
> +                                       amdgpu_ip_version(adev, DCI_HWIP, 0));
> +                               return -EINVAL;
> +                       }
> +                       return 0;
>                 }
>         }
> -#endif
>         return 0;
>  }
>
> --
> 2.43.0
>