[PATCH 1/2] drm/amdgpu: Add "max_bpc" connector property

[Kazlauskas, Nicholas]

On 11/7/18 10:40 AM, Deucher, Alexander wrote:
> FWIW there is a common property patch:
> 
> https://patchwork.kernel.org/patch/10606697/
> 
> When should try and be compatible so we can transition.
> 
> 
> Alex

Thanks for the heads up. I remember seeing the i915 patch but I missed 
the common property one. It's a shame that this isn't already in.

Sharing the same property name might work for compatibility ("max bpc").
The implementation relies on the same min/max range, the only thing that 
would change with that would be swapping out the attach with 
drm_connector_attach_max_bpc_property down the line.

> 
> ------------------------------------------------------------------------
> *From:* amd-gfx <amd-gfx-bounces at lists.freedesktop.org> on behalf of 
> Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
> *Sent:* Wednesday, November 7, 2018 9:56:54 AM
> *To:* amd-gfx at lists.freedesktop.org
> *Cc:* Kazlauskas, Nicholas
> *Subject:* [PATCH 1/2] drm/amdgpu: Add "max_bpc" connector property
> [Why]
> Many panels support more than 8bpc but some modes are unavailable while
> running at greater than 8bpc due to DP/HDMI bandwidth constraints.
> 
> Support for more than 8bpc was added recently in the driver but it's
> defaults to the maximum supported bpc - locking out these modes.
> 
> This should be a user configurable option such that the user can select
> what bpc configuration they would like.
> 
> [How]
> Introduce the "max_bpc" connector property so the user can limit the
> maximum bpc for the panel. It ranges from 8 to 16.
> 
> This doesn't directly set the preferred bpc for the panel but this
> convetion is already in use for other drivers.
> 
> Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
> ---
>   drivers/gpu/drm/amd/amdgpu/amdgpu_display.c | 5 +++++
>   drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h    | 2 ++
>   2 files changed, 7 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c 
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
> index 7d6a36bca9dd..83dadf5b85e0 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
> @@ -626,6 +626,11 @@ int amdgpu_display_modeset_create_props(struct 
> amdgpu_device *adev)
>                                            "dither",
>                                            amdgpu_dither_enum_list, sz);
> 
> +       adev->mode_info.max_bpc_property =
> +               drm_property_create_range(adev->ddev, 0, "max_bpc", 8, 16);
> +       if (!adev->mode_info.max_bpc_property)
> +               return -ENOMEM;
> +
>           if (amdgpu_device_has_dc_support(adev)) {
>                   adev->mode_info.freesync_property =
>                           drm_property_create_bool(adev->ddev, 0, 
> "freesync");
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h 
> b/drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h
> index 1627dd3413c7..c39af5d79608 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h
> @@ -338,6 +338,8 @@ struct amdgpu_mode_info {
>           struct drm_property *audio_property;
>           /* FMT dithering */
>           struct drm_property *dither_property;
> +       /* maximum number of bits per channel for monitor color */
> +       struct drm_property *max_bpc_property;
>           /* it is used to allow enablement of freesync mode */
>           struct drm_property *freesync_property;
>           /* it is used to know about display capability of freesync mode */
> -- 
> 2.17.1
> 
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Nicholas Kazlauskas