linux-kernel - Re: [PATCH v2 4/7] drm/i915/display: Add handling for new "active bpc" property

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Date:   Thu, 10 Jun 2021 14:50:36 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Werner Sembach <wse@...edocomputers.com>
Cc:     harry.wentland@....com, sunpeng.li@....com,
        alexander.deucher@....com, christian.koenig@....com,
        airlied@...ux.ie, daniel@...ll.ch,
        maarten.lankhorst@...ux.intel.com, tzimmermann@...e.de,
        jani.nikula@...ux.intel.com, joonas.lahtinen@...ux.intel.com,
        rodrigo.vivi@...el.com, amd-gfx@...ts.freedesktop.org,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org
Subject: Re: [PATCH v2 4/7] drm/i915/display: Add handling for new "active
 bpc" property

Hi

On Tue, Jun 08, 2021 at 07:43:17PM +0200, Werner Sembach wrote:
> This commits implements the "active bpc" drm property for the Intel GPU driver.
> 
> Signed-off-by: Werner Sembach <wse@...edocomputers.com>
> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 14 ++++++++++++++
>  drivers/gpu/drm/i915/display/intel_dp.c      |  8 ++++++--
>  drivers/gpu/drm/i915/display/intel_dp_mst.c  |  4 +++-
>  drivers/gpu/drm/i915/display/intel_hdmi.c    |  4 +++-
>  4 files changed, 26 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 64e9107d70f7..50c11b8770a7 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -10388,6 +10388,9 @@ static int intel_atomic_commit(struct drm_device *dev,
>  {
>  	struct intel_atomic_state *state = to_intel_atomic_state(_state);
>  	struct drm_i915_private *dev_priv = to_i915(dev);
> +	struct drm_connector *connector;
> +	struct drm_connector_state *new_conn_state;
> +	int i;
>  	int ret = 0;
>  
>  	state->wakeref = intel_runtime_pm_get(&dev_priv->runtime_pm);
> @@ -10456,6 +10459,17 @@ static int intel_atomic_commit(struct drm_device *dev,
>  	intel_shared_dpll_swap_state(state);
>  	intel_atomic_track_fbs(state);
>  
> +	/* Extract information from crtc to communicate it to userspace as connector properties */
> +	for_each_new_connector_in_state(&state->base, connector, new_conn_state, i) {
> +		struct intel_crtc *crtc = to_intel_crtc(new_conn_state->crtc);
> +		if (crtc) {
> +			struct intel_crtc_state *new_crtc_state = intel_atomic_get_new_crtc_state(state, crtc);
> +			new_conn_state->active_bpc = new_crtc_state->pipe_bpp / 3;
> +		}
> +		else
> +			new_conn_state->active_bpc = 0;
> +	}
> +

This seems fairly intrusive, but also commit / commit_tail might not be
the best place to put this, we want to support it at the connector
level.

Indeed, this will cause some issue if your HDMI output is a bridge for
example, where the commit will be in an entirely different driver that
has no dependency on the HDMI controller one.

I think it would be best to do that assignment in atomic_check. That
way, if the userspace does a commit with DRM_MODE_ATOMIC_TEST_ONLY it
would know what the output state would have been like.

Also, all of your patches don't follow the kernel coding style. Make
sure you fix the issues reported by checkpatch --strict

Maxime

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