linux-kernel - Re: [PATCH 02/11] drm/msm/dpu: use the actual lm maximum width instead of a hardcoded value

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Date:   Thu, 20 Apr 2023 01:23:52 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Arnaud Vrac <avrac@...ebox.fr>, Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Cc:     linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 02/11] drm/msm/dpu: use the actual lm maximum width
 instead of a hardcoded value

On 19/04/2023 17:41, Arnaud Vrac wrote:
> This avoids using two LMs instead of one when the display width is lower
> than the maximum supported value. For example on MSM8996/MSM8998, the
> actual maxwidth is 2560, so we would use two LMs for 1280x720 or
> 1920x1080 resolutions, while one is enough.
> 
> Signed-off-by: Arnaud Vrac <avrac@...ebox.fr>

While this looks correct (and following what we have in 4.4), later 
vendor kernels specify the topology explicitly. Probably we should check 
this with the hw guys, because it might be the following case: even 
though a single LM can supply the mode, it will spend more power 
compared to two LMs.


> ---
>   drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c | 10 +++++-----
>   1 file changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> index 1dc5dbe585723..dd2914726c4f6 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder.c
> @@ -53,8 +53,6 @@
>   
>   #define IDLE_SHORT_TIMEOUT	1
>   
> -#define MAX_HDISPLAY_SPLIT 1080
> -
>   /* timeout in frames waiting for frame done */
>   #define DPU_ENCODER_FRAME_DONE_TIMEOUT_FRAMES 5
>   
> @@ -568,10 +566,12 @@ static struct msm_display_topology dpu_encoder_get_topology(
>   	 */
>   	if (intf_count == 2)
>   		topology.num_lm = 2;
> -	else if (!dpu_kms->catalog->caps->has_3d_merge)
> -		topology.num_lm = 1;
> +	else if (dpu_kms->catalog->caps->has_3d_merge &&
> +		 dpu_kms->catalog->mixer_count > 0 &&
> +		 mode->hdisplay > dpu_kms->catalog->mixer[0].sblk->maxwidth)
> +		topology.num_lm = 2;
>   	else
> -		topology.num_lm = (mode->hdisplay > MAX_HDISPLAY_SPLIT) ? 2 : 1;
> +		topology.num_lm = 1;
>   
>   	if (crtc_state->ctm)
>   		topology.num_dspp = topology.num_lm;
> 

-- 
With best wishes
Dmitry