linux-kernel - Re: [PATCH 3/5] drm/msm/dpu: Check mode against PINGPONG or DSC max width

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Message-ID: <24e419da-71f8-4b0d-9416-0fe4c63eed0f@oss.qualcomm.com>
Date: Thu, 15 May 2025 17:39:06 -0700
From: Jessica Zhang <jessica.zhang@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
Cc: Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Abhinav Kumar <abhinav.kumar@....qualcomm.com>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] drm/msm/dpu: Check mode against PINGPONG or DSC max
 width



On 5/14/2025 5:28 PM, Dmitry Baryshkov wrote:
> On Wed, May 14, 2025 at 04:52:31PM -0700, Jessica Zhang wrote:
>> Validate requested mode and topology based on the PINGPONG or DSC encoder
>> max width. In addition, drop MAX_HDISPLAY_SPLIT and base LM reservation
>> off of PINGPONG or DSC encoder max width
> 
> Separate commit for num_lm, please.

Hi Dmitry,

Ack.

> 
>>
>> As noted in the patch, while DPU 8.x+ supports a max linewidth of 8960
>> for PINGPONG_0, there is some additional logic that needs to be added to
>> the resource manager to specifically try and reserve PINGPONG_0 for
>> modes that are greater than 5k.
>>
>> Since this is out of the scope of this series, add a helper that will
>> get the overall minimum PINGPONG max linewidth for a given chipset.
>>
>> Signed-off-by: Jessica Zhang <jessica.zhang@....qualcomm.com>
>> ---
>>   drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c | 46 +++++++++++++++++++++++++++-----
>>   1 file changed, 39 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
>> index 0714936d8835..6131d071b051 100644
>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
>> @@ -723,6 +723,31 @@ void dpu_crtc_complete_commit(struct drm_crtc *crtc)
>>   	_dpu_crtc_complete_flip(crtc);
>>   }
>>   
>> +static int msm_display_get_max_pingpong_width(struct dpu_kms *dpu_kms)
>> +{
>> +	const struct dpu_pingpong_cfg *pingpong;
>> +	u32 max_pingpong_width = dpu_kms->catalog->pingpong[0].max_linewidth;
>> +
>> +	/*
>> +	 * Find the smallest overall PINGPONG max_linewidth in the catalog since
>> +	 * max_linewidth can differ between PINGPONGs even within the same
>> +	 * chipset.
>> +	 *
>> +	 * Note: While, for DPU 8.x+, PINGPONG_0 can technically support up to
>> +	 * 8k resolutions, this requires reworking the RM to try to reserve
>> +	 * PINGPONG_0 for modes greater than 5k.
>> +	 *
>> +	 * Once this additional logic is implemented, we can drop this helper
>> +	 * and use the reserved PINGPONG's max_linewidth
>> +	 */
>> +	for (int i = 1; i < dpu_kms->catalog->pingpong_count; i++) {
>> +		pingpong = &dpu_kms->catalog->pingpong[i];
>> +		max_pingpong_width = min(max_pingpong_width, pingpong->max_linewidth);
>> +	}
> 
> Since we are skipping PINGPONG_0, wouldn't it be enough to return
> max_linewidth of PP_1 ?

I don't think we're skipping PINGPONG_0 here since `u32 
max_pingpong_width = dpu_kms->catalog->pingpong[0].max_linewidth;` at 
the top of the function.

> 
> I think, it would be easier to follow .max_dsc_encoder_width and store
> .max_pingpong_linewidth in dpu_caps (and later add special
> .max_pp0_linewidth).

Ack. I think my only concern for this is that max_pp0_linewidth won't be 
set for all chipsets. But if you're fine with that I'll go ahead and 
make this change.

Thanks,

Jessica Zhang

> 
>> +
>> +	return max_pingpong_width;
>> +}
>> +
>>   static int _dpu_crtc_check_and_setup_lm_bounds(struct drm_crtc *crtc,
>>   		struct drm_crtc_state *state)
>>   {
>