linux-kernel - Re: [PATCH 1/2] drm/msm/dsi: improve/fix dsc pclk calculation

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Message-ID: <e60361b2-29bc-aeee-2ab9-bb19e5c0afa6@marek.ca>
Date: Sat, 5 Oct 2024 12:55:10 -0400
From: Jonathan Marek <jonathan@...ek.ca>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
 freedreno@...ts.freedesktop.org
Cc: Rob Clark <robdclark@...il.com>, Abhinav Kumar
 <quic_abhinavk@...cinc.com>, Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Sean Paul <sean@...rly.run>, Marijn Suijten <marijn.suijten@...ainline.org>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Jessica Zhang <quic_jesszhan@...cinc.com>,
 Konrad Dybcio <konradybcio@...nel.org>,
 "open list:DRM DRIVER for Qualcomm display hardware"
 <linux-arm-msm@...r.kernel.org>,
 "open list:DRM DRIVER for Qualcomm display hardware"
 <dri-devel@...ts.freedesktop.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] drm/msm/dsi: improve/fix dsc pclk calculation

On 10/5/24 12:31 PM, Konrad Dybcio wrote:
> On 5.10.2024 4:38 PM, Jonathan Marek wrote:
>> drm_mode_vrefresh() can introduce a large rounding error, avoid it.
>>
>> Signed-off-by: Jonathan Marek <jonathan@...ek.ca>
>> ---
>>   drivers/gpu/drm/msm/dsi/dsi_host.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
>> index 185d7de0bf376..1205aa398e445 100644
>> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
>> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
>> @@ -542,7 +542,7 @@ static unsigned long dsi_adjust_pclk_for_compression(const struct drm_display_mo
>>   
>>   	int new_htotal = mode->htotal - mode->hdisplay + new_hdisplay;
>>   
>> -	return new_htotal * mode->vtotal * drm_mode_vrefresh(mode);
>> +	return mult_frac(mode->clock * 1000u, new_htotal, mode->htotal);
> 
> This seems to ignore mult/div by two on certain mode flags.. is that
> intended?
> 
> Konrad
> 

It is intended - those flags are not relevant to DSI panels, and DSC 
pclk adjustment is only about how DSC affects htotal.