linux-kernel - Re: [PATCH 1/4] drm/msm/dsi: Adjust pclk rate for compression

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Date:   Wed, 3 May 2023 10:10:11 -0700
From:   Jessica Zhang <quic_jesszhan@...cinc.com>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        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>,
        Marijn Suijten <marijn.suijten@...ainline.org>
CC:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        <linux-arm-msm@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <freedreno@...ts.freedesktop.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] drm/msm/dsi: Adjust pclk rate for compression



On 5/3/2023 1:33 AM, Dmitry Baryshkov wrote:
> On 03/05/2023 04:19, Jessica Zhang wrote:
>> Divide the pclk rate by the compression ratio when DSC is enabled
>>
>> Signed-off-by: Jessica Zhang <quic_jesszhan@...cinc.com>
>> ---
>>   drivers/gpu/drm/msm/dsi/dsi_host.c | 14 ++++++++++----
>>   1 file changed, 10 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c 
>> b/drivers/gpu/drm/msm/dsi/dsi_host.c
>> index 43a5ec33eee8..35c69dbe5f6f 100644
>> --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
>> +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
>> @@ -561,7 +561,8 @@ void dsi_link_clk_disable_v2(struct msm_dsi_host 
>> *msm_host)
>>       clk_disable_unprepare(msm_host->byte_clk);
>>   }
>> -static unsigned long dsi_get_pclk_rate(const struct drm_display_mode 
>> *mode, bool is_bonded_dsi)
>> +static unsigned long dsi_get_pclk_rate(const struct drm_display_mode 
>> *mode,
>> +        struct drm_dsc_config *dsc, bool is_bonded_dsi)
>>   {
>>       unsigned long pclk_rate;
>> @@ -576,6 +577,11 @@ static unsigned long dsi_get_pclk_rate(const 
>> struct drm_display_mode *mode, bool
>>       if (is_bonded_dsi)
>>           pclk_rate /= 2;
>> +    /* If DSC is enabled, divide pclk by compression ratio */
>> +    if (dsc)
>> +        pclk_rate = DIV_ROUND_UP(pclk_rate,
>> +                dsc->bits_per_component * 3 / msm_dsc_get_bpp_int(dsc));
>> +
> 
> Don't we loose precision here?
> Would DIV_ROUND_UP(pclk_rate * bpp, dsc->bpc * 3) be better?

Hi Dmitry,

Acked.

Thanks,

Jessica Zhang

> 
>>       return pclk_rate;
>>   }
>> @@ -585,7 +591,7 @@ unsigned long dsi_byte_clk_get_rate(struct 
>> mipi_dsi_host *host, bool is_bonded_d
>>       struct msm_dsi_host *msm_host = to_msm_dsi_host(host);
>>       u8 lanes = msm_host->lanes;
>>       u32 bpp = dsi_get_bpp(msm_host->format);
>> -    unsigned long pclk_rate = dsi_get_pclk_rate(mode, is_bonded_dsi);
>> +    unsigned long pclk_rate = dsi_get_pclk_rate(mode, msm_host->dsc, 
>> is_bonded_dsi);
>>       u64 pclk_bpp = (u64)pclk_rate * bpp;
>>       if (lanes == 0) {
>> @@ -604,7 +610,7 @@ unsigned long dsi_byte_clk_get_rate(struct 
>> mipi_dsi_host *host, bool is_bonded_d
>>   static void dsi_calc_pclk(struct msm_dsi_host *msm_host, bool 
>> is_bonded_dsi)
>>   {
>> -    msm_host->pixel_clk_rate = dsi_get_pclk_rate(msm_host->mode, 
>> is_bonded_dsi);
>> +    msm_host->pixel_clk_rate = dsi_get_pclk_rate(msm_host->mode, 
>> msm_host->dsc, is_bonded_dsi);
>>       msm_host->byte_clk_rate = dsi_byte_clk_get_rate(&msm_host->base, 
>> is_bonded_dsi,
>>                               msm_host->mode);
>> @@ -634,7 +640,7 @@ int dsi_calc_clk_rate_v2(struct msm_dsi_host 
>> *msm_host, bool is_bonded_dsi)
>>       dsi_calc_pclk(msm_host, is_bonded_dsi);
>> -    pclk_bpp = (u64)dsi_get_pclk_rate(msm_host->mode, is_bonded_dsi) 
>> * bpp;
>> +    pclk_bpp = (u64)dsi_get_pclk_rate(msm_host->mode, msm_host->dsc, 
>> is_bonded_dsi) * bpp;
>>       do_div(pclk_bpp, 8);
>>       msm_host->src_clk_rate = pclk_bpp;
>>
> 
> -- 
> With best wishes
> Dmitry
>