linux-kernel - Re: [PATCH] drm/msm/dp: fix the max supported bpp logic

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Message-ID: <5f2983ea-d694-44c3-8231-78c0de6db856@quicinc.com>
Date: Mon, 29 Jul 2024 11:38:27 -0700
From: Abhinav Kumar <quic_abhinavk@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: <freedreno@...ts.freedesktop.org>, Rob Clark <robdclark@...il.com>,
        "Sean
 Paul" <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        "David Airlie" <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>,
        Guenter
 Roeck <groeck@...omium.org>,
        Tanmay Shah <tanmay@...eaurora.org>,
        Vara Reddy
	<quic_varar@...cinc.com>,
        Stephen Boyd <swboyd@...omium.org>, <dri-devel@...ts.freedesktop.org>,
        <quic_jesszhan@...cinc.com>, <neil.armstrong@...aro.org>,
        <abel.vesa@...aro.org>, <quic_khsieh@...cinc.com>,
        Rob Clark <robdclark@...omium.org>,
        "Chandan
 Uddaraju" <chandanu@...eaurora.org>,
        <linux-arm-msm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/msm/dp: fix the max supported bpp logic



On 7/27/2024 5:51 AM, Dmitry Baryshkov wrote:
> On Fri, 26 Jul 2024 at 01:04, Abhinav Kumar <quic_abhinavk@...cinc.com> wrote:
>>
>> Currently the DP driver hard-codes the max supported bpp to 30.
>> This is incorrect because the number of lanes and max data rate
>> supported by the lanes need to be taken into account.
>>
>> Replace the hardcoded limit with the appropriate math which accounts
>> for the accurate number of lanes and max data rate.
>>
>> Fixes: c943b4948b58 ("drm/msm/dp: add displayPort driver support")
>> Signed-off-by: Abhinav Kumar <quic_abhinavk@...cinc.com>
>> ---
>>   drivers/gpu/drm/msm/dp/dp_panel.c | 7 +++++--
>>   1 file changed, 5 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/msm/dp/dp_panel.c b/drivers/gpu/drm/msm/dp/dp_panel.c
>> index a916b5f3b317..56ce5e4008f8 100644
>> --- a/drivers/gpu/drm/msm/dp/dp_panel.c
>> +++ b/drivers/gpu/drm/msm/dp/dp_panel.c
>> @@ -397,6 +397,7 @@ int dp_panel_init_panel_info(struct dp_panel *dp_panel)
>>   {
>>          struct drm_display_mode *drm_mode;
>>          struct dp_panel_private *panel;
>> +       u32 max_supported_bpp;
>>
>>          drm_mode = &dp_panel->dp_mode.drm_mode;
>>
>> @@ -423,8 +424,10 @@ int dp_panel_init_panel_info(struct dp_panel *dp_panel)
>>                                  drm_mode->clock);
>>          drm_dbg_dp(panel->drm_dev, "bpp = %d\n", dp_panel->dp_mode.bpp);
>>
>> -       dp_panel->dp_mode.bpp = max_t(u32, 18,
>> -                               min_t(u32, dp_panel->dp_mode.bpp, 30));
>> +       max_supported_bpp = dp_panel_get_mode_bpp(dp_panel, dp_panel->dp_mode.bpp,
>> +                                                 dp_panel->dp_mode.drm_mode.clock);
>> +       dp_panel->dp_mode.bpp = max_t(u32, 18, max_supported_bpp);
> 
> I think that in mode_valid() the driver should filter out modes that
> result in BPP being less than 18. Then the max_t can be dropped
> completely.
> 

With Stephen's suggested change, dp_panel_get_supported_bpp() will not 
return anything below min_supported_bpp which is 18 so we can absorb 
that part and drop the max_t part here.

> Nevertheless this indeed fixes an issue with the screen corruption,
> this is great!
> 
> Tested-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org> # SM8350-HDK
> 

Thanks for reporting and testing this. I need to give you Reported-by 
credits as well.

>> +
>>          drm_dbg_dp(panel->drm_dev, "updated bpp = %d\n",
>>                                  dp_panel->dp_mode.bpp);
>>
>> --
>> 2.44.0
>>
> 
>