linux-kernel - Re: [PATCH v3 2/4] drm/msm/dpu: Enable widebus for DSI INTF

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Date:   Thu, 17 Aug 2023 20:07:04 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Jessica Zhang <quic_jesszhan@...cinc.com>
Cc:     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>, quic_abhinavk@...cinc.com,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 2/4] drm/msm/dpu: Enable widebus for DSI INTF

On 08/08/2023 00:40, Jessica Zhang wrote:
> 
> 
> On 8/2/2023 11:20 AM, Dmitry Baryshkov wrote:
>> On Wed, 2 Aug 2023 at 21:09, Jessica Zhang <quic_jesszhan@...cinc.com> 
>> wrote:

>>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c 
>>> b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c
>>> index df88358e7037..dace6168be2d 100644
>>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c
>>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c
>>> @@ -69,8 +69,10 @@ static void _dpu_encoder_phys_cmd_update_intf_cfg(
>>>                                  phys_enc->hw_intf,
>>>                                  phys_enc->hw_pp->idx);
>>>
>>> -       if (intf_cfg.dsc != 0)
>>> +       if (intf_cfg.dsc != 0) {
>>>                  cmd_mode_cfg.data_compress = true;
>>> +               cmd_mode_cfg.wide_bus_en = 
>>> dpu_encoder_is_widebus_enabled(phys_enc->parent);
>>> +       }
>>
>> This embeds the knowledge that a wide bus can only be enabled when DSC
>> is in use. Please move the wide_bus_en assignment out of conditional
>> code.
> 
> Wide bus for DSI will only be enabled if DSC is enabled, so this is 
> technically not wrong, as DP will use the video mode path.
> 
>>
>>>
>>>          if (phys_enc->hw_intf->ops.program_intf_cmd_cfg)
>>>                  
>>> phys_enc->hw_intf->ops.program_intf_cmd_cfg(phys_enc->hw_intf, 
>>> &cmd_mode_cfg);
>>> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c 
>>> b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c
>>> index 8ec6505d9e78..dc6f3febb574 100644
>>> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c
>>> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c
>>> @@ -521,6 +521,9 @@ static void 
>>> dpu_hw_intf_program_intf_cmd_cfg(struct dpu_hw_intf *ctx,
>>
>> This function is only enabled for DPU >= 7.0, while IIRC wide bus can
>> be enabled even for some of the earlier chipsets.
> 
> The command mode path is only called for DSI, which only supports wide 
> bus for DPU 7.0+.

After second consideration, let's ignore this part, as wide bus will 
only be enabled for DSI / CMD after 7.0. If we ever have SoC that has 
CMD + wide_bus earlier than 5.0, we can reconsider this code pice.

Can you please add a comment that the register itself is present earlier 
(5.0), but it doesn't have to be programmed since the flags will not be 
set anyway.

> 
>>
>>>          if (cmd_mode_cfg->data_compress)
>>>                  intf_cfg2 |= INTF_CFG2_DCE_DATA_COMPRESS;
>>>
>>> +       if (cmd_mode_cfg->wide_bus_en)
>>> +               intf_cfg2 |= INTF_CFG2_DATABUS_WIDEN;
>>> +
>>>          DPU_REG_WRITE(&ctx->hw, INTF_CONFIG2, intf_cfg2);
>>>   }
>>>



-- 
With best wishes
Dmitry