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

[Dmitry Baryshkov]

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@xxxxxxxxxxx> 
> > 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