Re: [PATCH 2/3] drm/msm/dpu: Set DATABUS_WIDEN on command mode encoders

[Jessica Zhang]

On 6/16/2023 5:35 PM, Dmitry Baryshkov wrote:
> On 17/06/2023 00:54, Marijn Suijten wrote:
> > On 2023-06-16 14:18:39, Abhinav Kumar wrote:
> > > On 6/14/2023 12:56 AM, Dmitry Baryshkov wrote:
> > > > On 14/06/2023 04:57, Jessica Zhang wrote:
> > > > > Add a DPU INTF op to set the DATABUS_WIDEN register to enable the
> > > > > databus-widen mode datapath.
> > > > >
> > > > > Signed-off-by: Jessica Zhang <quic_jesszhan@xxxxxxxxxxx>
> > > > > ---
> > > > >    drivers/gpu/drm/msm/disp/dpu1/dpu_encoder_phys_cmd.c |  3 +++
> > > > >    drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c          | 12 
> > > > > ++++++++++++
> > > > >    drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.h          |  3 +++
> > > > >    3 files changed, 18 insertions(+)
> > > > >
> > > > > 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 b856c6286c85..124ba96bebda 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
> > > > > @@ -70,6 +70,9 @@ static void _dpu_encoder_phys_cmd_update_intf_cfg(
> > > > >        if (intf_cfg.dsc != 0 && 
> > > > > phys_enc->hw_intf->ops.enable_compression)
> > > > >            
> > > > > phys_enc->hw_intf->ops.enable_compression(phys_enc->hw_intf);
> > > > > +
> > > > > +    if (phys_enc->hw_intf->ops.enable_widebus)
> > > > > +        phys_enc->hw_intf->ops.enable_widebus(phys_enc->hw_intf);
> > > >
> > > > No. Please provide a single function which takes necessary
> > > > configuration, including compression and wide_bus_enable.
> > >
> > > There are two ways to look at this. Your point is coming from the
> > > perspective that its programming the same register but just a different
> > > bit. But that will also make it a bit confusing.
>
> My point is to have a high-level function that configures the INTF for 
> the CMD mode. This way it can take a structure with necessary 
> configuration bits.

Hi Dmitry,

After discussing this approach with Abhinav, we still have a few 
questions about it:

Currently, only 3 of the 32 bits for INTF_CONFIG2 are being used (the 
rest are reserved with no plans of being programmed in the future). Does 
this still justify the use of a struct to pass in the necessary 
configuration?

In addition, it seems that video mode does all its INTF_CONFIG2 
configuration separately in dpu_hw_intf_setup_timing_engine(). If we 
have a generic set_intf_config2() op, it might be good to have it as 
part of a larger cleanup where we have both video and command mode use 
the generic op. What are your thoughts on this?

Thanks,

Jessica Zhang

> > > So lets say the function is called intf_cfg2_xxx(..., bool widebus, bool
> > > data_compress)
> > >
> > > Now for the caller who wants to just enable widebus this will be
> > >
> > > intf_cfg2_xxx(....., true, false)
> > >
> > > if we want to do both
> > >
> > > intf_cfg2_xxx(...., true, true)
> > >
> > > the last one where we want to do just data_compress(highly unlikely and
> > > not recommended)
> > >
> > > intf_cfg2_xxx(...., false, true)
> > >
> > > Now someone looking at the code will have to go and find out what each
> > > bool is.
> > >
> > > Whereas with separate ops, its kind of implicit.
> >
> > That's why you never pass bools as function argument (edge-case if it is
> > the only argument, and its meaning becomes clear from the function
> > name).  Use enumerations anywhere else.
> >
> > - Marijn
> >
> > > For that reason, I dont think this patch is bad at all.
>
> --
> With best wishes
> Dmitry