linux-kernel - Re: [PATCH 2/3] drm/msm/dpu: Set DATABUS

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Message-ID: <CAA8EJpoW_QBqti3e8Aji5JpKA9LhnTCy+tHZD-Et1aFbWabubw@mail.gmail.com>
Date:   Wed, 21 Jun 2023 01:10:07 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Jessica Zhang <quic_jesszhan@...cinc.com>
Cc:     Marijn Suijten <marijn.suijten@...ainline.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] drm/msm/dpu: Set DATABUS_WIDEN on command mode encoders

On Wed, 21 Jun 2023 at 00:38, Jessica Zhang <quic_jesszhan@...cinc.com> wrote:
>
>
>
> 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@...cinc.com>
> >>>>> ---
> >>>>>    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?

Yes.

>
> 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?

No. If I get your idea right, this would mean moving INTF_CONFIG2
knowledge to the caller, which, I think, is a bad idea.

>
> 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
> >



-- 
With best wishes
Dmitry