Message-ID: <3zsfsfsgegwbfg5wi53z2mwfevqlubfj4ddxwvmpzu4kgezvdj@knhggjm4gbmu>
Date:   Wed, 21 Jun 2023 21:00:54 +0200
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Jessica Zhang <quic_jesszhan@...cinc.com>,
        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 2023-06-21 19:36:37, Dmitry Baryshkov wrote:
> On 21/06/2023 18:17, Marijn Suijten wrote:
> > On 2023-06-20 14:38:34, Jessica Zhang wrote:
> > <snip>
> >>>>>>> +    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?
> > 
> > No.  The point Dmitry is making is **not** about this concidentally
> > using the same register, but about adding a common codepath to enable
> > compression on this hw_intf (regardless of the registers it needs to
> > touch).
> 
> Actually to setup INTF for CMD stream (which is equal to setting up 
> compression at this point).

Yup, thaty is what I suggested below ("or even more generically").

> >  Similar to how dpu_hw_intf_setup_timing_engine() programs the
> > hw_intf - including widebus! - for video-mode.
> > 
> > Or even more generically, have a struct similar to intf_timing_params
> > that says how the intf needs to be configured - without the caller
> > knowing about INTF_CONFIG2.
> > 
> > struct dpu_hw_intf_cfg is a very good example of how we can use a single
> > struct and a single callback to configure multiple registers at once
> > based on some input parameters.
> > 
> >> 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?
> > 
> > Not in that way, but if there is a generic enable_compression() or
> > configure_compression() callback (or even more generic, similar to
> > setup_intf_cfg in dpu_hw_ctl) that would work for both video-mode and
> > command-mode, maybe that is beneficial.
> 
> I'd rather not do this. Let's just 'setup timing enging' vs 'setup CMD'. 
> For example, it might also include setting up other INTF parameters for 
> CMD mode (if anything is required later on).

Sure, sounds good.  hw_intf internally could even have a static function
that deduplicates these "setup" function if there is any.

We could rename setup_timing_engine to setup_video_mode to be more clear
to the reader?

- Marijn

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