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

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Message-ID: <n2c5qlujxhbbj2aqlgj7fetzoteood5h4hmbwt4mapi77xlvmt@bpourzaideti>
Date:   Fri, 16 Jun 2023 23:54:46 +0200
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Jessica Zhang <quic_jesszhan@...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 2023-06-16 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.
> 
> 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.