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

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Message-ID: <81a5e241-ec82-7414-8752-4ce3cb084959@linaro.org>
Date:   Sat, 17 Jun 2023 03:35:42 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Marijn Suijten <marijn.suijten@...ainline.org>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>
Cc:     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 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.

>>
>> 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