linux-kernel - Re: [Freedreno] [PATCH v9 3/5] drm/msm/dp: add support for DP PLL driver

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Date:   Tue, 11 Aug 2020 15:09:43 -0700
From:   Tanmay Shah <tanmay@...eaurora.org>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     David Airlie <airlied@...ux.ie>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        dri-devel <dri-devel@...ts.freedesktop.org>,
        Stephen Boyd <swboyd@...omium.org>, khsieh@...eaurora.org,
        Rob Clark <robdclark@...il.com>,
        Sean Paul <seanpaul@...omium.org>,
        Abhinav Kumar <abhinavk@...eaurora.org>,
        Daniel Vetter <daniel@...ll.ch>,
        Vara Reddy <varar@...eaurora.org>, aravindh@...eaurora.org,
        freedreno <freedreno@...ts.freedesktop.org>,
        Chandan Uddaraju <chandanu@...eaurora.org>
Subject: Re: [Freedreno] [PATCH v9 3/5] drm/msm/dp: add support for DP PLL
 driver

On 2020-08-11 13:21, Randy Dunlap wrote:
> On 8/11/20 12:49 PM, tanmay@...eaurora.org wrote:
>> On 2020-08-07 13:28, Randy Dunlap wrote:
>>> On 8/7/20 1:24 PM, Stephen Boyd wrote:
>>>> Quoting Rob Clark (2020-08-07 08:51:48)
>>>>> On Fri, Aug 7, 2020 at 8:27 AM Randy Dunlap <rdunlap@...radead.org>
>>>>> wrote:
>>>>>> 
>>>>>> On 8/7/20 12:17 AM, Tanmay Shah wrote:
>>>>>>> diff --git a/drivers/gpu/drm/msm/Kconfig 
>>>>>>> b/drivers/gpu/drm/msm/Kconfig
>>>>>>> index ea3c4d094d09..cc1392b29022 100644
>>>>>>> --- a/drivers/gpu/drm/msm/Kconfig
>>>>>>> +++ b/drivers/gpu/drm/msm/Kconfig
>>>>>>> @@ -60,6 +60,7 @@ config DRM_MSM_HDMI_HDCP
>>>>>>>  config DRM_MSM_DP
>>>>>>>       bool "Enable DP support in MSM DRM driver"
>>>>>>>       depends on DRM_MSM
>>>>>>> +     default y
>>>>>>>       help
>>>>>>>         Compile in support for DP driver in msm drm driver. DP 
>>>>>>> external
>>>>>>>         display support is enabled through this config option. It 
>>>>>>> can
>>>>>> 
>>>>>> Hi,
>>>>>> 
>>>>>> You need a very strong justification to make an optional part of a
>>>>>> driver
>>>>>> to be "default y".
>>>>> 
>>>>> My opinion is that if the driver is built, everything should be 
>>>>> built.
>>>>> This is what makes sense for distro's.  It is only the embedded 
>>>>> case
>>>>> where you want to trim down unneeded features where you might want 
>>>>> to
>>>>> disable some parts.  So 'default y' makes sense to me.
>>> 
>>> We don't set defaults for distro convenience.
>>> 
>>>> 
>>>> Maybe use 'default DRM_MSM' so that it doesn't trigger the 'default 
>>>> y'
>>>> filters people have?
>>> 
>>> Most people can figure that one out.  ;)
>>> I don't have any automated filters.
>> 
>> After after further reviews, I agree with Rob. Display Port is 
>> required module as of now so it makes sense to keep 'default y'.
> 
> If it is required, then you don't need to have a Kconfig entry/symbol 
> for it.

Kconfig makes driver flexible. Other moudles in the driver are also 
'default y' such as DSI. I will let Rob guide us further on this as he 
is the maintainer.