linux-kernel - Re: [PATCH v3] drm/display: Select DP helper for DRM_DP_AUX_CHARDEV and DRM_DP

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Message-ID: <8181a700-4955-cbdb-553f-311d790c603f@redhat.com>
Date:   Thu, 28 Apr 2022 11:11:36 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Lyude Paul <lyude@...hat.com>
Cc:     David Airlie <airlied@...ux.ie>, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v3] drm/display: Select DP helper for DRM_DP_AUX_CHARDEV
 and DRM_DP_CEC

On 4/28/22 10:42, Thomas Zimmermann wrote:
> Hi
> 

[snip]

>>   drivers/gpu/drm/display/Kconfig | 6 ++++--
>>   1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/display/Kconfig b/drivers/gpu/drm/display/Kconfig
>> index f84f1b0cd23f..1b6e6af37546 100644
>> --- a/drivers/gpu/drm/display/Kconfig
>> +++ b/drivers/gpu/drm/display/Kconfig
>> @@ -31,7 +31,8 @@ config DRM_DISPLAY_HDMI_HELPER
>>   
>>   config DRM_DP_AUX_CHARDEV
>>   	bool "DRM DP AUX Interface"
>> -	depends on DRM
>> +	depends on DRM && DRM_DISPLAY_HELPER
>> +	select DRM_DISPLAY_DP_HELPER
>

My rationale was that since DRM_DISPLAY_DP_HELPER is not a user-visible
symbol but DRM_DP_{AUX_CHARDEV,CEC} are, the latter should be able to
be enabled by the user without relying on other drivers to select the
required symbols (I would argue that even should select DP_HELPER but
that can't be done or otherwise the helper couldn't be built as module).

In other words, either DRM_DP_{AUX_CHARDEV,CEC} can be user selectable
as a standalone symbol or can't and will only be visible if other driver
selects their required symbols.

In which case, why not just do this non-user visible and just make the
drivers using their helpers to select it directly? That is one of the
options I proposed before.

So I believe this is the less intrusive change that will preserve the
current behaviour as much as possible.

I don't have a strong opinion though and if you prefer I can change to
be a depends instead.

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat