linux-kernel - Re: [RFC PATCH 02/11] drm/fb-helper: Skip writeback connectors

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Message-ID: <20161011164751.GB14337@e106950-lin.cambridge.arm.com>
Date:   Tue, 11 Oct 2016 17:47:52 +0100
From:   Brian Starkey <brian.starkey@....com>
To:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        linux-media@...r.kernel.org, liviu.dudau@....com,
        robdclark@...il.com, hverkuil@...all.nl, eric@...olt.net,
        ville.syrjala@...ux.intel.com
Subject: Re: [RFC PATCH 02/11] drm/fb-helper: Skip writeback connectors

On Tue, Oct 11, 2016 at 05:44:48PM +0200, Daniel Vetter wrote:
>On Tue, Oct 11, 2016 at 03:53:59PM +0100, Brian Starkey wrote:
>> Writeback connectors aren't much use to the fbdev helpers, as they won't
>> show anything to the user. Skip them when looking for candidate output
>> configurations.
>>
>> Signed-off-by: Brian Starkey <brian.starkey@....com>
>> ---
>>  drivers/gpu/drm/drm_fb_helper.c |    4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
>> index 03414bd..dedf6e7 100644
>> --- a/drivers/gpu/drm/drm_fb_helper.c
>> +++ b/drivers/gpu/drm/drm_fb_helper.c
>> @@ -2016,6 +2016,10 @@ static int drm_pick_crtcs(struct drm_fb_helper *fb_helper,
>>  	if (modes[n] == NULL)
>>  		return best_score;
>>
>> +	/* Writeback connectors aren't much use for fbdev */
>> +	if (connector->connector_type == DRM_MODE_CONNECTOR_WRITEBACK)
>> +		return best_score;
>
>I think we could handle this by always marking writeback connectors as
>disconnected. Userspace and fbdev emulation should then avoid them,
>always.
>-Daniel
>

Good idea; I'll need to take a closer look at how it would interact
with the probe helper (connector->force etc).

Are you thinking instead-of or in-addition-to the client cap? I'd be
worried about apps doing strange things and trying to use even
disconnected connectors.

>> +
>>  	crtcs = kzalloc(fb_helper->connector_count *
>>  			sizeof(struct drm_fb_helper_crtc *), GFP_KERNEL);
>>  	if (!crtcs)
>> --
>> 1.7.9.5
>>
>
>-- 
>Daniel Vetter
>Software Engineer, Intel Corporation
>http://blog.ffwll.ch
>