Re: [PATCH 2/3] drm/vc4: Don't try to initialize FBDEV if we're only bound to V3D.

[Daniel Vetter]

On Wed, Apr 19, 2017 at 7:55 PM, Eric Anholt <eric@xxxxxxxxxx> wrote:
> Daniel Vetter <daniel@xxxxxxxx> writes:
>> On Tue, Apr 18, 2017 at 9:11 PM, Eric Anholt <eric@xxxxxxxxxx> wrote:
>>> The FBDEV initialization would throw an error in dmesg, when we just
>>> want to silently not initialize fbdev on a V3D-only VC4 instance.
>>>
>>> Signed-off-by: Eric Anholt <eric@xxxxxxxxxx>
>>
>> Hm, this shouldn't be an error really, you might want to hotplug more
>> connectors later on. What exactly complains?
>
> drm_fb_helper_init() throws an error if the passed in connector count is
> 0, so drm_fb_cma_helper() printks an error.

Oh, _that_ thing. The error in there is correct, but (almost) everyone
gets this parameter wrong. This isn't the max number of connectors the
fb helper will light up, but just the max number of connectors _per_
crtc when driving in hw clone mode. There's two problems with that:
- fb helpers don't support hw clone mode, we select 1:1 crtcs for each
active connector
- I mentioned that everyone gets this wrong?

If you're moderately bored it'd be great to nuke the max_connector
argument from drm_fb_helper_init, and hard-code it to 1 (with a big
comment explaining that this needs to be changed, probably with
dynamic reallocation, once someone gets around to implementing hw
clone mode).

If you're less bored, just hardcode this to 1 in vc4 and done. Plus a
TODO.rst entry would be great in that case.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch