[PATCH RFC] drm/vc4: hdmi: Avoid ASoC error messages on startup

[Maxime Ripard]

On Mon, Jan 18, 2021 at 01:10:40PM +0100, Nicolas Saenz Julienne wrote:
> Hi Stefan, Maxime,
> 
> On Mon, 2021-01-18 at 12:28 +0100, Stefan Wahren wrote:
> > Hi,
> > 
> > Am 15.01.21 um 19:39 schrieb Mark Brown:
> > > On Fri, Jan 15, 2021 at 07:14:37PM +0100, Maxime Ripard wrote:
> > > > On Wed, Jan 13, 2021 at 11:42:23AM +0000, Mark Brown wrote:
> > > > > On Wed, Jan 13, 2021 at 10:19:57AM +0100, Maxime Ripard wrote:
> > > > > > I'd like to get Mark's opinion before merging though
> > > > > I'm not sure what the question is here?  I get CCed on a bunch of not
> > > > > obviously relevant DRM patches so there's a good chance I've just
> > > > > deleted some relevnat discussion.
> > > > The patch is question is here:
> > > > https://lore.kernel.org/dri-devel/1609256210-19863-1-git-send-email-stefan.wahren@i2se.com/
> > > > In particular, I'm not so sure whether it's fine to return -EPROBE_DEFER
> > > > in the startup hook.
> > > I wouldn't expect that to do anything useful and IIRC that error code
> > > will end up in userspace which isn't good.  If the driver wants to defer
> > > probe it should defer it from the probe() routine, after the driver has
> > > been instantiated I'm not sure what the expectation would be.  In
> > > general a driver should acquire all resources it needs when probing.
> > 
> > understand. Unfortunately, currently i don't have the time to
> > investigate how we can achieve this with this drm driver.
> > 
> > Maybe some else can take over?
> 
> My two cents: IIUC it's a tricky one since components don't have a way to
> express dependencies.

There's a way though :)

Components are bound in the order they've been added to the component
list, so as long as the component we have a dependency on is added
first, it's fine.

The issue here is that the HDMI devices are added first:
https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/vc4/vc4_drv.c#L334

We could just move the HDMI driver after the CRTC one and we would solve
it. I'm not sure if it has any other side effects though.

> Somewhat similar to what happened with the DSI bus/display race.

DSI is a bit different, especially on vc4 since the panel driver doesn't
sit on the DSI bus in DT and as such isn't added by the bus code when
the controller is added.

Maxime
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