On Thu, 21 Aug 2014 11:52:03 +0200
Thierry Reding [off-list ref] wrote:

On Thu, Aug 21, 2014 at 11:41:59AM +0200, Boris BREZILLON wrote:

quoted

On Thu, 21 Aug 2014 11:04:07 +0200
Thierry Reding [off-list ref] wrote:

quoted

On Thu, Aug 21, 2014 at 10:37:06AM +0200, Boris BREZILLON wrote:

quoted

Hi Ludovic,

On Thu, 21 Aug 2014 10:16:19 +0200
Ludovic Desroches [off-list ref] wrote:

quoted

Hi Boris,

You can add

Tested-by: Ludovic Desroches <redacted>

Thanks for testing this driver.

quoted

Only one issue but not related to your patches, you can't display
quickly the bootup logo since the panel detection takes too much
time.

Yes, actually this is related to the device probe order: the
hlcdc-display-controller device is probed before the simple-panel, thus
nothing is detected on the RGB connector (I use of_drm_find_panel to
check for panel availability) when the display controller is
instantiated. I rely on the default polling infrastructure provided by
the DRM/KMS framework which polls for a new connector every 10s, and
this is far more than you kernel boot time.

Do anyone see a solution to reduce this delay (without changing the
polling interval). I thought we could add a notifier infrastructure to
the DRM panel framework, but I'm not sure this is how you want things
done...

Other drivers return -EPROBE_DEFER when a panel hasn't been registered
yet. This will automatically take care of ordering things in a way that
DRM/KMS will only be initialized after the panel has been probed.

Actually I'd like to avoid doing this with a deferred probe, because,
AFAIU, the remote endpoint is not tightly linked with the display
controller driver (I mean the display controller can still be
initialized without having a display connected on it).
Moreover the atmel dev kit I'm using has an HDMI bridge connected on
the same RGB connector and I'd like to use it in a near future.
Returning -EPROBE_DEFER in case of several devices connected on the
same connector implies that I'll have to wait for all the remote
end-points to be available before my display controller could be
instantiated.

While this could be acceptable when all drivers are statically linked
in the kernel, it might be problematic when you're using modules,
meaning that you won't be able to display anything on your LCD panel
until your HDMI bridge module has been loaded.

No. HDMI should be using proper hotplugging anyway, hence it should be
always be loaded anyway. You're in for a world of pain if you think you
can run DRM with a driver that's composed of separate kernel modules.

I was talking about the external RGB to HDMI encoder, should the driver
for this encoder (which is not on On Chip block) be compiled
statically too ?

Also if you don't want to use deferred probe, then you're in for the
full hotplugging panel dance and that implies that you need to fix a
bunch of things in DRM (one being the framebuffer console instantiation
that I referred to in the other thread).

For now, I wait until there is a device connected on the RGB connector
(connector status set to connector_status_connected) before creating an
fbdev. It might not be the cleanest way to solve this issue, but it
works :-).

You also can't be using the
current device tree bindings because they all assume a dependency from
the display controller/output to the panel. For hotplugging you'd need
the dependency the other way around (the panel needs to refer to the
output by phandle).

Here [1] is a proposal for notification support in the drm_panel
infrastructure (which is not that complicated), and here [2] is how
I use it in my atmel-hlcdc driver to generate hotplug events.

Let me know if you want me to submit a proper patch series...

Best Regards,

Boris

[1]http://code.bulix.org/scq4g3-86804
[2]http://code.bulix.org/7dg501-86805

-- 
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com