On 08/21/2014 11:41 AM, Boris BREZILLON wrote:
On Thu, 21 Aug 2014 11:04:07 +0200 Thierry Reding thierry.reding@gmail.com wrote:
On Thu, Aug 21, 2014 at 10:37:06AM +0200, Boris BREZILLON wrote:
Hi Ludovic,
On Thu, 21 Aug 2014 10:16:19 +0200 Ludovic Desroches ludovic.desroches@atmel.com wrote:
Hi Boris,
You can add
Tested-by: Ludovic Desroches ludovic.desroches@atmel.com
Thanks for testing this driver.
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.
I agree that deferring whole drm initialization due to panel not being ready is not an optimal solution. Nice solution of this problem is with DSI panels, DSI bus infrastructure provides callbacks for DRM encoder which are called when DSI panel is ready. Simple panels are platform devices so they do not have such callbacks. To solve this in a generic way I have proposed framework for tracking interfaces[1], the series contains also solution for the same problem with exynos display controller[2].
Regards Andrzej
[1]: https://lkml.org/lkml/2014/4/30/345 [2]: https://lkml.org/lkml/2014/4/30/653
That will still cause some delay before everything gets set up, but hopefully less than what you're seeing now. There's also another thread where this is being discussed because deferred probing is causing "unacceptable" delays as well.
Could you point this thread out to me please ?
Best Regards,
Boris