Re: DRM interaction problems on Ingenic CI20 / jz4780 with dw-hdmi and ingenic-drm

[Paul Cercueil <paul@crapouillou.net>]

Hi Nikolaus,

So I just wrote a HDMI driver for a different chip, I guess I can 
answer some of your questions now.


Le lun. 13 avril 2020 à 13:25, Paul Cercueil <paul@crapouillou.net> a 
écrit :
> Hi Nikolaus,
> 
> 
> Le sam. 11 avril 2020 à 16:14, H. Nikolaus Schaller 
> <hns@goldelico.com> a écrit :
>> Hi,
>> we (Paul Boddie and me) are working to get HDMI functional on the
>> Ingenic CI20 board with jz4780 SoC which uses a specialization of
>> the dw-hdmi driver.
>> 
>> 
>> So far we have identified two issues.
>> 
>> The first is that HPD interrupts are not properly processed.
>> 
>> drm_helper_hpd_irq_event() is called by HPD events but
>> dev->mode_config.poll_enabled is false.
>> 

This is to be used when there's no hardware interrupt. I believe you 
have one, right? Then call drm_kms_helper_hotplug_event() from the 
interrupt handler instead.

>> Therefore the interrupt is ignored and nothing happens.
>> 
>> Now I wonder about the logic behind checking for poll_enabled.
>> I understand that a driver can do either polling or irq or both.
>> 
>> Therefore handling the irq_event shouldn't be disabled by 
>> poll_enabled
>> being false. Otherwise we can only do: nothing, polling, polling+irq
>> but not irq alone.
>> 
>> The jz4780 hdmi subsystem (drm/bridge/dw-hdmi.c) uses
>> 
>> 	connector->polled = DRM_CONNECTOR_POLL_HPD;
>> 
>> but shouldn't this enable polling? Note that there seems to be
>> no (direct) call to drm_kms_helper_poll_init().
>> 
>> If we set dev->mode_config.poll_enabled = true in
>> drm_helper_hpd_irq_event() things start to work.
>> 
>> Please can you clarify what would be best practise here to
>> get HPD event handling working.
>> 

Remove that - this stuff is for hardware without interrupts, where 
everything has to be polled.

>> The other issue is in dw-hdmi.c:
>> 
>> We found out that ingenic_drm_encoder_atomic_check() fails because
>> 
>> info->num_bus_formats == 0
>> 
>> and not 1. This blocks further initialization.
>> 
>> The reason seems to be that dw_hdmi_bridge_attach() does not call
>> drm_display_info_set_bus_formats() with a proper format like
>> other drivers (e.g. drm/bridge/ti-tfp410.c) are doing.
>> 
>> We have patched to set a single bus format MEDIA_BUS_FMT_RGB888_1X24
>> and then DRM setup seems to work (although we still have no valid
>> HDMI signal but that is likely something else).
>> 
>> Please can you explain how setting the bus format should be fixed
>> in dw-hdmi.c.
>> 

I'm not sure, but that information may come from EDID data. Are you 
able to obtain video modes from the connected monitor?

-Paul

>> If these questions should be forwarded to other specialists, please
>> do so.
> 
> It should be sent to the DRI mailing list, you missed the most 
> important one.
> 
> -Paul
> 
>> 
>> BR and thanks,
>> Nikolaus Schaller