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

[Paul Cercueil]

Hi Nikolaus,


Le sam. 11 avril 2020 à 16:14, H. Nikolaus Schaller 
<hns@xxxxxxxxxxxxx> 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.
>
> 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.
>
>
> 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.
>
> 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