drm/exynos: probe deferral for sub drivers

[Andrzej Hajda]

On 21.09.2016 00:07, Tobias Jakobi wrote:
> Hello,
>
> I'm currently facing the following problem.
>
> I want to use a devfreq device in one of the Exynos sub drivers, namely
> the G2D sub driver. My current approach is to use
> devfreq_get_devfreq_by_phandle() in g2d_probe(). But at the G2D probing
> time the devfreq subsystem isn't initialized yet, and I get EPROBE_DEFER
> back.
>
> Now I simply let g2d_probe() fail with EPROBE_DEFER in that case.
> Eventually devfreq is online and g2d_probe() runs successfully.
>
> So far, so good. However some debugging shows that g2d_subdrv_probe(),
> which does IOMMU setup and allocates the cmdlist, never happens in that
> case.
>
> I've looked at exynos_drm_load() which issues
> exynos_drm_device_subdrv_probe() at some point, which apparantly only
> probes those devices which are registered at that time. Hence, if the
> G2D probe hasn't happened until then, the Exynos DRM won't ever see it.
>
> That made me wonder how the driver makes sure that the sub drivers are
> all readily probed in that situation. I see that a component_bind_all()
> is issued prior to subdrv probing, but both the G2D and the IPP subdrv
> don't have bind/unbind calls. I guess subdrv != subdrv, eh?
>
> At present it appears that it's merely luck that the G2D is probed when
> sub drivers are probed?
>
> Anyway, probe deferral seems to work correctly with Exynos HDMI, so I
> was wondering if there is some way to also make it work with the G2D?

HDMI is componentized, G2D no, so it does not work with deferred probe.
The best solution at the moment is to componentize G2D, it should
not be difficult.

Regards
Andrzej

>
> Thanks in advance!
>
> With best wishes,
> Tobias
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