Re: drm/exynos: probe deferral for sub drivers

From: Tobias Jakobi <tjakobi@math.uni-bielefeld.de>
To: Andrzej Hajda <a.hajda@samsung.com>,
	linux-samsung-soc <linux-samsung-soc@vger.kernel.org>,
	Maling list - DRI developers <dri-devel@lists.freedesktop.org>
Subject: Re: drm/exynos: probe deferral for sub drivers
Date: Thu, 22 Sep 2016 16:08:08 +0200	[thread overview]
Message-ID: <57E3E5C8.1090408@math.uni-bielefeld.de> (raw)
In-Reply-To: <444ad8a6-7ae8-d2f6-02b3-2aad99c759a9@samsung.com>

Hey Andrzej,

Andrzej Hajda wrote:
> 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.
I see! I try to look into this, but probably I'm going to ask for help
again. If that's OK with you? ;-)

With best wishes,
Tobias

> 
> Regards
> Andrzej
> 
>>
>> Thanks in advance!
>>
>> With best wishes,
>> Tobias
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> 

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