Re: CEC blocks idle on omap4

From: Tony Lindgren <tony@atomide.com>
To: Hans Verkuil <hverkuil@xs4all.nl>
Cc: linux-omap@vger.kernel.org,
	Tomi Valkeinen <tomi.valkeinen@ti.com>,
	Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
	dri-devel@lists.freedesktop.org, linux-media@vger.kernel.org
Subject: Re: CEC blocks idle on omap4
Date: Mon, 25 Mar 2019 09:33:59 -0700	[thread overview]
Message-ID: <20190325163359.GN19425@atomide.com> (raw)
In-Reply-To: <ce79cce0-bbd7-95e3-2035-c99be6c94cb4@xs4all.nl>

* Hans Verkuil <hverkuil@xs4all.nl> [190325 16:28]:
> On 3/25/19 5:21 PM, Tony Lindgren wrote:
> > * Hans Verkuil <hverkuil@xs4all.nl> [190325 16:12]:
> >> On 3/25/19 4:55 PM, Laurent Pinchart wrote:
> >>>> The reality is that HDMI CEC and HDMI video are really independent of
> >>>> one another. So I wonder if it isn't better to explain the downsides
> >>>> of enabling CEC for the omap4 in the CONFIG_OMAP4_DSS_HDMI_CEC
> >>>> description. And perhaps disable it by default?
> >>>
> >>> This should be controllable by userspace. From a product point of view,
> >>> it should be possible to put the system in a deep sleep state where CEC
> >>> isn't available, or in a low sleep state where CEC works as expected.
> >>>
> >>
> >> Userspace can always disable CEC. The hdmi_cec_adap_enable() callback in
> >> hdmi4_cec.c is called whenever the CEC adapter is enabled or disabled.
> > 
> > OK
> > 
> >> I'm not actually sure why hdmi4_cec_init() would block anything since it
> >> just registers the CEC device. It does not enable it until userspace
> >> explicitly enables it with e.g. 'cec-ctl --playback'.
> >>
> >> hdmi4_cec_init() does configure a CEC clock, but that can be moved to
> >> hdmi_cec_adap_enable() if necessary.
> > 
> > Hey I'm pretty sure that's the right fix then :)
> > 
> >> Note that I am not sure what is meant with 'SoC core retention idle',
> >> so perhaps I just misunderstand the problem.
> > 
> > If certain SoC clocks are busy, the SoC will not enter deeper
> > idle states. The hardware has autoidle type features on omaps.
> 
> Can you make a patch? It is very easy to test:

Sure. Hmm then we just clear HDMI_WP_CLK values then for disable
too I guess.

> To configure the CEC adapter: cec-ctl --playback
> To unconfigure the CEC adapter: cec-ctl --clear
> 
> As long as the CEC adapter is unconfigured you should be able to enter
> the deeper idle states. But not if it is configured.

OK will test tonight.

> And if you are moving code anyway, can you fix the typo in the comment?
> devider -> divider
> 
> That hurts my eyes...

Sure.

Thanks,

Tony
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