linux-kernel - Re: [PATCH v2 3/6] host1x: hdmi: Enable Vdd earlier for hotplug/DDC

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Message-ID: <5227B31A.3070404@wwwdotorg.org>
Date:	Wed, 04 Sep 2013 16:24:26 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Mikko Perttunen <mikko.perttunen@...si.fi>
CC:	Mikko Perttunen <mperttunen@...dia.com>, thierry.reding@...il.com,
	tbergstrom@...dia.com, dri-devel@...ts.freedesktop.org,
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/6] host1x: hdmi: Enable Vdd earlier for hotplug/DDC

On 09/04/2013 04:03 PM, Mikko Perttunen wrote:
> On 09/04/2013 09:44 PM, Stephen Warren wrote:
>> On 08/28/2013 09:48 AM, Mikko Perttunen wrote:
>>> The Vdd regulator used to be enabled only at tegra_output_hdmi_enable,
>>> which is called after a sink is detected. However, the HDMI hotplug pin
>>> works by returning the voltage supplied by the Vdd pin, so this meant
>>> that the hotplug pin was never asserted and the sink was not detected
>>> unless the Vdd regulator was set to be always on.
>>>
>>> This patch moves the enable to the tegra_hdmi_drm_init function to make
>>> sure the regulator will get enabled.
>>
>> The DT binding document isn't very clear on this topic (and should be
>> fixed): What is this regulator intended to control? If this regulator
>> solely controls the supply to the hotplug detection circuit, this change
>> makes sense. If the regulator mainly supplies something else (e.g. part
>> of the HDMI core on the Tegra chip), then perhaps this change isn't
>> correct. The correct approach might be to introduce another (optional)
>> regulator specifically for the hotplug circuit. Presumably both DT
>> properties vdd-supply and hotplug-supply could point at the same
>> regulator if that's the way the HW was wired up.
>> -- 
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>>
> 
> AFAICT, it controls the Vdd pin on the HDMI port, so it just affects the
> hotplug pin and the DDC I2C bus power.

Ah OK, then this code change makes sense. It'd be useful to put what you
just wrote into the binding doc.

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