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

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Date:	Thu, 05 Sep 2013 01:03:59 +0300
From:	Mikko Perttunen <mikko.perttunen@...si.fi>
To:	Stephen Warren <swarren@...dotorg.org>
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 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.
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