linux-kernel - Re: [PATCH 4/4] ARM: tegra: roth: add display DT node

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Message-ID: <CAAVeFuKtVYNP5LFXGCEpkUtCCrK6AP+9WEVPDPs45RwAPvKKRg@mail.gmail.com>
Date:	Tue, 22 Jul 2014 13:39:51 +0900
From:	Alexandre Courbot <gnurou@...il.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	Thierry Reding <thierry.reding@...il.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Alexandre Courbot <acourbot@...dia.com>,
	Terje Bergstrom <tbergstrom@...dia.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4] ARM: tegra: roth: add display DT node

On Tue, Jul 22, 2014 at 7:51 AM, Mark Brown <broonie@...nel.org> wrote:
> On Mon, Jul 21, 2014 at 11:16:32PM +0200, Thierry Reding wrote:
>> On Mon, Jul 21, 2014 at 09:35:27AM -0600, Stephen Warren wrote:
>
>> > > vdd-2v8-display needs to remain always-on however. Here we may hit a
>> > > limitation of the simple-panel driver, where only one power supply can
>> > > be provided.
>
>> > Can't we fix the simple-panel driver to allow a list of regulators in
>> > the property?
>
>> I have no objection to allowing that. But I don't think there's a way to
>> do that with the current regulator API. You can use the bulk API, but
>> that requires separate properties, not multiple regulators in one
>> property.
>
>> Perhaps one idea to solve this would be to make the regulator API return
>> a regulator handle that in fact controls an array of regulators? Adding
>> Mark.
>
> I'm really not comfortable with that idea, it seems like most of the
> users would be abusing it - one of the biggest issues is always getting
> people to understand that their driver may be used in other systems with
> the supplies mapped differently.  If you were going to do something
> along those lines you'd need to do something that enumerated all the
> supply properties on the device.

I also don't think that would do it - for many displays the power-on
sequence is not as simple as "switch all the regulators on".

Maybe what we would want is to have panel-simple allow panels to
provide a "probe" callback so they can request and manage any extra
resource they need. This would of course imply that custom
enable/disable and suspend/resume callbacks. Then the driver might not
be "simple" anymore, but IMHO it would not be that bad.
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