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

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Message-ID: <20140721211630.GA12076@mithrandir>
Date:	Mon, 21 Jul 2014 23:16:32 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Alexandre Courbot <acourbot@...dia.com>,
	Terje Bergstrom <tbergstrom@...dia.com>,
	Mark Brown <broonie@...nel.org>,
	"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 Mon, Jul 21, 2014 at 09:35:27AM -0600, Stephen Warren wrote:
> On 07/02/2014 09:10 PM, Alexandre Courbot wrote:
> > On 07/03/2014 12:55 AM, Stephen Warren wrote:
> >> On 07/02/2014 06:19 AM, Alexandre Courbot wrote:
> >>> DSI support has been fixed to support continuous clock behavior that the
> >>> panel used on SHIELD requires, so finally add its device tree node since
> >>> it is functional.
> >>
> >>> diff --git a/arch/arm/boot/dts/tegra114-roth.dts
> >>> b/arch/arm/boot/dts/tegra114-roth.dts
> >>
> >>> +    host1x@...00000 {
> >>> +        dsi@...00000 {
> >>
> >> That node looks fine, but I wonder why we need to mark a bunch of
> >> regulators as always-on? shouldn't the references to vdd-supply and
> >> power-supply from this node be enough? If not, perhaps the tree
> >> structure of the regulators isn't correct, or the DSI or panel bindings
> >> don't allow enough regulators to be referenced?
> > 
> > regulator-always-on is indeed not needed for vdd_lcd. I actually had a
> > patch in my tree removing this line that I forgot to squash. Will post a
> > v2 for this patch that fixes this, thanks.
> > 
> > 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.

Thierry

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