linux-kernel - Re: [PATCH 7/7] pinctrl: tegra: Add driver to configure voltage and power state of io pads

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Date:	Fri, 15 Apr 2016 19:29:56 +0530
From:	Laxman Dewangan <ldewangan@...dia.com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Stephen Warren <swarren@...dotorg.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Alexandre Courbot <gnurou@...il.com>,
	Rob Herring <robh+dt@...nel.org>,
	Mark Rutland <mark.rutland@....com>,
	Jon Hunter <jonathanh@...dia.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH 7/7] pinctrl: tegra: Add driver to configure voltage and
 power state of io pads


On Friday 15 April 2016 07:33 PM, Linus Walleij wrote:
> On Fri, Apr 15, 2016 at 1:47 PM, Laxman Dewangan <ldewangan@...dia.com> wrote:
>> On Friday 15 April 2016 04:45 PM, Linus Walleij wrote:
>>> On Fri, Apr 15, 2016 at 11:55 AM, Laxman Dewangan <ldewangan@...dia.com>
>>> wrote:
>>> But to be sure we would like to know what is actually happening,
>>> electronically speaking, when you set this up. Do you have any
>>> idea?
>>  From electronic point of view, the value of VIL, VIH, VOL, VOH (Input/output
>> voltage level for low and high state) are different when talking for 0 t
>> 1.8V and 0 to 3.3V.
> Yeah that I get. But since it is switched on a per-pin basis, and
> this is not about what voltage is actually supplied to the I/O cell,
> because that comes from the outside, it is a mystery why it is
> even needed.
>
> I understand that there is a bit selecting driving voltage level in
> the register range, what I don't understand is what that is
> doing in the I/O cell.
>
> The bit in the register must be routed to somehing in the I/O cell
> and I would like to know what. I take it that an ordinary CMOS
> totem-pole push-pull output is going to work the same with 1.8
> and 3.3V alike so it's obviously not enabling any extra transistors
> or anything.
>
>
I dont have answer for this now and I need to discuss with HW team to 
get this info.

I will be back here after discussion with HW team.