linux-kernel - Re: [PATCH 6/7] pinctrl: tegra: Add DT binding for io pads control

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Date:	Fri, 15 Apr 2016 16:45:40 +0100
From:	Jon Hunter <jonathanh@...dia.com>
To:	Laxman Dewangan <ldewangan@...dia.com>, <swarren@...dotorg.org>,
	<thierry.reding@...il.com>, <linus.walleij@...aro.org>,
	<gnurou@...il.com>, <robh+dt@...nel.org>, <mark.rutland@....com>
CC:	<linux-tegra@...r.kernel.org>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linux-gpio@...r.kernel.org>
Subject: Re: [PATCH 6/7] pinctrl: tegra: Add DT binding for io pads control


On 15/04/16 16:14, Laxman Dewangan wrote:
> On Friday 15 April 2016 08:44 PM, Jon Hunter wrote:
>> On 15/04/16 15:12, Laxman Dewangan wrote:
>>>
>>>
>>> All CSI pads are lined to single IO rail.
>> I agree with this and from the data-sheet I see the rail that powers the
>> CSI (and DSI) interfaces is called AVDD_DSI_CSI. But again, in the DT
>> document you are referring to csia, csib, csic, csid, csie, csif as
>> pins, but these don't appear to be physical pins, and this appears to be
>> more of a software means to control power to the various csi_x pins.
>>
>> It seems to me that each of the existing CSI_A_xxx pins/pads should be
>> mapped to or register with the appropriate power-down control and when
>> all pads are set to inactive this then triggers the power-down of all
>> the CSI_A_xxx pads.
>
> I used pins as this is the property from pincon generic so that I can
> use the generic implementation.
> 
> Here, I will not go to the pin level control as HW does not support pin
> level control.
> 
> I will say the unit should be interface level. Should we say
> IO_GROUP_CSIA, IO_GROUP_CSIB etc?

So we need to reflect the hardware in device-tree and although yes the
power-down for the CSI_x_xxx pads are all controlled together as a
single group, it does not feel right that we add a pseudo pin called
csix to represent these.

The CSI_x_xxx pads are already in device-tree and so why not add a
property to each of these pads which has the IO rail information for
power-down and voltage-select?

Cheers
Jon