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

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Message-ID: <57113340.6090701@nvidia.com>
Date:	Fri, 15 Apr 2016 19:30:24 +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 18:49, Laxman Dewangan wrote:
> 
> On Friday 15 April 2016 11:14 PM, Jon Hunter wrote:
>> On 15/04/16 17:41, Laxman Dewangan wrote:
>>> On Friday 15 April 2016 09:15 PM, Jon Hunter wrote:
>>>> On 15/04/16 16:14, Laxman Dewangan wrote:
>>>>> 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?
>>> Which dt binding docs have these?
>>> I looked for nvidia,tegra210-pinmux.txt and not able to find csi_xxx.
>> For CSI you are right they are not included by the current DT binding
>> docs, however, the sdmmc1/3 pads are. So that makes things a bit more
>> messy as some are and some are not.
> 
> Yaah and so lets have the names in new dt files. Names may be same but
> define all possible names f groups in dt binding and need not to refer
> from other file which does not have all.

I still do not like that. In the case of sdmmc we now have two pinctrl
drivers to deal with for a single set of pins. That does not seem
correct IMO.

>>> Here I dont want to refer the individual pins as control should be as
>>> group.
>> I understand, however, at least for power-down control I don't see why
>> we cannot refer to the individual pins and once all are inactive then
>> the rail can be powered down.
>>
>> For switching the voltage it is a bit more complex, but may be we could
>> still look-up the IO rail based upon the pads the device uses.
>>
> 
> Yes, it can be done with ref count also for power down.

Exactly.

> But interfaces are complex. As a client, it is easy to say power down
> SDMMC1 IO interface rather than saying power down 10 pins (names) of
> that group.

Right and like I said, we could always look up the IO rail from the pins
associated once at probe time and then control it from there.

Cheers
Jon