io-domain voltages as regulators?

io-domain voltages as regulators?

[Heiko Stübner]

Hi Mark, Linus,

I'd like to clarify what the appropriate way to handle pin output voltages is. 
On the Rockchip SoCs the voltage for some groups of pins can be set between 
3.3V and 1.8V ... like the MMC/SD pins who need this to support UHS mode 
cards.

In [0] when talking about something different, Linus Walleij described a 
similar case as

"I think we need to have a discussion with Mark Brown on how to
handle this.
We have previously had the case of MMC/SD level-shifters, where
a certain setting gives a certain level of signals out, and another setting
gives another level. Like two discrete levels.
So we modeled that as a regulator provider inside the pin control
driver eventually, see sh-pfc/pfc-sh73a0.c"

As this sound like exactly the thing I'm trying to solve, is handling this via 
a regulator the correct general way?


Thanks
Heiko

[0] https://lkml.org/lkml/2014/5/28/147

Re: io-domain voltages as regulators?

[Mark Brown]

[-- Attachment #1: Type: text/plain, Size: 674 bytes --]

On Mon, Aug 04, 2014 at 12:18:40AM +0200, Heiko Stübner wrote:

> As this sound like exactly the thing I'm trying to solve, is handling this via 
> a regulator the correct general way?

My first thought is that it seems sensible if it's used as a regulated
supply in a context where just a plain regulator might be used like
MMC/SDIO type things.  If it's only setting logic levels for I/O pins
but isn't something that's being dynamically managed or really visible
to software (it's just a board design thing) then it might not be worth
it but if it might be controlled by changing an external regulator then
using the same API seems like it might be sensible.

[-- Attachment #2: Digital signature --]
[-- Type: application/pgp-signature, Size: 819 bytes --]

Re: io-domain voltages as regulators?

[Linus Walleij]

On Mon, Aug 4, 2014 at 12:18 AM, Heiko Stübner <heiko@sntech.de> wrote:

[Adding Ulf Hansson to this discussion...]

> Hi Mark, Linus,
>
> I'd like to clarify what the appropriate way to handle pin output voltages is.
> On the Rockchip SoCs the voltage for some groups of pins can be set between
> 3.3V and 1.8V ... like the MMC/SD pins who need this to support UHS mode
> cards.

This is called "vqmmc" in the mmc/sd subsystem.

grep for mmc_set_signal_voltage() in drivers/mmc/core/*

In drivers/mmc/core/core.c, you find:

 mmc->supply.vqmmc = devm_regulator_get_optional(dev, "vqmmc");

Which gets the regulator to set the signal voltage, if such
a regulator is specified for the host.

Very simple and straight-forward, and handled by the MMC core.

> In [0] when talking about something different, Linus Walleij described a
> similar case as
>
> "I think we need to have a discussion with Mark Brown on how to
> handle this.
> We have previously had the case of MMC/SD level-shifters, where
> a certain setting gives a certain level of signals out, and another setting
> gives another level. Like two discrete levels.
> So we modeled that as a regulator provider inside the pin control
> driver eventually, see sh-pfc/pfc-sh73a0.c"
>
> As this sound like exactly the thing I'm trying to solve, is handling this via
> a regulator the correct general way?

Ithinkso.

Yours,
Linus Walleij

Re: io-domain voltages as regulators?

[Ulf Hansson]

On 11 August 2014 09:44, Linus Walleij <linus.walleij@linaro.org> wrote:
> On Mon, Aug 4, 2014 at 12:18 AM, Heiko Stübner <heiko@sntech.de> wrote:
>
> [Adding Ulf Hansson to this discussion...]
>
>> Hi Mark, Linus,
>>
>> I'd like to clarify what the appropriate way to handle pin output voltages is.
>> On the Rockchip SoCs the voltage for some groups of pins can be set between
>> 3.3V and 1.8V ... like the MMC/SD pins who need this to support UHS mode
>> cards.
>
> This is called "vqmmc" in the mmc/sd subsystem.
>
> grep for mmc_set_signal_voltage() in drivers/mmc/core/*
>
> In drivers/mmc/core/core.c, you find:
>
>  mmc->supply.vqmmc = devm_regulator_get_optional(dev, "vqmmc");
>
> Which gets the regulator to set the signal voltage, if such
> a regulator is specified for the host.
>
> Very simple and straight-forward, and handled by the MMC core.
>
>> In [0] when talking about something different, Linus Walleij described a
>> similar case as
>>
>> "I think we need to have a discussion with Mark Brown on how to
>> handle this.
>> We have previously had the case of MMC/SD level-shifters, where
>> a certain setting gives a certain level of signals out, and another setting
>> gives another level. Like two discrete levels.
>> So we modeled that as a regulator provider inside the pin control
>> driver eventually, see sh-pfc/pfc-sh73a0.c"
>>
>> As this sound like exactly the thing I'm trying to solve, is handling this via
>> a regulator the correct general way?
>
> Ithinkso.

Just to confirm, I fully agree with the above said.

You may also find a good example in the mmci host driver for how to
make use of the vqmmc regulator.

Kind regards
Uffe

Re: io-domain voltages as regulators?

[Doug Anderson]

Hi,

On Mon, Aug 11, 2014 at 5:46 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> On 11 August 2014 09:44, Linus Walleij <linus.walleij@linaro.org> wrote:
>> On Mon, Aug 4, 2014 at 12:18 AM, Heiko Stübner <heiko@sntech.de> wrote:
>>
>> [Adding Ulf Hansson to this discussion...]
>>
>>> Hi Mark, Linus,
>>>
>>> I'd like to clarify what the appropriate way to handle pin output voltages is.
>>> On the Rockchip SoCs the voltage for some groups of pins can be set between
>>> 3.3V and 1.8V ... like the MMC/SD pins who need this to support UHS mode
>>> cards.
>>
>> This is called "vqmmc" in the mmc/sd subsystem.
>>
>> grep for mmc_set_signal_voltage() in drivers/mmc/core/*
>>
>> In drivers/mmc/core/core.c, you find:
>>
>>  mmc->supply.vqmmc = devm_regulator_get_optional(dev, "vqmmc");
>>
>> Which gets the regulator to set the signal voltage, if such
>> a regulator is specified for the host.
>>
>> Very simple and straight-forward, and handled by the MMC core.
>>
>>> In [0] when talking about something different, Linus Walleij described a
>>> similar case as
>>>
>>> "I think we need to have a discussion with Mark Brown on how to
>>> handle this.
>>> We have previously had the case of MMC/SD level-shifters, where
>>> a certain setting gives a certain level of signals out, and another setting
>>> gives another level. Like two discrete levels.
>>> So we modeled that as a regulator provider inside the pin control
>>> driver eventually, see sh-pfc/pfc-sh73a0.c"
>>>
>>> As this sound like exactly the thing I'm trying to solve, is handling this via
>>> a regulator the correct general way?
>>
>> Ithinkso.
>
> Just to confirm, I fully agree with the above said.
>
> You may also find a good example in the mmci host driver for how to
> make use of the vqmmc regulator.

Yuvaraj also submitted patches for dw_mmc:

4401241 New          [1/3] mmc: dw_mmc: use mmc_regulator_get_supply
to handle regulators
4401261 New          [2/3] mmc: dw_mmc: Dont cut off vqmmc and vmmc
4401281 New          [3/3] mmc: dw_mmc: Support voltage changes

He seems to have dropped these patches on the floor and I had review
feedback on them, but I think they're in the right direction.

Re: io-domain voltages as regulators?

[Yuvaraj Cd]

On Tue, Aug 12, 2014 at 8:43 PM, Doug Anderson <dianders@chromium.org> wrote:
> Hi,
>
> On Mon, Aug 11, 2014 at 5:46 AM, Ulf Hansson <ulf.hansson@linaro.org> wrote:
>> On 11 August 2014 09:44, Linus Walleij <linus.walleij@linaro.org> wrote:
>>> On Mon, Aug 4, 2014 at 12:18 AM, Heiko Stübner <heiko@sntech.de> wrote:
>>>
>>> [Adding Ulf Hansson to this discussion...]
>>>
>>>> Hi Mark, Linus,
>>>>
>>>> I'd like to clarify what the appropriate way to handle pin output voltages is.
>>>> On the Rockchip SoCs the voltage for some groups of pins can be set between
>>>> 3.3V and 1.8V ... like the MMC/SD pins who need this to support UHS mode
>>>> cards.
>>>
>>> This is called "vqmmc" in the mmc/sd subsystem.
>>>
>>> grep for mmc_set_signal_voltage() in drivers/mmc/core/*
>>>
>>> In drivers/mmc/core/core.c, you find:
>>>
>>>  mmc->supply.vqmmc = devm_regulator_get_optional(dev, "vqmmc");
>>>
>>> Which gets the regulator to set the signal voltage, if such
>>> a regulator is specified for the host.
>>>
>>> Very simple and straight-forward, and handled by the MMC core.
>>>
>>>> In [0] when talking about something different, Linus Walleij described a
>>>> similar case as
>>>>
>>>> "I think we need to have a discussion with Mark Brown on how to
>>>> handle this.
>>>> We have previously had the case of MMC/SD level-shifters, where
>>>> a certain setting gives a certain level of signals out, and another setting
>>>> gives another level. Like two discrete levels.
>>>> So we modeled that as a regulator provider inside the pin control
>>>> driver eventually, see sh-pfc/pfc-sh73a0.c"
>>>>
>>>> As this sound like exactly the thing I'm trying to solve, is handling this via
>>>> a regulator the correct general way?
>>>
>>> Ithinkso.
>>
>> Just to confirm, I fully agree with the above said.
>>
>> You may also find a good example in the mmci host driver for how to
>> make use of the vqmmc regulator.
>
> Yuvaraj also submitted patches for dw_mmc:
>
> 4401241 New          [1/3] mmc: dw_mmc: use mmc_regulator_get_supply
> to handle regulators
> 4401261 New          [2/3] mmc: dw_mmc: Dont cut off vqmmc and vmmc
> 4401281 New          [3/3] mmc: dw_mmc: Support voltage changes
>
> He seems to have dropped these patches on the floor and I had review
> feedback on them, but I think they're in the right direction.
I have not dropped these patches.I am trying out  [3/3] mmc: dw_mmc:
Support voltage changes without extra state machine as Seungwon Jeon
suggested.
I will post the next version soon.
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel