Re: [PATCH 4/4] mmc: pwrseq-simple: add disable-post-power-on option

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On Wed, Jan 11, 2017 at 2:55 PM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
> On 9 January 2017 at 05:53, Matt Ranostay <matt@ranostay.consulting> wrote:
>> On Fri, Dec 30, 2016 at 12:05 AM, Linus Walleij
>> <linus.walleij@xxxxxxxxxx> wrote:
>>> On Mon, Dec 19, 2016 at 1:01 AM, Matt Ranostay <matt@ranostay.consulting> wrote:
>>>
>>>> * SD8787 has a "powerdown" line, and CW1200 has a "powerup" line.. I
>>>> know this is a simple logic inversion.
>>>
>>> If this is a GPIO line, the GPIO subsystem can flag a line for
>>> inverted logic. GPIO_ACTIVE_LOW from device tree for example.
>>
>> Slight ping on Ulf on this thread :).
>
> Thanks, sorry for the delay!
>
>>
>> I do understand the inverted logic flag but that doesn't help if there
>> are different logic states between various chipsets.
>
> For cw1200 (I looked at code from an old ST-Ericsson vendor tree), the
> sequence is as follows:
>
> 1) Enable clock/power to the card/chip.
> 2) Assert GPIO pin. I assume this also can be done before the
> clock/power is enabled.
> 3) Wait some time (~50ms).
> 4) De-assert GPIO pin.
> 5) Wait some time (~20ms)
> 6) Assert GPIO pin.
> 7) Wait some time (~32ms).
>
> At power off, the GPIO pin is de-asserted and of course also the
> clock/power is disabled. Just to make sure we have all the relevant
> logic.
>
> Looking at mmc pwrseq simple, perhaps we can extend this to deal with
> GPIOs that needs to be *toggled*, as this is not just reset GPIOs.
> Then we also need to deal with the delays in-between the toggling.

Wouldn't we need to have a per chip function for each device
supported? As well document gpios? I suspect we'd need an array of
gpios defined in device tree since different devices will likely have
various numbers of pins to toggle

- Matt

>
> Thoughts?
>
> Kind regards
> Uffe
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