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

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On 9 December 2016 at 19:09, Rob Herring <robh@xxxxxxxxxx> wrote:
> On Fri, Dec 02, 2016 at 01:06:47AM -0800, Matt Ranostay wrote:
>> On Fri, Dec 2, 2016 at 12:28 AM, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>> > On 2 December 2016 at 08:22, Matt Ranostay <matt@ranostay.consulting> wrote:
>> >>
>> >>
>> >>> On Dec 1, 2016, at 23:13, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
>> >>>
>> >>>> On 2 December 2016 at 07:17, Matt Ranostay <matt@ranostay.consulting> wrote:
>> >>>> Add optional device-post-power-on parameters to disable post_power_on
>> >>>> function from being called since this breaks some device.
>> >>>>
>> >>>> Cc: Tony Lindgren <tony@xxxxxxxxxxx>
>> >>>> Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
>> >>>> Signed-off-by: Matt Ranostay <matt@ranostay.consulting>
>> >>>> ---
>> >>>> Documentation/devicetree/bindings/mmc/mmc-pwrseq-simple.txt | 2 ++
>> >>>> drivers/mmc/core/pwrseq_simple.c                            | 7 +++++++
>> >>>> 2 files changed, 9 insertions(+)
>> >>>>
>> >>>> diff --git a/Documentation/devicetree/bindings/mmc/mmc-pwrseq-simple.txt b/Documentation/devicetree/bindings/mmc/mmc-pwrseq-simple.txt
>> >>>> index bea306d772d1..09fa153f743e 100644
>> >>>> --- a/Documentation/devicetree/bindings/mmc/mmc-pwrseq-simple.txt
>> >>>> +++ b/Documentation/devicetree/bindings/mmc/mmc-pwrseq-simple.txt
>> >>>> @@ -24,6 +24,8 @@ Optional properties:
>> >>>>        de-asserting the reset-gpios (if any)
>> >>>> - invert-off-state: Invert the power down state for the reset-gpios (if any)
>> >>>>        and pwrdn-gpios (if any)
>> >>>> +- disable-post-power-on : Avoid post_power_on function from being called since
>> >>>> +       this breaks some devices
>> >>>
>> >>> This is a bit weird. I would like to avoid this, if possible.
>> >>>
>> >>> Perhaps if you simply describe the sequence in detail for your device
>> >>> we can figure out the best option together.
>> >>
>> >> Yeah I know it is a bit weird but we need to keep that reset pin high for at least some time after pre power on.   So any case it would be another property
>> >
>> > This went offlist, please resend.
>> >
>> > Moreover, please try to describe the sequence you need in detail
>> > according to your HW spec.
>> >
>>
>> Yeah oops....
>>
>> So basically we need to drive the reset and powerdown lines high with
>> a 300 milliseconds delay between both...
>> can't have the reset line low with post power on (pretty sure but
>> would need a delay anyway), and we need both reset + powerdown line
>> set low on powerdown.
>>
>> So the power down sequence would need to be reversed for this
>> application in pwrseq-simple.
>
> This sounds like you need a device specific sequence to me. Otherwise,
> write a language to describe any power control waveforms rather than
> trying to bolt on more and more properties. (Don't really go write a
> language.)

Actually this isn't so device specific. The cw1200 wifi chip which is
being used with ux500 SoCs has a very similar sequence. Allow me to
check the details and get back.

Anyway, my point is that I think we can figure out a common sequence
to support these kind required sequences. That is to me preferred over
adding a new (two to support cw1200) device specific pwrseq driver.

Kind regards
Uffe
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