[PATCH] ARM: dts: Add mask-tpm-reset to the device tree

[Doug Anderson]

Vikas,

On Wed, Jul 9, 2014 at 9:35 PM, Vikas Sajjan <vikas.sajjan at samsung.com> wrote:
> Doug,
>
> On Wed, Jul 9, 2014 at 8:52 PM, Doug Anderson <dianders at chromium.org> wrote:
>> Vikas,
>>
>> On Tue, Jul 8, 2014 at 9:20 AM, Tomasz Figa <t.figa at samsung.com> wrote:
>>> On 08.07.2014 17:27, Doug Anderson wrote:
>>>> Hi,
>>>>
>>>> On Tue, Jul 8, 2014 at 12:46 AM, Linus Walleij <linus.walleij at linaro.org> wrote:
>>>>> On Thu, Jun 26, 2014 at 11:15 AM, Vikas Sajjan <vikas.sajjan at samsung.com> wrote:
>>>>>
>>>>>> From: Doug Anderson <dianders at chromium.org>
>>>>>>
>>>>>> The mask-tpm-reset GPIO is used by the kernel to prevent the TPM from
>>>>>> being reset across sleep/wake.  If we don't set it to anything then
>>>>>> the TPM will be reset.  U-Boot will detect this as invalid
>>>>>> and will reset the system on resume time. This GPIO can always be low
>>>>>> and not hurt anything.  It will get pulled back high again during a
>>>>>> normal warm reset when it will default back to an input.
>>>>>>
>>>>>> To properly preserve the TPM state across suspend/resume and to make
>>>>>> the chrome U-Boot happy, properly set the GPIO to mask the
>>>>>> reset to the TPM.
>>>>>>
>>>>>> Signed-off-by: Doug Anderson <dianders at chromium.org>
>>>>>> Signed-off-by: Vikas Sajjan <vikas.sajjan at samsung.com>
>>>>> (...)
>>>>>> +       /* We need GPX0_6 to be low at sleep time; just keep it low always */
>>>>>> +       mask_tpm_reset_regulator: mask-tpm-reset-regulator {
>>>>>> +       compatible = "regulator-fixed";
>>>>>
>>>>> No matter how the discussion ends up, regulator-fixed is wrong.
>>>>
>>>> OK, fair enough.
>>>>
>>>>
>>>>> Either folding it into the TPM driver or using a separate reset driver
>>>>> is fine with me.
>>>>
>>>> OK, Vikas: do you want to code up the driver?
>>>>
>>>>
>>>>> So what about the generic delayed reset GPIO thing?
>>>>> http://marc.info/?l=linux-kernel&m=140309916607115&w=2
>>>>
>>>> That's a neat concept and could be useful in other cases, but I think
>>>> it's just as much of a hack as using a regulator.  This is not a reset
>>>> signal for the TPM.  This is a signal that will mask the CPU's reset
>>>> signal (using a special bit of board-specific logic).
>>>>
>>>>
>>>> Personally I think Tomasz's idea of using hogs (after his patches
>>>> allowing a default output level) is the cleanest, but I think Stephen
>>>> didn't like that.
>>>
>>> I don't see any benefits of using complex interfaces over simply
>>> initializing the pin to the right value once at boot-up or at
>>> suspend/resume. As far as I understand Doug's explanation of the
>>> problem, nothing else is expected from the OS with respect to this pin.
>>> Moreover it doesn't affect operation of any drivers.
>>>
>>> So I'm still for the simplest and effective solution, i.e. hogs.
>>
>> It looks as if Tomasz's patch has landed, so perhaps you could try to
>> code it up his way.  It should be very simple.  Please make sure to CC
>> Stephen Warren on the patch so that he is included in the discussion
>> (and of course include Tomasz, Linus W, etc).
>
> Can you point me to Tomasz's patchset on which I should rebase this patch on.

You can base it atop (0635c88 pinctrl: samsung: Allow pin value to be
initialized using pinfunc), which appears to be in linux-next.  That
gives you "samsung,pin-val".

You can use that together with a pinctrl "hog" to specify the state of
this pin for the board.

-Doug