linux-kernel - Re: [PATCH 1/2] omap: pm34xx: Enable IO / IO-CHAIN wakeups for PER

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Message-ID: <87wrvzxgok.fsf@deeprootsystems.com>
Date:	Thu, 22 Apr 2010 15:31:39 -0700
From:	Kevin Hilman <khilman@...prootsystems.com>
To:	Mike Chan <mike@...roid.com>
Cc:	tony@...mide.com, paul@...an.com, linux-omap@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH 1/2] omap: pm34xx: Enable IO / IO-CHAIN wakeups for PER

Mike Chan <mike@...roid.com> writes:

> On Wed, Apr 21, 2010 at 5:07 PM, Kevin Hilman
> <khilman@...prootsystems.com> wrote:
>> Mike Chan <mike@...roid.com> writes:
>>
>>> IO events can also come from GPIO modules, which reside in the PER domain.
>>> It is possible for the PER to enter RET while CORE is still in ON.
>>> If GPIO 2-6 are enabled for IO-pad wakeups, the PER domain will not
>>> wakeup in this case, unless we enable it.
>>>
>>> Signed-off-by: Mike Chan <mike@...roid.com>
>>
>> Hi Mike,
>>
>> I'm a little puzzled on this one.  My understanding is that the IO pad
>> is only armed when CORE is in RET or OFF.
>>
>
> The issue we are seeing is when the device is active but idle, if CORE
> is ON and PER is in RET and the omap is sitting in swfi. If the user
> presses a keypad button, IO pad doesn't wake us out of idle. Setting a
> wakeup if PER or CORE goes into RET solve this.
>
>> I need to dig a little more in the TRM on this one to clarify.
>>
>
> I was looking at 4.11.2.2 I/O Wake-Up Mechanism (pg 421)
>

Yeah, that's the right place.

After a little more digging and asking around, this looks like a good
fix, but there's a minor problem with the implementation:

In the section of the TRM you referenced the following sentence is
hiding:

  "Software must wait for the I/O daisy chain to complete before it
   transitions the PER domain to a nonfunctional state."

In the proposed patch, it's likely that PER could transition to
INACTIVE/RET/OFF before the IO wakeups are enabled.  For example, if
nothing in PER is active except UART3, then PER will transition to an
idle state right after omap_uart_prepare_idle(2), which is before
the IO wakeups are currently enabled.

To be perfectly safe, the IO wakeups should be enabled before PER is
allowed to transition.

Kevin





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