[PATCHv4 1/6] ARM: OMAP3 PM: correct enable/disable of daisy io chain

[rnayak@ti.com (Rajendra Nayak)]

On Tuesday 06 March 2012 09:23 AM, Rajendra Nayak wrote:
> Hi Paul,
>
> On Tuesday 06 March 2012 08:29 AM, Paul Walmsley wrote:
>>
>> cc'ing Nilesh, Rajendra

looks like you missed coping Nilesh. He's
copied in now.

>>
>> Hi
>>
>> On Fri, 2 Mar 2012, Tero Kristo wrote:
>>
>>> From: Mohan V<mohanv@ti.com>
>>>
>>> Currently the enabling and disabling of IO Daisy chain is not
>>> according to the TRM. The below steps are followed to enable/
>>> disable the IO chain according to the "Sec 3.5.7.2.2
>>> I/O Wake-Up Mechanism" in OMAP3630 Public TRM[1].
>>>
>>> Steps to enable IO chain:
>>> [a] Set PM_WKEN_WKUP.EN_IO bit
>>> [b] Set the PM_WKEN_WKUP.EN_IO_CHAIN bit
>>> [c] Poll for PM_WKST_WKUP.ST_IO_CHAIN.
>>> [d] When ST_IO_CHAIN bit set to 1, clear PM_WKEN_WKUP.EN_IO_CHAIN
>>
>> Looking at the above TRM section, it doesn't mention clearing
>> PM_WKEN_WKUP.EN_IO_CHAIN at all. This only seems to be mentioned (in a
>> rather unclear way) in the OMAP4430 TRM.
>>
>> Since Tero and Rajendra are reporting that this series works, I assume
>> that the conclusion is that this patch description just needs to be
>> fixed.
>> Could someone confirm that this is indeed the case -- that I/O wakeups
>> are
>> expected to work when EN_IO_CHAIN/WUCLK_CTRL is 0?
>
> Yes, thats my understanding too, again based on taking to people like
> Nilesh, because the documentation just doesn't mention this clearly.
> The 4430 TRM is a tad bit better like you said.
>
> I guess your confusion of IO wakeups working with EN_IO_CHAIN set to '0'
> is also probably coming from the fact that the bit itself is called
> *EN_IO_CHAIN* which is a completely *wrong* name for the bit, as
> compared to what it does.
> That bit is actually used to send a WUCLK pulse through the chain, so
> you set it to '1' and wait for it to propagate through the chain, then
> you set it to '0' and again wait for it to propagate through.
>
> The control to enable/disable is at 2 levels, a global switch which is
> 'EN_IO' in case of OMAP3 and the one at the individual pad level.
>
> You can also read this thread which has some more explanation based on
> my understanding of how this works
> http://www.spinics.net/lists/linux-serial/msg04480.html
>
> regards,
> Rajendra
>
>>
>> Is the I/O wakeup path from the pad to the PRCM wakeup line completely
>> asynchronous?
>>
>>
>> - Paul
>