[PATCH v7 17/21] OMAP2+: UART: Remove omap_uart_can_sleep and add pm_qos

[Kevin Hilman]

Govindraj <govindraj.ti at gmail.com> writes:

> Hi Kevin,
>
> On Wed, Nov 9, 2011 at 12:50 AM, Kevin Hilman <khilman at ti.com> wrote:
>> Rajendra Nayak <rnayak at ti.com> writes:
>>
>>> Hi Kevin,
>>>
>>> On Saturday 05 November 2011 04:12 AM, Kevin Hilman wrote:
>>>> However, as mentioned previously[1], due to a HW sleepdep between MPU
>>>> and CORE, this constraint isn't actually needed for CORE UARTs, so it's
>>>> a bit wasteful to go through all the constraint setting for no reason.
>>>
>>> I had a short chat with Govind on this and was trying to understand
>>> this better.
>>> Are you referring to the 'autodeps' for omap3 here, because they would
>>> prevent any clock domain from idling as long as MPU or IVA are active,
>>
>> No, I was thinking of HW sleepdeps.  However, I looked back at the
>> OMAP3430 TRM and see that MPU does not have a HW sleepdep on CORE like I
>> thought.
>>
>>> but not the other way round. Which means MPU can still idle, while CORE
>>> does not.
>>>
>>> My guess was, its probably the CORE domain idling itself thats causing
>>> the UART sluggishness, (and not MPU idling), due to higher latency,
>>> which is prevented with an active UART module in CORE, but not in PER.
>>
>> OK, that indeed makes sense.  Thanks for correcting me.
>>
>>> So Govind did a small experiment to prevent just CORE idling and let MPU
>>> idle alone and that did not show any sluggishness.
>>
>> OK, good.
>>
>>> Now, putting a pm-qos constraint for a UART in CORE still looks
>>> redundant because the latency requirement that UART has is in
>>> some way *indirectly* met (because the active UART in CORE prevents
>>> CORE transitions in idle).
>>> But don't you think the UART driver should express its
>>> latency constraints regardless, without thinking of any indirect ways
>>> in which the same requirements would have already been met?
>>
>> Yes, you're right.  The driver should not need to know which powerdomain
>> a given UART is in.  It's probably best (and most portable) to have UART
>> always express its requirements all the time.
>>
>> Thanks for digging into this,
>>
>
> I have fixed this and other uart_v7 comments and have re-based the
> patch series on top
> of 3.2-rc1 along with Tero's v9 irq chaining patches and tested the same.
> Available here [1].

Please repost your updated series.

> Can this patches series be added to a test branch for upstreaming or do you
> think there are still some outstanding comments that needs to be discussed?

The PRCM IRQ chaining series is not yet finalized.

Kevin