Subject: [PATCH 05/11] OMAPDSS: add clk_prepare and clk_unprepare

From: [email-masked] (Rajendra Nayak)
Date: Wed, 27 Jun 2012 10:49:24 +0530

On Wednesday 27 June 2012 09:49 AM, Tomi Valkeinen wrote:
> On Tue, 2012-06-26 at 17:47 -0700, Mike Turquette wrote:
>> On 20120625-16:14, Tomi Valkeinen wrote:
>>> A question about clk_prepare/unprepare, not directly related: let's say
>>> I have a driver for some HW block. The driver doesn't use clk functions,
>>> but uses runtime PM. The driver also sets pm_runtime_irq_safe().
>>>
>>> Now, the driver can call pm_runtime_get_sync() in an atomic context, and
>>> this would lead to the underlying framework (hwmod, omap_device, I don't
>>> know who =) enabling the func clock for that HW. But this would happen
>>> in atomic context, so the underlying framework can't use clk_prepare.
>>>
>>> How does the underlying framework handle that case? (sorry if that's a
>>> stupid question =).
>>>
>>
>> I think it's a good question!
>>
>> If we're going to call clk_prepare_enable from within a runtime pm
>> callback then I think we'll need to check if _irq_safe() is set and
>> conditionally call only clk_enable in such a case.
>>
>> I'm not a runtime pm expert, but if the driver owns the responsibility
>> of calling pm_runtime_irq_safe then the driver has the proper context
>> to know that it should call clk_prepare BEFORE calling
>> pm_runtime_get_sync.
>
> That's not quite what I meant. If it's the driver that does clk_enable,
> be it in runtime PM callback or not, it's driver's responsibility.
>
> But some clocks are not handled by the driver, but the hwmod/omap_device
> framework. Mainly I think this is for the functional and interface
> clocks. The driver has no visibility to those, they are implicitly
> enabled via pm_runtime_get.

yes, thats the tricky part on how would hwmod/omap_device know if the
driver would use runtime pm within atomic context or non-atomic context.
The driver does inform the runtime pm framework about this by calling a
pm_runtime_irq_safe(), which is then used to set the .irq_safe flag 
telling it to leave the interrupts disabled during callbacks.
This information however does not flow down to hwmod/omap_device in any
way. So the way its currently handled is to do an early prepare of all
hwmod controlled clocks.

I have copied Kevin in case he has any better ideas on how this should
be handled.

>   Tomi