moving Tegra30 to the common clock framework

[skannan at codeaurora.org]

> On 05/08/2012 10:15 AM, Turquette, Mike wrote:
>> On Mon, May 7, 2012 at 10:07 PM, zhoujie wu<zhoujiewu at gmail.com>  wrote:
>>> Hi Mike,
>>> Could you please explain more details about how to implement a
>>> re-parenting operation as part of it's .set_rate implementation?
>>
>> Sure.
>>
>>> As far as I know, we can not call clk_set_parent in .set_rate function
>>> directly, since clk_set_rate and clk_set_parent are using the same
>>> prepare_lock.
>>
>> That is correct.
>>
>>> Any other interface can be used to implement it?
>>
>> You have two options available to you.
>>
>> 1) __clk_reparent can be used from your .set_rate callback today to
>> reflect changes made to the tree topology.  OMAP uses this in our PLL
>> .set_rate implementation: depending on the re-lock frequency the PLL
>> may switch parents dynamically.  __clk_reparent does the
>> framework-level cleanup needed for this (that function is also used
>> when populating the clock tree with new clock nodes).
>>
>> 2) __clk_set_parent could be made non-static if you needed this (I've
>> been meaning to talk to Saravana about this since I think MSM needs
>> something like this).
>
> Thanks!
>
> I don't think I need (2). But I don't think I can use (1) as is either.
> I can use (1) with some additional code in my set rate op.
>
> While set rate is in progress, both the parents might need to stay
> enabled for a short duration. So, in my internal set rate, I need to
> check if my clock is prepared/enabled and call prepare/enable on the
> "old parent", call __clk_reparent (which will reduce the ref count for
> the old parents and increase it for the new parents), finish the
> reparent in HW and then unprepare/disable the old parent if I have
> prepared/enabled them earlier.
>
> It might be beneficial to provide something like a
> __clk_reparent_start(new_parent, *scratch_pointer) and
> __clk_reparent_finish(*scratch_pointer) if it will be useful for more
> than just MSM. Based on this email, I would guess that Tegra would want
> something similar too.

Thinking more about this, I think this is how any clk op that might change
the parent should operate. I will try to write up an RFC patch for this
and send it out soon. I'm in a hurry, so will explain more in the RFC
patch or in a later email.

Thanks,
Saravana

--
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.