Re: [PATCH 1/6] omap: iommu: remove redundant clock usage

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On Sat, Nov 6, 2010 at 2:11 PM, Cousson, Benoit <b-cousson@xxxxxx> wrote:
> On 11/5/2010 9:19 PM, Ramirez Luna, Omar wrote:
>>
>> iommu driver is meant to provide control of mmu hardware blocks
>
> A dot is missing here, and a capital letter should follow.

Actually it is a comma, it is meant to be part of the same paragraph.

>
>> its current users (MMUs) are part of larger subsystems and do not
>> have a dedicated clock as the one they use is shared with the
>> entire subsystem, it doesn't make sense to enable/disable on each
>> register read/write operation as the driver using its interface
>> should also be handling the same clock.
>>
>> iommu should only enable/disable the clock on mmu request/free from
>> the driver wanting to use it.
>
> Mmm, I'm not necessarily convinced by that explanation.
> If in a next revision, we change the clock partitioning and provide a
> dedicated clock for the mmu, it will not work anymore.
> I don't thing you should assume anything about the current partitioning.

HW wise, only one clock feeds the mmu, iva2_ck is used to generate
three clocks but this inside the IVA2 module. I'm assuming omap4 dsp
is the same.

ISP also depends on cam_ick (among others), and mmu is inside ISP module afaik.

>From what I have checked on omap4 TRM it is the same, mmu doesn't have
a direct clock, it relies on the main ipu clock to function, but it is
my first glance to omap4 and I might be wrong.

> That being said, when you will change that code to switch to runtime PM, you
> will end up managing the module state in the ISR context.

Mainly this patch was sent on my laziness to add device enable/disable
calls on all the parts the code is using clk disable/enable, given
that they are not really needed.

Regards,

Omar
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