RE: [PATCH V2 1/3] iommu/arm-smmu: Add pm_runtime/sleep ops

["Sricharan" <sricharan-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

Hi Robin,

>-----Original Message-----
>From: linux-arm-kernel [mailto:linux-arm-kernel-bounces-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org] On Behalf Of Robin Murphy
>Sent: Wednesday, February 08, 2017 8:01 PM
>To: Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>; Sricharan <sricharan-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>
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>Subject: Re: [PATCH V2 1/3] iommu/arm-smmu: Add pm_runtime/sleep ops
>
>On 08/02/17 13:52, Mark Rutland wrote:
>> On Wed, Feb 08, 2017 at 07:15:37PM +0530, Sricharan wrote:
>>>> Clocks are not architectural, so it only makes sense to associate them
>>>> with an implementation-specific compatible string. There's also no
>>>
>>> ok, it for this the QCOM specific implementation binding is tried(going to).
>>>
>>>> guarantee that different microarchitectures have equivalent internal
>>>> clock domains - I'm not sure if "the SMMU's underlying bus access" is
>>>> meant to refer to accesses *by* the SMMU, i.e. page table walks,
>>>> accesses *through* the SMMU by upstream masters, or both
>>>
>>> In the above QCOM case, it is actually both. Its the same path for both the
>>> page table walker and upstream masters.
>
>Right, that's what I feared. As far as I can make out the current ARM
>implementations, transactions passing through will require at least
>TBUn_BCLK for the appropriate TBU, but would also need the page table
>walker clocked with CCLK to resolve TLB misses. But then the programming
>interface is also in the CCLK domain (not counting the incoming APB or
>AXI clock for the actual slave port itself). Thus this 'generic' clock
>binding already isn't compatible with MMU-40x/500.
>

Right, this implementation's clock bindings are not going to compatible with
MMU-500. There is also another soc which integrates MMU-500.  So
will have to add the clock bindings for MMU-500 as well separately.
Also in MMU-500 i saw that there is a possibility where the clock-domain
can be shared between the TCU logic, programming interface and PTW read
channel.  Does this mean that the TCU-clock has to be 'ON' for both register
access and PTW, similar to above ?. So for MMU-500 clock bindings there
can be a CFG_CLK (optional and not required in shared case), TBUn_CLK and
TCU_CLK

Regards,
 Sricharan

>>>> differences are rather significant. I'd also note that an MMU-500
>>>> configuration may have up to *33* clocks.
>>>>
>>>> Either way, the QCOM implementation deserves its own compatible if only
>>>> for the sake of the imp-def gaps in the architecture (e.g. FSR.SS
>>>> behaviour WRT to IRQs as touched upon in the other thread).
>>>>
>>>
>>> Ok, slightly unclear, so you mean then *clocks* are not good enough reason
>>> to have a new compatible ?
>>
>> I beleive Robin's point was even if the clocks didn't matter, there are
>> other reasons we should have the QCOM-specific compatible string.
>>
>> So we should have one regardless.
>
>Exactly.
>
>Robin.
>
>>
>> Thanks,
>> Mark.
>>
>
>
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