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SubjectRe: [PATCH v7 1/6] base: power: runtime: Export pm_runtime_get/put_suppliers
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On 13/02/18 07:44, Tomasz Figa wrote:
> Hi Vivek,
>
> On Wed, Feb 7, 2018 at 7:31 PM, Vivek Gautam
> <vivek.gautam@codeaurora.org> wrote:
>> The device link allows the pm framework to tie the supplier and
>> consumer. So, whenever the consumer is powered-on the supplier
>> is powered-on first.
>>
>> There are however cases in which the consumer wants to power-on
>> the supplier, but not itself.
>> E.g., A Graphics or multimedia driver wants to power-on the SMMU
>> to unmap a buffer and finish the TLB operations without powering
>> on itself.
>
> This sounds strange to me. If the SMMU is powered down, wouldn't the
> TLB lose its contents as well (and so no flushing needed)?

Depends on implementation details - if runtime PM is actually
implemented via external clock gating (in the absence of fine-grained
power domains), then "suspended" TLBs might both retain state and not
receive invalidation requests, which is really the worst case.

> Other than that, what kind of hardware operations would be needed
> besides just updating the page tables from the CPU?

Domain attach/detach also require updating SMMU hardware state (and
possibly TLB maintenance), but don't logically require the master device
itself to be active at the time.

Robin.

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