Re: [PATCH v7 1/6] base: power: runtime: Export pm_runtime_get/put_suppliers

[Robin Murphy]

On 13/02/18 07:44, Tomasz Figa wrote:
> Hi Vivek,
>
> On Wed, Feb 7, 2018 at 7:31 PM, Vivek Gautam
> <vivek.gautam@xxxxxxxxxxxxxx> 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.