Re: [PATCH] clk: qcom: gdsc: Remove direct runtime PM calls

Bjorn Andersson
2022-11-02T02:49:36Z

On Tue, Nov 01, 2022 at 04:34:21PM -0700, Stephen Boyd wrote:
> We shouldn't be calling runtime PM APIs from within the genpd
> enable/disable path for a couple reasons.
[..][
> Upon closer inspection, calling runtime PM APIs like this in the GDSC
> driver doesn't make sense. It was intended to make sure the GDSC for the
> clock controller providing other GDSCs was enabled, specifically the
> MMCX GDSC for the display clk controller on SM8250 (sm8250-dispcc), so
> that GDSC register accesses succeeded. That will already happen because
> we make the 'dev->pm_domain' a parent domain of each GDSC we register in
> gdsc_register() via pm_genpd_add_subdomain(). When any of these GDSCs
> are accessed, we'll enable the parent domain (in this specific case
> MMCX).
>

It's correct that adding the GDSCs as subdomains for the device's
parent-domain will ensure that enabling a GDSC will propagate up and
turn on the (typically) rpmhpd resource.

But the purpose for the explicit calls was to ensure that the clock
controller itself is accessible. It's been a while since I looked at
this, but iirc letting MMCX to turn off would cause the register access
during dispcc probing to fail - similar to how
clk_pm_runtime_get()/put() ensures the clock registers are accessible.

Perhaps I misunderstood something in the process, or lost track of the
actual issues?

Regards,
Bjorn