Re: [PATCH] mmc: renesas_sdhi: don't lose RPM savings because of manual clk handling

[Masahiro Yamada <masahiroy@kernel.org>]

On Fri, May 15, 2020 at 6:26 PM Ulf Hansson <ulf.hansson@linaro.org> wrote:
>
> + Niklas, Geert, Yamada-san,
>
>
> On Wed, 13 May 2020 at 19:31, Wolfram Sang
> <wsa+renesas@sang-engineering.com> wrote:
> >
> > The SDHI driver en-/disabled clocks on its own during probe() and
> > remove(). This basically killed all potential RPM power savings. Now, we
> > just enable the clocks for a short time when we access registers in
> > probe(). We otherwise leave all handling to RPM. That means, we need to
> > shift the RPM enabling code in the TMIO core a bit up, so we can access
> > registers there, too.
>
> No, this doesn't sound entirely right to me.
>
> However, I do admit that we may need to move the pm_runtime
> initialization earlier (perhaps even out of tmio_mmc_core), but for
> slightly different reasons. Let me elaborate.
>
> For uniphier-sd, renesas_sdhi_sys_dmac and renesas_sdhi_internal_dmac
> - they all have assigned the ->clk_enable|disable() ops. Which means
> they have internal clock management (calling clk_prepare|enable()
> etc). For tmio_mmc, that's not the case.
>
> On top of this, the device may also have a potential PM domain
> attached. If that is the case, the PM domain may or may not have clock
> management implemented through genpd's ->start|stop() callbacks.
>
> So, in the end we are going to have to rely on clock enable/prepare
> reference counting, as we have to manage the clock(s) at both the
> driver and the PM domain level. Taking into account all various
> combinations (and that CONFIG_PM may not always be set). I have
> started to hack on some patches, but before I share them, let me ask a
> few questions.
>
> 1. tmio_mmc: - is that used solely with clock management through
> genpd? Or has no clock management at all?
> 2. uniphier-sd: Don't have runtime PM callbacks assigned. It looks
> like it doesn't care about runtime PM, but maybe it does through a PM
> domain? Can we skip to enable runtime PM for uniphier-sd, no?


Right, uniphier-sd does not care about runtime PM.
UniPhier SoCs do not have separate power domains.



-- 
Best Regards
Masahiro Yamada