Re: [PATCH 1/2] clk: qcom: gcc-msm8996: Fix parent for CLKREF clocks

Bjorn Andersson
2019-12-26T22:42:13Z

On Mon 23 Dec 18:20 PST 2019, Stephen Boyd wrote:

> Quoting Bjorn Andersson (2019-12-19 18:34:27)
> > On Wed 18 Dec 22:37 PST 2019, Stephen Boyd wrote:
> >
> > > Quoting Bjorn Andersson (2019-12-07 12:36:02)
> > > > The CLKREF clocks are all fed by the clock signal on the CXO2 pad on the
> > > > SoC. Update the definition of these clocks to allow this to be wired up
> > > > to the appropriate clock source.
> > > >
> > > > Retain "xo" as the global named parent to make the change a nop in the
> > > > event that DT doesn't carry the necessary clocks definition.
> > >
> > > Something seems wrong still.
> > >
> > > I wonder if we need to add the XO "active only" clk to the rpm clk
> > > driver(s) and mark it as CLK_IS_CRITICAL. In theory that is really the
> > > truth for most of the SoCs out there because it's the only crystal that
> > > needs to be on all the time when the CPU is active. The "normal" XO clk
> > > will then be on all the time unless deep idle is entered and nobody has
> > > turned that on via some clk_prepare() call. That's because we root all
> > > other clks through the "normal" XO clk that will be on in deep
> > > idle/suspend if someone needs it to be.
> > >
> >
> > The patch doesn't attempt to address the fact that our representation of
> > XO is incomplete, only the fact that CXO2 isn't properly described.
> >
> > Looking at the clock distribution, we do have RPM_SMD_BB_CLK1_A which
> > presumably is the clock you're referring to here - i.e. the clock
> > resource connected to CXO.
>
> I don't mean the buffer clks, but the XO resource specifically. It's the
> representation to the RPM that deep sleep/deep idle should or shouldn't
> turn off XO and achieve "XO shutdown". Basically it can never be off
> when the CPU is active because then the CPU itself wouldn't be clocked,
> but when the CPU isn't active we may want to turn it off if nothing is
> using it during sleep to clock some sort of wakeup logic or device that
> is active when the CPU is idle.
>

I see. So we're missing the representation of the "raw" CXO in
clk-smd-rpm.c, and I'm lacking some understanding of how these pieces
should be tied together for us to realize the "XO shutdown"...

> >
> > > Did the downstream code explicitly enable this ln_bb_clk in the phy
> > > drivers? I think it may have?
> > >
> >
> > Yes, afaict all downstream drivers consuming a CLKREF also consumes
> > LN_BB and ensures that this is enabled. So we've been relying on UFS to
> > either not have probed yet or that UFS probed successfully for PCIe and
> > USB to be functional.
> >
> > So either we need this patch to ensure that the requests propagates
> > down, or I need to patch up the PHY drivers to ensure that they also
> > vote for the PMIC clock - and I do prefer this patch.
>
> Cool. Yeah seems better to just indicate that the reference clks are
> clocked by something else and fix that problem now.
>

Let me know if I shouldn't interpret this sentence as "let's merge this
for now".

Regards,
Bjorn