Hi Stephen,

On Sat, Jan 21, 2017 at 12:00 AM, Stephen Boyd [off-list ref] wrote:

On 01/17, Geert Uytterhoeven wrote:

quoted

This patch series adds support for the CLK_IS_CRITICAL flag to drivers
for module clocks on Renesas ARM SoCs.  For now, this is used to prevent
disabling of the ARM GIC module clock, which would lead to a system
lock-up when accessing the GIC's registers.

  1. The first patch migrates the Renesas CPG/MSSR driver from the
     never merged CLK_ENABLE_HAND_OFF flag to the CLK_IS_CRITICAL flag.
     Note that as the driver already handled critical clocks (i.e. it
     ignored them :-), this is not a prerequisite for linking the GIC to
     its module clock in DT.

  2. The second patch makes sure the CLK_IS_CRITICAL flag is set for the
     INTC-SYS clock on SoCs not (yet) using the Renesas CPG/MSSR driver.
     Note that this is a hard dependency for describing the INTC-SYS
     clock in DT on R-Mobile APE6 and R-Car Gen2.

I plan to queue these patches in my clk-renesas-for-v4.11 branch, if
you agree.

Would the runtime PM patches for ccf make things any better here?

It won't make much of a difference, as typically you'll want the GIC running
all the time anyway, also for wake-up sources.
We just have to make sure it's not disabled indefinitely.

As such it's different from a real critical clock that kills the system
immediately (e.g. some secret core clock): you can disable the GIC clock,
just make sure to enable it again (and have a means to re-enable it, without
relying on interrupts ;-)

The only difference with a real critical clock is that you

I still plan to support CLK_ENABLE_HAND_OFF somehow, but it's not
at the top of my priority list right now.

Good, we can convert back later, perhaps when the GIC driver is ready to
support PM for non-secondary GICs...

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds