[PATCH v3 6/7] mmc: sunxi: Add runtime_pm support

[maxime.ripard@bootlin.com (Maxime Ripard)]

On Fri, Jun 15, 2018 at 07:45:03AM -0700, Kevin Hilman wrote:
> > >
> > > With a working kernel, I see SATA and the wifi SDIO being probed.
> > >
> > > Happy to help testing stuff if you have any idea.
> >
> > In principle I would start with avoiding having the sunxi-mmc driver
> > to probe. Or bail out early in probe, whichever is the easiest for
> > you.
> >
> > The point is, if the sunxi-mmc driver doesn't even enable its clock,
> > it would be interesting to see if there are other that depends on it.
> >
> > One could also play with clk_disable_unused(), the
> > late_initcall_sync(), which can be turned off with the module
> > parameter "clk_ignore_unused".
> 
> I added clk_ignore_unused to the kernel command-line, and that didn't
> help, so it's not just an init-time clock that's causing the problem.
> 
> > Anyway, to hide/fix the problem for now, we could add a call to
> > pm_runtime_get_noresume() before the sunxi-driver calls
> > pm_runtime_enable().
> 
> I tried that and it makes the kernel finish booting, so that smells
> definitely like the MMC is disabling a clock when it goes idle that
> some other device (or CPU) depends on.

I quickly looked at the A10 and A20 clock driver and I have not seen
any obvious mishap.

If you have ftrace enabled, could you add the trace_clk_disable*
events (along with tp_printk since the kernel seems to break the
entire boot).

That will allow us to see which clock is disabled and shouldn't.

Thanks!
Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com
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