Re: [PATCH 3/3] clk: tegra: T114: add DFLL DVCO reset control

From: Prashant Gaikwad
Date: Tue Jun 11 2013 - 03:31:42 EST

On Friday 07 June 2013 10:36 PM, Paul Walmsley wrote:
Hi Stephen,

On Fri, 7 Jun 2013, Stephen Warren wrote:

On 06/07/2013 06:19 AM, Paul Walmsley wrote:
Add DFLL DVCO reset line control functions to the CAR IP block driver.

The DVCO present in the DFLL IP block has a separate reset line,
exposed via the CAR IP block. This reset line is asserted upon SoC
reset. Unless something (such as the DFLL driver) deasserts this
line, the DVCO will not oscillate, although reads and writes to the
DFLL IP block will complete.

Thanks to Aleksandr Frid <afrid@xxxxxxxxxx> for identifying this and
saving hours of debugging time.
diff --git a/drivers/clk/tegra/clk.h b/drivers/clk/tegra/clk.h
void tegra114_clock_tune_cpu_trimmers_high(void);
void tegra114_clock_tune_cpu_trimmers_low(void);
void tegra114_clock_tune_cpu_trimmers_init(void);
+void tegra114_clock_assert_dfll_dvco_reset(void);
+void tegra114_clock_deassert_dfll_dvco_reset(void);
Where/what is the code that will call these new APIs? If it's going to
be something in drivers/clk, that seems fine.
That's correct - they'll be used by the DFLL clocksource code, which will
live in drivers/clk/tegra. You've seen the patches already ;-)

Why not implement these APIs in DFLL clock driver itself and pass RST address register to driver?

The reset assert/de-assert functions at least might be worth exposing
using the new generic module reset API. I believe Prashant Gaikwad is
working on converting the Tegra clock driver to be a module reset
provider, hence removing the existing custom
tegra_periph_reset_{de,}assert() APIs.
OK, will take a look to see if this can be done without getting in the way
of Prashant's work. I'd naïvely assume that it might be best to convert
these as part of his series - that way we won't duplicate effort.

Prashant, what stage are you at in the conversion? If you're close to
completion, maybe we can just add this functionality in with your patches?

You can continue with this patch. I do not see any need to add this reset control to generic reset module.

- Paul

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