linux-kernel - Re: [PATCH v7 05/16] clk: tegra: Add DFLL DVCO reset control for Tegra124

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Date:	Fri, 13 Feb 2015 12:39:03 +0200
From:	Mikko Perttunen <mikko.perttunen@...si.fi>
To:	Peter De Schrijver <pdeschrijver@...dia.com>
CC:	swarren@...dotorg.org, thierry.reding@...il.com, gnurou@...il.com,
	rjw@...ysocki.net, viresh.kumar@...aro.org, mturquette@...aro.org,
	pwalmsley@...dia.com, vinceh@...dia.com, pgaikwad@...dia.com,
	linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	tuomas.tynkkynen@....fi, Tuomas Tynkkynen <ttynkkynen@...dia.com>
Subject: Re: [PATCH v7 05/16] clk: tegra: Add DFLL DVCO reset control for
 Tegra124

On 02/12/2015 04:19 PM, Peter De Schrijver wrote:
> On Thu, Jan 08, 2015 at 03:22:08PM +0200, Mikko Perttunen wrote:
>> From: Paul Walmsley <pwalmsley@...dia.com>
>>
>> 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@...dia.com> for identifying this and
>> saving hours of debugging time.
>>
>
> Should this be done as a reset driver?

Probably through the already existing CAR reset driver. This reset 
doesn't fit well with the existing numbering scheme there, though. 
Perhaps a magic high-valued constant that represents it.

>
>> Signed-off-by: Paul Walmsley <pwalmsley@...dia.com>
>> [ttynkkynen: ported to tegra124 from tegra114]
>> Signed-off-by: Tuomas Tynkkynen <ttynkkynen@...dia.com>
>> Signed-off-by: Mikko Perttunen <mikko.perttunen@...si.fi>
>> ---
>>   drivers/clk/tegra/clk-tegra124.c | 47 ++++++++++++++++++++++++++++++++++++++++
>>   drivers/clk/tegra/clk.h          |  3 +++
>>   2 files changed, 50 insertions(+)
>>
>> diff --git a/drivers/clk/tegra/clk-tegra124.c b/drivers/clk/tegra/clk-tegra124.c
>> index f5f9bac..623b77f 100644
>> --- a/drivers/clk/tegra/clk-tegra124.c
>> +++ b/drivers/clk/tegra/clk-tegra124.c
>> @@ -31,6 +31,9 @@
>>   #define CLK_SOURCE_CSITE 0x1d4
>>   #define CLK_SOURCE_EMC 0x19c
>>
>> +#define RST_DFLL_DVCO			0x2f4
>> +#define DVFS_DFLL_RESET_SHIFT		0
>> +
>>   #define PLLC_BASE 0x80
>>   #define PLLC_OUT 0x84
>>   #define PLLC_MISC2 0x88
>> @@ -1399,6 +1402,50 @@ static void __init tegra124_clock_apply_init_table(void)
>>   	tegra_init_from_table(init_table, clks, TEGRA124_CLK_CLK_MAX);
>>   }
>>
>> +/**
>> + * tegra124_car_barrier - wait for pending writes to the CAR to complete
>> + *
>> + * Wait for any outstanding writes to the CAR MMIO space from this CPU
>> + * to complete before continuing execution.  No return value.
>> + */
>> +static void tegra124_car_barrier(void)
>> +{
>> +	readl_relaxed(clk_base + RST_DFLL_DVCO);
>> +}
>> +
>> +/**
>> + * tegra124_clock_assert_dfll_dvco_reset - assert the DFLL's DVCO reset
>> + *
>> + * Assert the reset line of the DFLL's DVCO.  No return value.
>> + */
>> +void tegra124_clock_assert_dfll_dvco_reset(void)
>> +{
>> +	u32 v;
>> +
>> +	v = readl_relaxed(clk_base + RST_DFLL_DVCO);
>> +	v |= (1 << DVFS_DFLL_RESET_SHIFT);
>> +	writel_relaxed(v, clk_base + RST_DFLL_DVCO);
>> +	tegra124_car_barrier();
>> +}
>> +EXPORT_SYMBOL(tegra124_clock_assert_dfll_dvco_reset);
>> +
>> +/**
>> + * tegra124_clock_deassert_dfll_dvco_reset - deassert the DFLL's DVCO reset
>> + *
>> + * Deassert the reset line of the DFLL's DVCO, allowing the DVCO to
>> + * operate.  No return value.
>> + */
>> +void tegra124_clock_deassert_dfll_dvco_reset(void)
>> +{
>> +	u32 v;
>> +
>> +	v = readl_relaxed(clk_base + RST_DFLL_DVCO);
>> +	v &= ~(1 << DVFS_DFLL_RESET_SHIFT);
>> +	writel_relaxed(v, clk_base + RST_DFLL_DVCO);
>> +	tegra124_car_barrier();
>> +}
>> +EXPORT_SYMBOL(tegra124_clock_deassert_dfll_dvco_reset);
>> +
>>   static void __init tegra124_clock_init(struct device_node *np)
>>   {
>>   	struct device_node *node;
>> diff --git a/drivers/clk/tegra/clk.h b/drivers/clk/tegra/clk.h
>> index 4e458aa..def0ea4 100644
>> --- a/drivers/clk/tegra/clk.h
>> +++ b/drivers/clk/tegra/clk.h
>> @@ -629,6 +629,9 @@ void tegra114_clock_tune_cpu_trimmers_init(void);
>>   void tegra114_clock_assert_dfll_dvco_reset(void);
>>   void tegra114_clock_deassert_dfll_dvco_reset(void);
>>
>> +void tegra124_clock_assert_dfll_dvco_reset(void);
>> +void tegra124_clock_deassert_dfll_dvco_reset(void);
>> +
>>   typedef void (*tegra_clk_apply_init_table_func)(void);
>>   extern tegra_clk_apply_init_table_func tegra_clk_apply_init_table;
>>
>> --
>> 2.2.1
>>

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