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

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Message-ID: <20150212141944.GK20811@tbergstrom-lnx.Nvidia.com>
Date:	Thu, 12 Feb 2015 16:19:44 +0200
From:	Peter De Schrijver <pdeschrijver@...dia.com>
To:	Mikko Perttunen <mikko.perttunen@...si.fi>
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 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?

> 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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