linux-kernel - Re: [PATCH v7 06/20] clk: tegra: Support for OSC context save and restore

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Date:   Wed, 31 Jul 2019 14:04:51 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>, <thierry.reding@...il.com>,
        <jonathanh@...dia.com>, <tglx@...utronix.de>,
        <jason@...edaemon.net>, <marc.zyngier@....com>,
        <linus.walleij@...aro.org>, <stefan@...er.ch>,
        <mark.rutland@....com>
CC:     <pdeschrijver@...dia.com>, <pgaikwad@...dia.com>,
        <sboyd@...nel.org>, <linux-clk@...r.kernel.org>,
        <linux-gpio@...r.kernel.org>, <jckuo@...dia.com>,
        <josephl@...dia.com>, <talho@...dia.com>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <mperttunen@...dia.com>, <spatra@...dia.com>, <robh+dt@...nel.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH v7 06/20] clk: tegra: Support for OSC context save and
 restore


On 7/31/19 4:11 AM, Dmitry Osipenko wrote:
> 31.07.2019 3:20, Sowjanya Komatineni пишет:
>> This patch adds support for saving OSC clock frequency and the
>> drive-strength during OSC clock init and creates an API to restore
>> OSC control register value from the saved context.
>>
>> This API is invoked by Tegra210 clock driver during system resume
>> to restore the  OSC clock settings.
>>
>> Acked-by: Thierry Reding <treding@...dia.com>
>> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
>> ---
>>   drivers/clk/tegra/clk-tegra-fixed.c | 15 +++++++++++++++
>>   drivers/clk/tegra/clk.h             |  1 +
>>   2 files changed, 16 insertions(+)
>>
>> diff --git a/drivers/clk/tegra/clk-tegra-fixed.c b/drivers/clk/tegra/clk-tegra-fixed.c
>> index 8d91b2b191cf..7c6c8abfcde6 100644
>> --- a/drivers/clk/tegra/clk-tegra-fixed.c
>> +++ b/drivers/clk/tegra/clk-tegra-fixed.c
>> @@ -17,6 +17,10 @@
>>   #define OSC_CTRL			0x50
>>   #define OSC_CTRL_OSC_FREQ_SHIFT		28
>>   #define OSC_CTRL_PLL_REF_DIV_SHIFT	26
>> +#define OSC_CTRL_MASK			(0x3f2 |	\
>> +					(0xf << OSC_CTRL_OSC_FREQ_SHIFT))
>> +
>> +static u32 osc_ctrl_ctx;
>>   
>>   int __init tegra_osc_clk_init(void __iomem *clk_base, struct tegra_clk *clks,
>>   			      unsigned long *input_freqs, unsigned int num,
>> @@ -29,6 +33,7 @@ int __init tegra_osc_clk_init(void __iomem *clk_base, struct tegra_clk *clks,
>>   	unsigned osc_idx;
>>   
>>   	val = readl_relaxed(clk_base + OSC_CTRL);
>> +	osc_ctrl_ctx = val & OSC_CTRL_MASK;
>>   	osc_idx = val >> OSC_CTRL_OSC_FREQ_SHIFT;
>>   
>>   	if (osc_idx < num)
>> @@ -96,3 +101,13 @@ void __init tegra_fixed_clk_init(struct tegra_clk *tegra_clks)
>>   		*dt_clk = clk;
>>   	}
>>   }
>> +
>> +void tegra_clk_osc_resume(void __iomem *clk_base)
>> +{
>> +	u32 val;
>> +
>> +	val = readl_relaxed(clk_base + OSC_CTRL) & ~OSC_CTRL_MASK;
>> +	val |= osc_ctrl_ctx;
>> +	writel_relaxed(val, clk_base + OSC_CTRL);
> Why a full raw u32 OSC_CTRL value couldn't be simply saved and restored?

Storing and restoring only required fields to avoid accidental 
misconfiguration.

OSC_CTRL register has other bits (PLL_REF_DIV) which are configured by 
BR depending on OSC_FREQ and also setting PLL_REF_DIV while PLLS are in 
use is not safe.

>> +	fence_udelay(2, clk_base);
>> +}
>> diff --git a/drivers/clk/tegra/clk.h b/drivers/clk/tegra/clk.h
>> index f1ef6ae8c979..abba6d8a04cd 100644
>> --- a/drivers/clk/tegra/clk.h
>> +++ b/drivers/clk/tegra/clk.h
>> @@ -842,6 +842,7 @@ u16 tegra_pll_get_fixed_mdiv(struct clk_hw *hw, unsigned long input_rate);
>>   int tegra_pll_p_div_to_hw(struct tegra_clk_pll *pll, u8 p_div);
>>   int div_frac_get(unsigned long rate, unsigned parent_rate, u8 width,
>>   		 u8 frac_width, u8 flags);
>> +void tegra_clk_osc_resume(void __iomem *clk_base);
>>   
>>   
>>   /* Combined read fence with delay */
>>