linux-kernel - Re: [PATCH 5/7] ARM: tegra: timer: Enable timer and rtc clocks

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Message-ID: <AANLkTi=pJw7oTUY2jmaSB=chds0fXFaA3+jrT=y8Jpzv@mail.gmail.com>
Date:	Tue, 22 Feb 2011 00:00:25 -0800
From:	Colin Cross <ccross@...roid.com>
To:	Olof Johansson <olof@...om.net>
Cc:	linux-tegra@...r.kernel.org, konkers@...roid.com,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	mike@...pulab.co.il, Russell King <linux@....linux.org.uk>
Subject: Re: [PATCH 5/7] ARM: tegra: timer: Enable timer and rtc clocks

On Mon, Feb 21, 2011 at 9:32 PM, Olof Johansson <olof@...om.net> wrote:
> Hi,
>
>
> On Mon, Feb 21, 2011 at 6:39 PM, Colin Cross <ccross@...roid.com> wrote:
>> Enable the timer and rtc clocks to prevent them being
>> turned off by the bootloader clock disabling code.
>>
>> Signed-off-by: Colin Cross <ccross@...roid.com>
>> ---
>>  arch/arm/mach-tegra/timer.c |   14 ++++++++++++--
>>  1 files changed, 12 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm/mach-tegra/timer.c b/arch/arm/mach-tegra/timer.c
>> index ffa6a68..31b4f56 100644
>> --- a/arch/arm/mach-tegra/timer.c
>> +++ b/arch/arm/mach-tegra/timer.c
>> @@ -18,6 +18,7 @@
>>  */
>>
>>  #include <linux/init.h>
>> +#include <linux/err.h>
>>  #include <linux/sched.h>
>>  #include <linux/time.h>
>>  #include <linux/interrupt.h>
>> @@ -193,9 +194,20 @@ static struct irqaction tegra_timer_irq = {
>>
>>  static void __init tegra_init_timer(void)
>>  {
>> +       struct clk *clk;
>>        unsigned long rate = clk_measure_input_freq();
>>        int ret;
>>
>> +       clk = clk_get_sys("timer", NULL);
>> +       BUG_ON(IS_ERR(clk));
>> +       clk_enable(clk);
>> +       clk_put(clk);
>> +
>> +       clk = clk_get_sys("rtc-tegra", NULL);
>> +       BUG_ON(IS_ERR(clk));
>> +       clk_enable(clk);
>> +       clk_put(clk);
>
> Why initialize the rtc clock here? Not all boards use it and instead
> use the rtc on the pmic. Seems wasteful to clock it unless the driver
> for it is probed and configured.

timekeeping_suspend uses read_persistent_clock and not the RTC driver
to track time in suspend.  The Tegra implementation of
read_persistent_clock reads from the internal RTC registers.  Its a 32
kHz clock, so it's power usage is negligible, and it is required on
all Tegra boards.
--
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