Re: [PATCH 1/4 v10] arm: use devicetree to get smp_twd clock

Rob Herring
2013-01-11T14:40:04Z

On 01/10/2013 05:34 PM, Russell King - ARM Linux wrote:
> Mark,
>
> Rafael just asked me to look at this patch, though I guess these comments
> should be directed to Rob who was the original patch author.
>
> On Fri, Jan 04, 2013 at 10:35:43AM -0600, Mark Langsdorf wrote:
>> diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c
>> index 49f335d..dad2d81 100644
>> --- a/arch/arm/kernel/smp_twd.c
>> +++ b/arch/arm/kernel/smp_twd.c
>> @@ -239,12 +239,15 @@ static irqreturn_t twd_handler(int irq, void *dev_id)
>> return IRQ_NONE;
>> }
>>
>> -static struct clk *twd_get_clock(void)
>> +static struct clk *twd_get_clock(struct device_node *np)
>> {
>> struct clk *clk;
>> int err;
>>
>> - clk = clk_get_sys("smp_twd", NULL);
>> + if (np)
>> + clk = of_clk_get(np, 0);
>> + else
>> + clk = clk_get_sys("smp_twd", NULL);
>> if (IS_ERR(clk)) {
>> pr_err("smp_twd: clock not found: %d\n", (int)PTR_ERR(clk));
>> return clk;
>> @@ -257,6 +260,7 @@ static struct clk *twd_get_clock(void)
>> return ERR_PTR(err);
>> }
>>
>> + twd_timer_rate = clk_get_rate(clk);
>
> Hmm, so this overrides the later clk_get_rate() in twd_timer_setup(), making
> the later one redundant. However...
>
>> return clk;
>> }
>>
>> @@ -285,7 +289,7 @@ static int __cpuinit twd_timer_setup(struct clock_event_device *clk)
>> * during the runtime of the system.
>> */
>> if (!common_setup_called) {
>> - twd_clk = twd_get_clock();
>> + twd_clk = twd_get_clock(NULL);
>>
>> /*
>> * We use IS_ERR_OR_NULL() here, because if the clock stubs
>> @@ -373,6 +377,8 @@ int __init twd_local_timer_register(struct twd_local_timer *tlt)
>> if (!twd_base)
>> return -ENOMEM;
>>
>> + twd_clk = twd_get_clock(NULL);
>> +
>> return twd_local_timer_common_register();
>
> Ok, so this sets up twd_clk, and also twd_timer_rate, but
> twd_local_timer_common_register() just ends up registering the set of
> function pointers with the local timer code. Some point later, the
> ->setup function is called, and that will happen with common_setup_called
> false. The result will be another call to twd_get_clock().
>
>> }
>>
>> @@ -405,6 +411,8 @@ void __init twd_local_timer_of_register(void)
>> goto out;
>> }
>>
>> + twd_clk = twd_get_clock(np);
>> +
>> err = twd_local_timer_common_register();
>
> And a similar thing happens here. Except... the twd_clk gets overwritten
> by the call to twd_get_clock(NULL) from twd_timer_setup().
>
> I wonder if it would be much better to move twd_get_clock() out of
> twd_timer_setup() entirely, moving it into twd_local_timer_common_register().
> twd_local_timer_common_register() would have to take the dev node.
> Also, leave the setting of twd_timer_rate in twd_timer_setup().
>
> An alternative strategy would be to move the initialization of the
> timer rate also into twd_local_timer_common_register(), detect the
> NULL or error clock, and run the calibration from there (I don't think
> we can move the calibration). If that's chosen, then "common_setup_called"
> should probably be renamed to "twd_calibration_done".
>
> What do you think?

Yes, things can be simplified a bit. How about this patch? I moved the clk
setup to twd_local_timer_common_register. Then we just rely on twd_timer_rate
being 0 when there is no clock and we need to do calibration. Then we can get
rid of common_setup_called altogether.

diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c
index dc9bb01..2201e2d 100644
--- a/arch/arm/kernel/smp_twd.c
+++ b/arch/arm/kernel/smp_twd.c
@@ -30,7 +30,6 @@ static void __iomem *twd_base;

static struct clk *twd_clk;
static unsigned long twd_timer_rate;
-static bool common_setup_called;
static DEFINE_PER_CPU(bool, percpu_setup_called);

static struct clock_event_device __percpu **twd_evt;
@@ -238,25 +237,28 @@ static irqreturn_t twd_handler(int irq, void *dev_id)
return IRQ_NONE;
}

-static struct clk *twd_get_clock(void)
+static void twd_get_clock(struct device_node *np)
{
- struct clk *clk;
int err;

- clk = clk_get_sys("smp_twd", NULL);
- if (IS_ERR(clk)) {
- pr_err("smp_twd: clock not found: %d\n", (int)PTR_ERR(clk));
- return clk;
+ if (np)
+ twd_clk = of_clk_get(np, 0);
+ else
+ twd_clk = clk_get_sys("smp_twd", NULL);
+
+ if (IS_ERR(twd_clk)) {
+ pr_err("smp_twd: clock not found: %d\n", (int)PTR_ERR(twd_clk));
+ return;
}

- err = clk_prepare_enable(clk);
+ err = clk_prepare_enable(twd_clk);
if (err) {
pr_err("smp_twd: clock failed to prepare+enable: %d\n", err);
- clk_put(clk);
- return ERR_PTR(err);
+ clk_put(twd_clk);
+ return;
}

- return clk;
+ twd_timer_rate = clk_get_rate(twd_clk);
}

/*
@@ -279,26 +281,7 @@ static int __cpuinit twd_timer_setup(struct clock_event_device *clk)
}
per_cpu(percpu_setup_called, cpu) = true;

- /*
- * This stuff only need to be done once for the entire TWD cluster
- * during the runtime of the system.
- */
- if (!common_setup_called) {
- twd_clk = twd_get_clock();
-
- /*
- * We use IS_ERR_OR_NULL() here, because if the clock stubs
- * are active we will get a valid clk reference which is
- * however NULL and will return the rate 0. In that case we
- * need to calibrate the rate instead.
- */
- if (!IS_ERR_OR_NULL(twd_clk))
- twd_timer_rate = clk_get_rate(twd_clk);
- else
- twd_calibrate_rate();
-
- common_setup_called = true;
- }
+ twd_calibrate_rate();

/*
* The following is done once per CPU the first time .setup() is
@@ -329,7 +312,7 @@ static struct local_timer_ops twd_lt_ops __cpuinitdata = {
.stop = twd_timer_stop,
};

-static int __init twd_local_timer_common_register(void)
+static int __init twd_local_timer_common_register(struct device_node *np)
{
int err;

@@ -349,6 +332,8 @@ static int __init twd_local_timer_common_register(void)
if (err)
goto out_irq;

+ twd_get_clock(np);
+
return 0;

out_irq:
@@ -372,7 +357,7 @@ int __init twd_local_timer_register(struct twd_local_timer *tlt)
if (!twd_base)
return -ENOMEM;

- return twd_local_timer_common_register();
+ return twd_local_timer_common_register(NULL);
}

#ifdef CONFIG_OF
@@ -404,7 +389,7 @@ void __init twd_local_timer_of_register(void)
goto out;
}

- err = twd_local_timer_common_register();
+ err = twd_local_timer_common_register(np);

out:
WARN(err, "twd_local_timer_of_register failed (%d)\n", err);