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Message-ID: <20130110233442.GA30875@n2100.arm.linux.org.uk> Date: Thu, 10 Jan 2013 23:34:42 +0000 From: Russell King - ARM Linux <linux@....linux.org.uk> To: Mark Langsdorf <mark.langsdorf@...xeda.com> Cc: linux-kernel@...r.kernel.org, cpufreq@...r.kernel.org, linux-pm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, Rob Herring <rob.herring@...xeda.com> Subject: Re: [PATCH 1/4 v10] arm: use devicetree to get smp_twd clock 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? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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