linux-kernel - Re: [PATCH v5] clocksource:arm_global_timer: Add ARM global timer support.

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Message-ID: <51C956F7.2040502@st.com>
Date:	Tue, 25 Jun 2013 09:38:15 +0100
From:	Srinivas KANDAGATLA <srinivas.kandagatla@...com>
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	linux-doc@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	Will Deacon <will.deacon@....com>,
	linux-kernel@...r.kernel.org,
	Rob Herring <rob.herring@...xeda.com>,
	Stuart Menefy <stuart.menefy@...com>,
	John Stultz <john.stultz@...aro.org>,
	Grant Likely <grant.likely@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v5] clocksource:arm_global_timer: Add ARM global timer
 support.

Thankyou for the comments.
On 24/06/13 23:08, Stephen Boyd wrote:
> On 06/24/13 08:53, Srinivas KANDAGATLA wrote:
>> +#include <linux/clkdev.h>
> 
> Why do you need this include?
> 
>> +#include <asm/mach/irq.h>
> 
> And this one?
Removed them.
> 
>> +static u64 gt_counter_read(void)
>> +{
>> +	u64 counter;
>> +	u32 lower;
>> +	u32 upper, old_upper;
>> +
>> +	upper = readl_relaxed(gt_base + GT_COUNTER1);
>> +	do {
>> +		old_upper = upper;
>> +		lower = readl_relaxed(gt_base + GT_COUNTER0);
>> +		upper = readl_relaxed(gt_base + GT_COUNTER1);
> [snip]
>> +static void gt_compare_set(unsigned long delta, int periodic)
>> +{
>> +	u64 counter = gt_counter_read();
>> +	unsigned long ctrl = readl(gt_base + GT_CONTROL);
>> +
>> +	counter += delta;
>> +	ctrl &=  ~(GT_CONTROL_COMP_ENABLE | GT_CONTROL_IRQ_ENABLE);
>> +
>> +	writel(ctrl, gt_base + GT_CONTROL);
>> +	writel(lower_32_bits(counter), gt_base + GT_COMP0);
>> +	writel(upper_32_bits(counter), gt_base + GT_COMP1);
>> +
>> +	if (periodic) {
>> +		writel(delta, gt_base + GT_AUTO_INC);
>> +		ctrl |= GT_CONTROL_AUTO_INC;
>> +	}
>> +
>> +	ctrl |= GT_CONTROL_COMP_ENABLE | GT_CONTROL_IRQ_ENABLE;
>> +	writel(ctrl, gt_base + GT_CONTROL);
>> +}
> 
> Why is there a mix of the relaxed and non-relaxed io accessors?

gt_counter_read will be used very frequently, so using relaxed can
reduce latencies involved in memory barriers.

> 
>> +#ifdef CONFIG_CLKSRC_ARM_GLOBAL_TIMER_SCHED_CLOCK
>> +static u32 gt_sched_clock_read(void)
> 
> notrace
> 
Ok, fixed it.
>> +{
>> +	if (!gt_base)
>> +		return 0;
> 
> Seems impossible? Remove this check?
Yep, I agree this case is impossible in the code flow.
> 

Thanks,
srini
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