Hi Mark,

On 17 January 2017 at 01:50, Mark Rutland [off-list ref] wrote:

On Wed, Dec 21, 2016 at 02:45:54PM +0800, fu.wei at linaro.org wrote:

quoted

From: Fu Wei <redacted>

Currently, the counter frequency detection call(arch_timer_detect_rate)
combines all the ways to get counter frequency: device-tree property,
system coprocessor register, MMIO timer. But in the most of use cases,
we don't need all the ways to try:
For example, reading device-tree property will be needed only when
system boot with device-tree, getting frequency from MMIO timer register
will beneeded only when we init MMIO timer.

This patch separates paths to determine frequency:
Separate out device-tree code, keep them in device-tree init function.

Splitting these out makes sense to me.

OK , will do

quoted

Separate out the MMIO frequency and the sysreg frequency detection call,
and use the appropriate one for the counter.

quoted

Signed-off-by: Fu Wei <redacted>
Tested-by: Xiongfeng Wang <redacted>
---
 drivers/clocksource/arm_arch_timer.c | 49 +++++++++++++++++++++++-------------
 1 file changed, 31 insertions(+), 18 deletions(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index c7b4482..9a1f138 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c

@@ -488,27 +488,31 @@ static int arch_timer_starting_cpu(unsigned int cpu)
      return 0;
 }

-static void
-arch_timer_detect_rate(void __iomem *cntbase, struct device_node *np)
+static void arch_timer_detect_rate(void)
 {
-     /* Who has more than one independent system counter? */
-     if (arch_timer_rate)
-             return;
+     /*
+      * Try to get the timer frequency from
+      * cntfrq_el0(system coprocessor register).
+      */
+     if (!arch_timer_rate)
+             arch_timer_rate = arch_timer_get_cntfrq();
+
+     /* Check the timer frequency. */
+     if (!arch_timer_rate)
+             pr_warn("frequency not available\n");
+}

+static void arch_timer_mem_detect_rate(void __iomem *cntbase)
+{
      /*
-      * Try to determine the frequency from the device tree or CNTFRQ,
-      * if ACPI is enabled, get the frequency from CNTFRQ ONLY.
+      * Try to determine the frequency from
+      * CNTFRQ in memory-mapped timer.
       */
-     if (!acpi_disabled ||
-         of_property_read_u32(np, "clock-frequency", &arch_timer_rate)) {
-             if (cntbase)
-                     arch_timer_rate = readl_relaxed(cntbase + CNTFRQ);
-             else
-                     arch_timer_rate = arch_timer_get_cntfrq();
-     }
+     if (!arch_timer_rate)
+             arch_timer_rate = readl_relaxed(cntbase + CNTFRQ);

      /* Check the timer frequency. */
-     if (arch_timer_rate == 0)
+     if (!arch_timer_rate)

I think you mean this one, this is for keeping consistency with
arch_timer_detect_rate.

quoted

              pr_warn("frequency not available\n");
 }

There's a subtle change in behaviour here. Previously for ACPI we'd only
ever use the sysreg CNTFRQ value for arch_timer_rate, whereas now we
might use the MMIO timer rate. Maybe that's not a big deal, but I will
need to think.

Generally, the logic to determine the rate is fairly gnarly regardless.

It would be nice if we could split the MMIO and sysreg rates entirely,

Yes, I am doing this way,

For sysreg rates,
static void arch_timer_detect_rate(void)
{
/*
* Try to get the timer frequency from
* cntfrq_el0(system coprocessor register).
*/
if (!arch_timer_rate)
arch_timer_rate = arch_timer_get_cntfrq();

/* Check the timer frequency. */
if (!arch_timer_rate)
pr_warn("frequency not available\n");
}

For MMIO timer,
static void arch_timer_mem_detect_rate(void __iomem *cntbase)
{
/*
* Try to determine the frequency from
* CNTFRQ in memory-mapped timer.
*/
if (!arch_timer_rate)
arch_timer_rate = readl_relaxed(cntbase + CNTFRQ);

/* Check the timer frequency. */
if (!arch_timer_rate)
pr_warn("frequency not available\n");
}

in arch_time_*_init, only call  arch_timer_detect_rate,
in arch_timer_mem_init, only call arch_timer_mem_detect_rate.

But you are right, this is fairly gnarly regardless.

and kill the implicit relationship between the two, or at least make one
canonical and warn if the two differ.

So I think maybe we can do this:

static void __arch_timer_determine_rate(u32 rate)
{
/* Check the timer frequency. */
if (!arch_timer_rate)
if (rate)
arch_timer_rate = rate;
else
pr_warn("frequency not available\n");
else if (arch_timer_rate != rate)
pr_warn("got different frequency, keep original.\n");
}

static void arch_timer_detect_rate(void)
{
/*
* Try to get the timer frequency from
* cntfrq_el0(system coprocessor register).
*/
__arch_timer_determine_rate(arch_timer_get_cntfrq());
}

static void arch_timer_mem_detect_rate(void __iomem *cntbase)
{
/*
* Try to get the timer frequency from
* CNTFRQ in the MMIO timer.
*/
__arch_timer_determine_rate(readl_relaxed(cntbase + CNTFRQ));
}

any thought?

Thanks,
Mark.

-- 
Best regards,

Fu Wei
Software Engineer
Red Hat