[PATCH v16 07/15] clocksource/drivers/arm_arch_timer: Refactor arch_timer_detect_rate to keep dt code in *_of_init

Hi Mark

On 19 November 2016 at 03:52, Mark Rutland [off-list ref] wrote:

On Wed, Nov 16, 2016 at 09:49:00PM +0800, fu.wei at linaro.org wrote:

quoted

From: Fu Wei <redacted>

The patch refactor original arch_timer_detect_rate function:
    (1) Separate out device-tree code, keep them in device-tree init
    function:
        arch_timer_of_init,
        arch_timer_mem_init;

Please write a real commit message.

Sorry, will do

Since this patch will be separated into two patches.
the first patch will be separating out device-tree code, so commit
message can be:
-----------------
clocksource/drivers/arm_arch_timer: Separate out device-tree code from
arch_timer_detect_rate

Currently, the arch_timer_detect_rate can get system counter frequency
from device-tree, sysreg timers and MMIO timers. This is unnecessary and
confusing. For ACPI, we don't need a function included device-tree code.

This patch factors the device-tree related code out into device-tree
init function:
arch_timer_of_init and arch_timer_mem_init.
-----------------

the second patch will be split arch_timer_detect_rate in two, one is
for the MMIO timer,
another is for the CP15 timers, so commit message can be:
-----------------
clocksource/drivers/arm_arch_timer:split arch_timer_detect_rate for
the MMIO and CP15 timers

The arch_timer_detect_rate can get system counter frequency sysreg timers and
MMIO timers. This is unnecessary. For initializing sysreg timers, we
shouldn't try to
access MMIO timers.

This patch split arch_timer_detect_rate into two function:
arch_timer_detect_rate and arch_timer_mem_detect_rate.
-----------------

Please correct me if these commit message are inappropriate.
Great thanks

quoted

    (2) Improve original mechanism, if getting from memory-mapped timer
    fail, try arch_timer_get_cntfrq() again.

This is *not* a refactoring. It's completely unrelated to the supposed
refactoring from point (1), and if necessary, should be a separate
patch.

*Why* are you maknig this change? Does some ACPI platform have an MMIO
timer with an ill-configured CNTFRQ register? If so, report that to the
vendor. Don't add yet another needless bodge.

I'd really like to split the MMIO and CP15 timers, and this is yet
another hack that'll make it harder to do so.

you are right, I should split this founction for the MMIO and CP15 timers

quoted

Signed-off-by: Fu Wei <redacted>
---
 drivers/clocksource/arm_arch_timer.c | 45 +++++++++++++++++++++++-------------
 1 file changed, 29 insertions(+), 16 deletions(-)

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index af22953..fe4e812 100644
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c

@@ -487,27 +487,31 @@ 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 __iomem *cntbase)
 {
      /* Who has more than one independent system counter? */
      if (arch_timer_rate)
              return;
-
      /*
-      * Try to determine the frequency from the device tree or CNTFRQ,
-      * if ACPI is enabled, get the frequency from CNTFRQ ONLY.
+      * If we got memory-mapped timer(cntbase != NULL),
+      * try to determine the frequency from CNTFRQ in memory-mapped timer.
       */

*WHY* ?

If we're sharing arch_timer_rate across MMIO and sysreg timers, the
sysreg value is alreayd sufficient.

yes, we are sharing arch_timer_rate across MMIO and sysreg timers,
But for booting with device-tree, we can't make sure which timer will
be initialized first,
so we may need :
       if (arch_timer_rate)
               return;

If we're not, they should be completely independent.

quoted

-     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 (cntbase)
+             arch_timer_rate = readl_relaxed(cntbase + CNTFRQ);
+     /*
+      * Because in a system that implements both Secure and
+      * Non-secure states, CNTFRQ is only accessible in Secure state.

That's true for the CNTCTLBase frame, but that doesn't matter.

The CNTBase<n> frames should have a readable CNTFRQ.

Sorry, maybe I misunderstand the ARM doc, but in I3.5.7
CNTFRQ, Counter-timer Frequency, it says:
-----------------
For the CNTBaseN and CNTEL0BaseN frames:
? A RO copy of CNTFRQ is implemented in the CNTBaseN frame when both:
  ? CNTACR<n>.RFRQ is 1.
  ? Bit[0] of CNTTIDR.Frame<n> is 1.
  Otherwise the encoding in CNTBaseN is RES 0.
? When CNTFRQ is RO in the CNTBaseN frame, it is also RO in the
CNTEL0BaseN frame
  if bit[2] of CNTTIDR.Frame<n> is 1 and either:
  ? The value of CNTEL0ACR.EL0VCTEN is 1.
  ? The value of CNTEL0ACR.EL0PCTEN is 1.
  Otherwise the CNTFRQ encoding in CNTEL0BaseN frame is RES 0.
In a system that implements both Secure and Non-secure states, this
register is only accessible by
Secure accesses.
-----------------

So I think this is for both  CNTBaseN and CNTEL0BaseN frames?
Please correct me.

When I tested my patchset on Foundation model, I got "0" from
CNTBaseN's CNTFRQ, so mybe is not implemented?

quoted

+      * So the operation above may fail, even if (cntbase != NULL),
+      * especially on ARM64.
+      * In this case, we can try cntfrq_el0(system coprocessor register).
+      */
+     if (!arch_timer_rate)
+             arch_timer_rate = arch_timer_get_cntfrq();
+     else
+             return;

Urrgh.

Please have separate paths to determine the MMIO frequency and the
sysreg frequency, and use the appropriate one for the counter you want
to know the frequency of.

OK, will do

Thanks,
Mark.

-- 
Best regards,

Fu Wei
Software Engineer
Red Hat