[PATCH v20 08/17] clocksource/drivers/arm_arch_timer: Rework counter frequency detection.

On Wed, Feb 01, 2017 at 02:43:02AM +0800, Fu Wei wrote:

On 31 January 2017 at 01:49, Mark Rutland [off-list ref] wrote:

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On Thu, Jan 26, 2017 at 01:49:03PM +0800, Fu Wei wrote:

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On 26 January 2017 at 01:25, Mark Rutland [off-list ref] wrote:

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On Wed, Jan 25, 2017 at 02:46:12PM +0800, Fu Wei wrote:

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On 25 January 2017 at 01:24, Mark Rutland [off-list ref] wrote:

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On Wed, Jan 18, 2017 at 09:25:32PM +0800, fu.wei at linaro.org wrote:

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From: Fu Wei <redacted>

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But according to another document(ARMv8-A Foundation Platform User
Guide  ARM DUI0677K),
Table 3-2 ARMv8-A Foundation Platform memory map (continued)

AP_REFCLK CNTBase0, Generic Timer 64KB   S
AP_REFCLK CNTBase1, Generic Timer 64KB   S/NS

Dose it means the timer frame 0 can be accessed in SECURE status  only,
and the timer frame 1 can be accessed in both status?

That does appear to be what it says.

I assume in this case CNTCTLBase.CNTSAR<0> is RES0.

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And because Linux kernel is running on Non-secure EL1, so should we
skip "SECURE" timer in Linux?

I guess you mean by checking the GTx Common flags, to see if the timer
is secure? Yes, we must skip those.

Yes, exactly.

I think we can check the  GTx Common flags, if the timer is set as
SECURE, this driver should just skip this timer.

I completely agree that we must skip these.

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Looking further at this, the ACPI spec is sorely lacking any statement
as to the configuration of CNTCTLBase.{CNTSAR,CNTTIDR,CNTACR}, so it's
not clear if we can access anything in a frame, even if it is listed as
being a non-secure timer.

I think we need a stronger statement here. Otherwise, we will encounter
problems. Linux currently assumes that CNTCTLBase.CNTACR<N> is
writeable, given a non-secure frame N. This is only the case if
CNTCTLBase.CNTSAR.NS<N> == 1.

the original driver has checked these registers, but the problem is:
What if the timer frame is designed to be a secure timer, all the
register in this frame is only can be accessed in secure status, just
like foundation model?
Note: for foundation model, Please check Table 3-1 Access permissions
of 3.1 ARMv8-A Foundation Platform memory map in ARMv8-A Foundation
Platform User Guide

So I think we should check the GTDT first, if it's not a secure timer,
then we can go on checking CNTSAR. :-)

I've clearly confused matters here. I completely agree that we must skip
timers the GTDT descrbies as secure.

My complaint here is that the spec does not explicitly state that
CNTCTLBase.CNTSAR.NS<N> must be set for timers *not* marked as secure
(though I believe that is the intent). That is a spec issue, not a code
issue.

We unfortunately can't check CNTNSAR, as it is secure-only. :(

Thanks,
Mark.