Messages in this thread | | | Subject | Re: [PATCH v3 7/7] clocksource/drivers/arm_arch_timer: validate arch_timer_rate | From | Lukasz Luba <> | Date | Wed, 12 Feb 2020 10:55:58 +0000 |
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On 2/12/20 10:12 AM, Marc Zyngier wrote: > On 2020-02-12 10:01, Lukasz Luba wrote: >> Hi Ionela, Valentin >> >> On 2/11/20 6:45 PM, Ionela Voinescu wrote: >>> From: Valentin Schneider <valentin.schneider@arm.com> >>> >>> Using an arch timer with a frequency of less than 1MHz can result in an >>> incorrect functionality of the system which assumes a reasonable rate. >>> >>> One example is the use of activity monitors for frequency invariance >>> which uses the rate of the arch timer as the known rate of the constant >>> cycle counter in computing its ratio compared to the maximum frequency >>> of a CPU. For arch timer frequencies less than 1MHz this ratio could >>> end up being 0 which is an invalid value for its use. >>> >>> Therefore, warn if the arch timer rate is below 1MHz which contravenes >>> the recommended architecture interval of 1 to 50MHz. >>> >>> Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com> >>> Cc: Mark Rutland <mark.rutland@arm.com> >>> Cc: Marc Zyngier <maz@kernel.org> >>> --- >>> drivers/clocksource/arm_arch_timer.c | 18 +++++++++++++++--- >>> 1 file changed, 15 insertions(+), 3 deletions(-) >>> >>> diff --git a/drivers/clocksource/arm_arch_timer.c >>> b/drivers/clocksource/arm_arch_timer.c >>> index 9a5464c625b4..4faa930eabf8 100644 >>> --- a/drivers/clocksource/arm_arch_timer.c >>> +++ b/drivers/clocksource/arm_arch_timer.c >>> @@ -885,6 +885,17 @@ static int arch_timer_starting_cpu(unsigned int >>> cpu) >>> return 0; >>> } >>> +static int validate_timer_rate(void) >>> +{ >>> + if (!arch_timer_rate) >>> + return -EINVAL; >>> + >>> + /* Arch timer frequency < 1MHz can cause trouble */ >>> + WARN_ON(arch_timer_rate < 1000000); >> >> I don't see a big value of having a patch just to add one extra warning, >> in a situation which we handle in our code with in 6/7 with: >> >> + if (!ratio) { >> + pr_err("System timer frequency too low.\n"); >> + return -EINVAL; >> + } >> >> Furthermore, the value '100000' here is because of our code and >> calculation in there, so it does not belong to arch timer. Someone >> might ask why it's not 200000 or a define in our header... >> Or questions asking why do you warn when that arch timer and cpu is not >> AMU capable... > > Because, as the commit message outlines it, such a frequency is terribly > out of spec?
I don't see in the RM that < 1MHz is terribly out of spec. 'Frequency Increments at a fixed frequency, typically in the range 1-50MHz. Can support one or more alternative operating modes in which it increments by larger amounts at a lower frequency, typically for power-saving.'
There is even an example how to operate at 20kHz and increment by 500.
I don't know the code if it's supported, thought.
> >> >>> + >>> + return 0; >>> +} >>> + >>> /* >>> * For historical reasons, when probing with DT we use whichever >>> (non-zero) >>> * rate was probed first, and don't verify that others match. If >>> the first node >>> @@ -900,7 +911,7 @@ static void arch_timer_of_configure_rate(u32 >>> rate, struct device_node *np) >>> arch_timer_rate = rate; >>> /* Check the timer frequency. */ >>> - if (arch_timer_rate == 0) >>> + if (validate_timer_rate()) >>> pr_warn("frequency not available\n"); >>> } >>> @@ -1594,9 +1605,10 @@ static int __init >>> arch_timer_acpi_init(struct acpi_table_header *table) >>> * CNTFRQ value. This *must* be correct. >>> */ >>> arch_timer_rate = arch_timer_get_cntfrq(); >>> - if (!arch_timer_rate) { >>> + ret = validate_timer_rate(); >>> + if (ret) { >>> pr_err(FW_BUG "frequency not available.\n"); >>> - return -EINVAL; >>> + return ret; >>> } >>> arch_timer_uses_ppi = arch_timer_select_ppi(); >>> >> >> Lastly, this is arch timer. >> To increase chances of getting merge soon, I would recommend to drop >> the patch from this series. > > And? It seems to address a potential issue where the time frequency > is out of spec, and makes sure we don't end up with additional problems > in the AMU code.
This patch just prints warning, does not change anything in booting or in any code related to AMU.
> > On its own, it is perfectly sensible and could be merged as part of this > series with my > > Acked-by: Marc Zyngier <maz@kernel.org> > > M.
Regards, Lukasz
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