Messages in this thread Patch in this message | | | Subject | Re: [PATCH v3 7/7] clocksource/drivers/arm_arch_timer: validate arch_timer_rate | From | Lukasz Luba <> | Date | Wed, 12 Feb 2020 10:01:54 +0000 |
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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...
> + > + 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.
Regards, Lukasz
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