[PATCH v5 7/7] clocksource/drivers/arm_arch_timer: validate arch_timer_rate

Ionela Voinescu
2020-02-26T13:31:07Z

Using an arch timer with a frequency of less than 1MHz can potentially
result in incorrect functionality in systems that assume a reasonable
rate of the arch timer of 1 to 50MHz, described as typical in the
architecture specification.

Therefore, warn if the arch timer rate is below 1MHz, which is
considered atypical and worth emphasizing.

Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Suggested-by: Valentin Schneider <valentin.schneider@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
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);
+
+ 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();
--
2.17.1