[PATCH v3 7/7] clocksource/drivers/arm_arch_timer: validate arch_timer_rate
From: Ionela Voinescu <hidden>
Date: 2020-02-11 18:46:48
Also in:
linux-doc, linux-pm, lkml
Subsystem:
arm architected timer driver, clocksource, clockevent drivers, the rest · Maintainers:
Mark Rutland, Marc Zyngier, Daniel Lezcano, Thomas Gleixner, Linus Torvalds
From: Valentin Schneider <redacted> 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 <redacted> 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
_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel