clocksource/drivers/arm_arch_timer: validate arch_timer_rate

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.

Suggested-by: Valentin Schneider <valentin.schneider@arm.com>
Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com>
Acked-by: Marc Zyngier <maz@kernel.org>
Cc: Marc Zyngier <maz@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

diff --git a/drivers/clocksource/arm_arch_timer.c b/drivers/clocksource/arm_arch_timer.c
index 9a5464c625b45a04d7f52d6bc8b96bbfd99066b8..4faa930eabf8fbd3a8f2833876f552a37677e916 100644 (file)
--- 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();