linux-kernel - [PATCH v6 7/7] clocksource/drivers/arm_arch_timer: validate arch_timer

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Message-Id: <20200305090627.31908-8-ionela.voinescu@arm.com>
Date:   Thu,  5 Mar 2020 09:06:27 +0000
From:   Ionela Voinescu <ionela.voinescu@....com>
To:     catalin.marinas@....com, will@...nel.org, mark.rutland@....com,
        maz@...nel.org, suzuki.poulose@....com, sudeep.holla@....com,
        lukasz.luba@....com, valentin.schneider@....com,
        dietmar.eggemann@....com, rjw@...ysocki.net,
        pkondeti@...eaurora.org, ionela.voinescu@....com
Cc:     peterz@...radead.org, mingo@...hat.com, vincent.guittot@...aro.org,
        viresh.kumar@...aro.org, linux-arm-kernel@...ts.infradead.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pm@...r.kernel.org
Subject: [PATCH v6 7/7] 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.

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