linux-kernel - [PATCH] arm64: arch_timer: XGene-1 has 31 bit, not 32 bit, arch timer.

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Message-ID: <20221021153424.GA25677@zipoli.concurrent-rt.com>
Date:   Fri, 21 Oct 2022 11:34:24 -0400
From:   Joe Korty <joe.korty@...current-rt.com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Subject: [PATCH] arm64: arch_timer: XGene-1 has 31 bit, not 32 bit, arch
 timer.

arm64: XGene-1 has a 31 bit, not a 32 bit, arch timer.

Fixes: 012f188504528b8cb32f441ac3bd9ea2eba39c9e ("clocksource/drivers/arm_arch_timer:
  Work around broken CVAL implementations")

Testing:
  On an 8-cpu Mustang, the following sequence no longer locks up the system:

     echo 0 >/proc/sys/kernel/watchdog
     for i in {0..7}; do taskset -c $i echo hi there $i; done

Stable:
  To be applied to 5.16 and above, once accepted by mainline.

Signed-off-by: Joe Korty <joe.korty@...current-rt.com>

Index: b/drivers/clocksource/arm_arch_timer.c
===================================================================
--- a/drivers/clocksource/arm_arch_timer.c
+++ b/drivers/clocksource/arm_arch_timer.c
@@ -805,7 +805,7 @@ static u64 __arch_timer_check_delta(void
 	const struct midr_range broken_cval_midrs[] = {
 		/*
 		 * XGene-1 implements CVAL in terms of TVAL, meaning
-		 * that the maximum timer range is 32bit. Shame on them.
+		 * that the maximum timer range is 31bit. Shame on them.
 		 */
 		MIDR_ALL_VERSIONS(MIDR_CPU_MODEL(ARM_CPU_IMP_APM,
 						 APM_CPU_PART_POTENZA)),
@@ -813,8 +813,8 @@ static u64 __arch_timer_check_delta(void
 	};
 
 	if (is_midr_in_range_list(read_cpuid_id(), broken_cval_midrs)) {
-		pr_warn_once("Broken CNTx_CVAL_EL1, limiting width to 32bits");
-		return CLOCKSOURCE_MASK(32);
+		pr_warn_once("Broken CNTx_CVAL_EL1, limiting width to 31bits");
+		return CLOCKSOURCE_MASK(31);
 	}
 #endif
 	return CLOCKSOURCE_MASK(arch_counter_get_width());