linux-kernel - [PATCH] firmware/psci: Don't register with debugfs if PSCI isn't available

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Message-Id: <20230105090834.630238-1-maz@kernel.org>
Date:   Thu,  5 Jan 2023 09:08:34 +0000
From:   Marc Zyngier <maz@...nel.org>
To:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     Hector Martin <marcan@...can.st>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        Mark Rutland <mark.rutland@....com>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>
Subject: [PATCH] firmware/psci: Don't register with debugfs if PSCI isn't available

Contrary to popular belief, PSCI is not a universal property of an
ARM/arm64 system. There is a garden variety of systems out there
that don't (or even cannot) implement it.

I'm the first one deplore such a situation, but hey...

On such systems, a "cat /sys/kernel/debug/psci" results in
fireworks, as no invocation callback is registered.

Check for the invoke_psci_fn and psci_ops.get_version pointers
before registering with the debugfs subsystem, avoiding the
issue altogether.

Fixes: 3137f2e60098 ("firmware/psci: Add debugfs support to ease debugging")
Reported-by: Hector Martin <marcan@...can.st>
Signed-off-by: Marc Zyngier <maz@...nel.org>
Cc: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc: Mark Brown <broonie@...nel.org>
Cc: Ulf Hansson <ulf.hansson@...aro.org>
Cc: Arnd Bergmann <arnd@...db.de>
Cc: Mark Rutland <mark.rutland@....com>
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>
---
 drivers/firmware/psci/psci.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
index e7bcfca4159f..447ee4ea5c90 100644
--- a/drivers/firmware/psci/psci.c
+++ b/drivers/firmware/psci/psci.c
@@ -440,6 +440,9 @@ static const struct file_operations psci_debugfs_ops = {
 
 static int __init psci_debugfs_init(void)
 {
+	if (!invoke_psci_fn || !psci_ops.get_version)
+		return 0;
+
 	return PTR_ERR_OR_ZERO(debugfs_create_file("psci", 0444, NULL, NULL,
 						   &psci_debugfs_ops));
 }
-- 
2.34.1