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    SubjectRe: [PATCH] firmware/psci: Don't register with debugfs if PSCI isn't available
    On Thu, Jan 05, 2023 at 09:08:34AM +0000, Marc Zyngier wrote:
    > 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@marcan.st>
    > Signed-off-by: Marc Zyngier <maz@kernel.org>
    > Cc: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
    > Cc: Mark Brown <broonie@kernel.org>
    > Cc: Ulf Hansson <ulf.hansson@linaro.org>
    > Cc: Arnd Bergmann <arnd@arndb.de>
    > Cc: Mark Rutland <mark.rutland@arm.com>
    > Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>

    Acked-by: Mark Rutland <mark.rutland@arm.com>

    Mark.

    > ---
    > 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
    >

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