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

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Message-ID: <Y7bLz/1ISoKdNoLW@FVFF77S0Q05N>
Date:   Thu, 5 Jan 2023 13:08:31 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     Marc Zyngier <maz@...nel.org>
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        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>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>
Subject: Re: [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@...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>

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