Subject: Re: [PATCH v1 01/24] psci: Accessor for configured PSCI version

From: Marc Zyngier <[email-masked]>
Date: Tue, 10 Nov 2020 14:43:01 +0000

On 2020-11-09 11:32, David Brazdil wrote:
> The version of PSCI that the kernel should use to communicate with
> firmware is typically obtained from probing PSCI_VERSION. However, that
> doesn't work for PSCI v0.1 where the host gets the information from
> DT/ACPI, or if PSCI is not supported / was disabled.
> 
> KVM's host PSCI proxy needs to be configured with the same version
> used by the host driver. Expose the PSCI version used by the host
> with a read-only accessor.
> 
> Signed-off-by: David Brazdil <[email-masked]>
> ---
>  drivers/firmware/psci/psci.c | 11 +++++++++++
>  include/linux/psci.h         |  8 ++++++++
>  2 files changed, 19 insertions(+)
> 
> diff --git a/drivers/firmware/psci/psci.c 
> b/drivers/firmware/psci/psci.c
> index 00af99b6f97c..bc1b2d60fdbf 100644
> --- a/drivers/firmware/psci/psci.c
> +++ b/drivers/firmware/psci/psci.c
> @@ -49,6 +49,13 @@ static int resident_cpu = -1;
>  struct psci_operations psci_ops;
>  static enum arm_smccc_conduit psci_conduit = SMCCC_CONDUIT_NONE;
> 
> +static int driver_version = PSCI_VERSION(0, 0);
> +
> +int psci_driver_version(void)
> +{
> +	return driver_version;
> +}
> +
>  bool psci_tos_resident_on(int cpu)
>  {
>  	return cpu == resident_cpu;
> @@ -461,6 +468,8 @@ static int __init psci_probe(void)
>  		return -EINVAL;
>  	}
> 
> +	driver_version = ver;
> +
>  	psci_0_2_set_functions();
> 
>  	psci_init_migrate();
> @@ -514,6 +523,8 @@ static int __init psci_0_1_init(struct device_node 
> *np)
> 
>  	pr_info("Using PSCI v0.1 Function IDs from DT\n");
> 
> +	driver_version = PSCI_VERSION(0, 1);
> +
>  	if (!of_property_read_u32(np, "cpu_suspend", &id)) {
>  		psci_function_id[PSCI_FN_CPU_SUSPEND] = id;
>  		psci_ops.cpu_suspend = psci_cpu_suspend;
> diff --git a/include/linux/psci.h b/include/linux/psci.h
> index 2a1bfb890e58..5b5dcf176aa6 100644
> --- a/include/linux/psci.h
> +++ b/include/linux/psci.h
> @@ -21,6 +21,14 @@ bool psci_power_state_is_valid(u32 state);
>  int psci_set_osi_mode(bool enable);
>  bool psci_has_osi_support(void);
> 
> +/**
> + * The version of the PSCI specification followed by the driver.
> + * This is equivalent to calling PSCI_VERSION except:
> + *   (a) it also works for PSCI v0.1, which does not support 
> PSCI_VERSION, and
> + *   (b) it is set to v0.0 if the PSCI driver was not initialized.
> + */
> +int psci_driver_version(void);
> +
>  struct psci_operations {
>  	u32 (*get_version)(void);
>  	int (*cpu_suspend)(u32 state, unsigned long entry_point);

I still maintain that populating .get_version in all cases instead of
duplicating an existing functionality is a better outcome. PSCI not
supported would be implied by .get_version being NULL.

What breaks?

         M.
-- 
Jazz is not dead. It just smells funny...

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