linux-kernel - Re: [PATCH v3 02/23] psci: Accessor for configured PSCI function IDs

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Date:   Thu, 26 Nov 2020 17:24:50 +0000
From:   Mark Rutland <mark.rutland@....com>
To:     David Brazdil <dbrazdil@...gle.com>
Cc:     kvmarm@...ts.cs.columbia.edu, Jonathan Corbet <corbet@....net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Julien Thierry <julien.thierry.kdev@...il.com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Dennis Zhou <dennis@...nel.org>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Sudeep Holla <sudeep.holla@....com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        kernel-team@...roid.com
Subject: Re: [PATCH v3 02/23] psci: Accessor for configured PSCI function IDs

On Thu, Nov 26, 2020 at 03:54:00PM +0000, David Brazdil wrote:
> Function IDs used by PSCI are configurable for v0.1 via DT/APCI. If the
> host is using PSCI v0.1, KVM's host PSCI proxy needs to use the same IDs.
> Expose the array holding the information with a read-only accessor.
> 
> Signed-off-by: David Brazdil <dbrazdil@...gle.com>
> ---
>  drivers/firmware/psci/psci.c | 16 ++++++++--------
>  include/linux/psci.h         | 10 ++++++++++
>  2 files changed, 18 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/firmware/psci/psci.c b/drivers/firmware/psci/psci.c
> index 213c68418a65..40609564595e 100644
> --- a/drivers/firmware/psci/psci.c
> +++ b/drivers/firmware/psci/psci.c
> @@ -58,16 +58,16 @@ typedef unsigned long (psci_fn)(unsigned long, unsigned long,
>  				unsigned long, unsigned long);
>  static psci_fn *invoke_psci_fn;
>  
> -enum psci_function {
> -	PSCI_FN_CPU_SUSPEND,
> -	PSCI_FN_CPU_ON,
> -	PSCI_FN_CPU_OFF,
> -	PSCI_FN_MIGRATE,
> -	PSCI_FN_MAX,
> -};
> -
>  static u32 psci_function_id[PSCI_FN_MAX];
>  
> +u32 psci_get_function_id(enum psci_function fn)
> +{
> +	if (WARN_ON_ONCE(fn < 0 || fn >= PSCI_FN_MAX))
> +		return 0;
> +
> +	return psci_function_id[fn];
> +}

I'd really like if we could namespace this with a psci_0_1_* prefix
before we expose it outside of the PSCI code. I appreciate that's a
larger change, but I reckon we only need a couple of new patches:

1) Split the ops which consume the FN ids into separate psci_0_1_*() and
   psci_0_2_*() variants, with a common __psci_*() helper that takes the
   function ID as an argument. The 0_1 variants would read the function
   ID from a variable, and the 0_2 variants would hard-code the id.

2) Replace the psci_function_id array with:

   struct psci_0_1_function_ids {
   	u32 suspend;
   	u32 cpu_on;
   	u32 cpu_off;
   	u32 migrate;
   };

   ... and remove enum psci_function entirely.

3) Add a helper which returns the entire psci_0_1_function_ids struct in
   one go. No warnings necessary.

Does that sound OK to you?

Thanks,
Mark.

> +
>  #define PSCI_0_2_POWER_STATE_MASK		\
>  				(PSCI_0_2_POWER_STATE_ID_MASK | \
>  				PSCI_0_2_POWER_STATE_TYPE_MASK | \
> diff --git a/include/linux/psci.h b/include/linux/psci.h
> index 2a1bfb890e58..5b49a5c82d6f 100644
> --- a/include/linux/psci.h
> +++ b/include/linux/psci.h
> @@ -21,6 +21,16 @@ bool psci_power_state_is_valid(u32 state);
>  int psci_set_osi_mode(bool enable);
>  bool psci_has_osi_support(void);
>  
> +enum psci_function {
> +	PSCI_FN_CPU_SUSPEND,
> +	PSCI_FN_CPU_ON,
> +	PSCI_FN_CPU_OFF,
> +	PSCI_FN_MIGRATE,
> +	PSCI_FN_MAX,
> +};
> +
> +u32 psci_get_function_id(enum psci_function fn);
> +
>  struct psci_operations {
>  	u32 (*get_version)(void);
>  	int (*cpu_suspend)(u32 state, unsigned long entry_point);
> -- 
> 2.29.2.454.gaff20da3a2-goog
>