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Date:   Thu, 26 Nov 2020 17:29:30 +0000
From:   David Brazdil <dbrazdil@google.com>
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     kvmarm@lists.cs.columbia.edu, Jonathan Corbet <corbet@lwn.net>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Marc Zyngier <maz@kernel.org>,
        James Morse <james.morse@arm.com>,
        Julien Thierry <julien.thierry.kdev@gmail.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Dennis Zhou <dennis@kernel.org>, Tejun Heo <tj@kernel.org>,
        Christoph Lameter <cl@linux.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
        Sudeep Holla <sudeep.holla@arm.com>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        kernel-team@android.com
Subject: Re: [PATCH v3 02/23] psci: Accessor for configured PSCI function IDs
Message-ID: <20201126172930.i63yemxpc5r3mqpq@google.com>
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 <20201126172450.GC38486@C02TD0UTHF1T.local>
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Hey Mark,

On Thu, Nov 26, 2020 at 05:24:50PM +0000, Mark Rutland wrote:
> 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@google.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?

Sure, sounds easy enough and 2) is in line with how I structured the handlers
in KVM.

Thanks,
David