From: Sudeep Holla <sudeep.holla@kernel•org>
To: "Aneesh Kumar K.V" <aneesh.kumar@kernel•org>
Cc: linux-coco@lists•linux.dev, linux-arm-kernel@lists•infradead.org,
linux-kernel@vger•kernel.org,
Catalin Marinas <catalin.marinas@arm•com>,
Sudeep Holla <sudeep.holla@kernel•org>,
Greg KH <gregkh@linuxfoundation•org>,
Jeremy Linton <jeremy.linton@arm•com>,
Jonathan Cameron <jic23@kernel•org>,
Lorenzo Pieralisi <lpieralisi@kernel•org>,
Mark Rutland <mark.rutland@arm•com>,
Will Deacon <will@kernel•org>,
Steven Price <steven.price@arm•com>,
Suzuki K Poulose <Suzuki.Poulose@arm•com>
Subject: Re: [PATCH v6 3/4] firmware: smccc: arm-cca-guest: Bind the TSM provider to an SMCCC device
Date: Thu, 4 Jun 2026 14:45:49 +0100 [thread overview]
Message-ID: <20260604-juicy-daft-starling-3eec1f@sudeepholla> (raw)
In-Reply-To: <yq5ase72qvwb.fsf@kernel.org>
On Thu, Jun 04, 2026 at 06:56:28PM +0530, Aneesh Kumar K.V wrote:
> Sudeep Holla <sudeep.holla@kernel•org> writes:
>
> ...
>
> > +static const struct smccc_device_info smccc_devices[] __initconst = {
> > + {
> > + .func_id = ARM_SMCCC_TRNG_VERSION,
> > + .requires_smc = false,
> > + .min_return = ARM_SMCCC_TRNG_MIN_VERSION,
> > + .device_name = "arm-smccc-trng",
> > + },
> > +};
> > +
> > +static bool __init
> > +smccc_probe_smccc_device(const struct smccc_device_info *smccc_dev)
> > +{
> > + struct arm_smccc_res res;
> > + unsigned long ret;
> > +
> > + if (!IS_ENABLED(CONFIG_ARM64))
> > + return false;
> > +
> > + if (smccc_conduit == SMCCC_CONDUIT_NONE)
> > + return false;
> > +
> > + if (smccc_dev->requires_smc && smccc_conduit != SMCCC_CONDUIT_SMC)
> > + return false;
> > +
> > + arm_smccc_1_1_invoke(smccc_dev->func_id, &res);
> > + ret = res.a0;
> > +
> > + if ((s32)ret < 0)
> > + return false;
> > +
> > + return ret >= smccc_dev->min_return;
> > +}
> > +
> >
>
> I am not sure we want the check to be as simple as ret < 0. Some
> function IDs may return input errors based on the supplied arguments
> (for example, RMI_ERROR_INPUT). In those cases, we would likely want
> this to be handled via a callback.
>
As I mentioned in response to Suzuki, we can defer that to probe of
that device. If *_VERSION, succeeds SMCCC core can add that device and
leave the rest to the core keeping the core and bus layer simple IMO.
> We also want to use conditional compilation for some function IDs.
> Given the callback approach and the #ifdefs, I wonder whether what we
> currently have is actually simpler and more flexible.”
>
I was trying to avoid conditional compilation altogether and hence the
reason for keeping it as simple as possible. Also IS_ENABLED(CONFIG_ARM64)
in above snippet must come as some condition to this generic probe.
Adding any more logic or callback defeats the bus idea here if we need
to rely/depend on multiple conditional compilation or callbacks IMO.
Let's find see if it can work with what we are adding now and may add in
near future and then decide.
--
Regards,
Sudeep
next prev parent reply other threads:[~2026-06-04 13:46 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-27 10:02 [PATCH v6 0/4] Switch Arm SMCCC firmware services to an SMCCC bus Aneesh Kumar K.V (Arm)
2026-05-27 10:02 ` [PATCH v6 1/4] firmware: smccc: Add an Arm " Aneesh Kumar K.V (Arm)
2026-06-03 18:52 ` Sudeep Holla
2026-05-27 10:02 ` [PATCH v6 2/4] firmware: hwrng: arm_smccc_trng: Register as an SMCCC device Aneesh Kumar K.V (Arm)
2026-05-27 10:02 ` [PATCH v6 3/4] firmware: smccc: arm-cca-guest: Bind the TSM provider to " Aneesh Kumar K.V (Arm)
2026-06-04 9:18 ` Suzuki K Poulose
2026-06-04 9:21 ` Sudeep Holla
2026-06-04 10:24 ` Suzuki K Poulose
2026-06-04 10:55 ` Sudeep Holla
2026-06-04 13:26 ` Aneesh Kumar K.V
2026-06-04 13:45 ` Sudeep Holla [this message]
2026-05-27 10:02 ` [PATCH v6 4/4] coco: guest: arm64: Replace dummy CCA device with sysfs ABI Aneesh Kumar K.V (Arm)
2026-06-04 12:58 ` [PATCH v6 0/4] Switch Arm SMCCC firmware services to an SMCCC bus Aneesh Kumar K.V
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