Re: [PATCH v4] firmware: smccc: Support optional Arm SMC SOC_ID name

Sudeep Holla
2025-03-03T14:45:32Z

On Mon, Mar 03, 2025 at 02:18:05PM +0000, Mark Rutland wrote:
> Hi Paul,
>
> This looks generally good with a couple of minor nits.
>
> On Tue, Feb 18, 2025 at 04:59:32PM -0800, Paul Benoit wrote:
> > Issue Number 1.6 of the Arm SMC Calling Convention introduces an optional
> > SOC_ID name string. If implemented, point the 'machine' field of the SoC
> > Device Attributes at this string so that it will appear under
> > /sys/bus/soc/devices/soc0/machine.
> >
> > On Arm SMC compliant SoCs, this will allow things like 'lscpu' to
> > eventually get a SoC provider model name from there rather than each
> > tool/utility needing to get a possibly inconsistent, obsolete, or incorrect
> > model/machine name from its own hardcoded model/machine name table.
> >
> > Signed-off-by: Paul Benoit <paul@os.amperecomputing.com>
> > Cc: Mark Rutland <mark.rutland@arm.com>
> > Cc: Lorenzo Pieralisi <lpieralisi@kernel.org>
> > Cc: Sudeep Holla <sudeep.holla@arm.com>
> > Cc: linux-arm-kernel@lists.infradead.org
> > ---

[...]

> > +static char __init *smccc_soc_name_init(void)
> > +{
> > + struct arm_smccc_1_2_regs args;
> > + struct arm_smccc_1_2_regs res;
> > + size_t len;
> > +
> > + /*
> > + * Issue Number 1.6 of the Arm SMC Calling Convention
> > + * specification introduces an optional "name" string
> > + * to the ARM_SMCCC_ARCH_SOC_ID function. Fetch it if
> > + * available.
> > + */
> > + args.a0 = ARM_SMCCC_ARCH_SOC_ID;
> > + args.a1 = 2; /* SOC_ID name */
> > + arm_smccc_1_2_invoke(&args, &res);
> > + if ((u32)res.a0 == 0) {
> > + const unsigned int regsize = sizeof(res.a1);
> > +
> > + /*
> > + * Copy res.a1..res.a17 to the smccc_soc_id_name string
> > + * 8 bytes at a time. As per Issue 1.6 of the Arm SMC
> > + * Calling Convention, the string will be NUL terminated
> > + * and padded, from the end of the string to the end of the
> > + * 136 byte buffer, with NULs.
> > + */
> > + str_fragment_from_reg(smccc_soc_id_name + 0*regsize, res.a1);
> > + str_fragment_from_reg(smccc_soc_id_name + 1*regsize, res.a2);
> > + str_fragment_from_reg(smccc_soc_id_name + 2*regsize, res.a3);
> > + str_fragment_from_reg(smccc_soc_id_name + 3*regsize, res.a4);
> > + str_fragment_from_reg(smccc_soc_id_name + 4*regsize, res.a5);
> > + str_fragment_from_reg(smccc_soc_id_name + 5*regsize, res.a6);
> > + str_fragment_from_reg(smccc_soc_id_name + 6*regsize, res.a7);
> > + str_fragment_from_reg(smccc_soc_id_name + 7*regsize, res.a8);
> > + str_fragment_from_reg(smccc_soc_id_name + 8*regsize, res.a9);
> > + str_fragment_from_reg(smccc_soc_id_name + 9*regsize, res.a10);
> > + str_fragment_from_reg(smccc_soc_id_name + 10*regsize, res.a11);
> > + str_fragment_from_reg(smccc_soc_id_name + 11*regsize, res.a12);
> > + str_fragment_from_reg(smccc_soc_id_name + 12*regsize, res.a13);
> > + str_fragment_from_reg(smccc_soc_id_name + 13*regsize, res.a14);
> > + str_fragment_from_reg(smccc_soc_id_name + 14*regsize, res.a15);
> > + str_fragment_from_reg(smccc_soc_id_name + 15*regsize, res.a16);
> > + str_fragment_from_reg(smccc_soc_id_name + 16*regsize, res.a17);
>
> Please get rid of 'regsize' and use '8' directly. This only exists for
> arm64, where the registeres are 8 bytes, and the comment immediately
> above refers to "8 bytes" specifically anyway, so 'regsize' only serves
> to make this harder to read.
>
> It'd be a bit clearer as:
>
> str_fragment_from_reg(smccc_soc_id_name + 8 * 0, res.a1);
> str_fragment_from_reg(smccc_soc_id_name + 8 * 1, res.a2);
> ...
> str_fragment_from_reg(smccc_soc_id_name + 8 * 15, res.a16);
> str_fragment_from_reg(smccc_soc_id_name + 8 * 16, res.a17);
>
> Sudeep, are you happy to fix that up when applying?
>
> > +
> > + len = strnlen(smccc_soc_id_name, sizeof(smccc_soc_id_name));
> > + if (len) {
> > + if (len == sizeof(smccc_soc_id_name))
> > + pr_warn(FW_BUG "Ignoring improperly formatted Name\n");
>
> It's odd that 'Name' is capitalized here. Not a big deal, but it doesn't
> look quite right.
>

I can fix both of these and apply. No need to repost.

--
Regards,
Sudeep