firmware: smccc: Support optional Arm SMCCC SOC_ID name

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
Acked-by: Mark Rutland <mark.rutland@arm.com>
Message-Id: <20250219005932.3466-1-paul@os.amperecomputing.com>
(sudeep.holla: Dropped regsize variable and used 8 instead as Mark suggested)
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>

drivers/firmware/smccc/soc_id.c

@@ -32,6 +32,85 @@
 static struct soc_device *soc_dev;
 static struct soc_device_attribute *soc_dev_attr;
 
+#ifdef CONFIG_ARM64
+
+static char __ro_after_init smccc_soc_id_name[136] = "";
+
+static inline void str_fragment_from_reg(char *dst, unsigned long reg)
+{
+	dst[0] = (reg >> 0)  & 0xff;
+	dst[1] = (reg >> 8)  & 0xff;
+	dst[2] = (reg >> 16) & 0xff;
+	dst[3] = (reg >> 24) & 0xff;
+	dst[4] = (reg >> 32) & 0xff;
+	dst[5] = (reg >> 40) & 0xff;
+	dst[6] = (reg >> 48) & 0xff;
+	dst[7] = (reg >> 56) & 0xff;
+}
+
+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) {
+		/*
+		 * 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 + 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 * 2, res.a3);
+		str_fragment_from_reg(smccc_soc_id_name + 8 * 3, res.a4);
+		str_fragment_from_reg(smccc_soc_id_name + 8 * 4, res.a5);
+		str_fragment_from_reg(smccc_soc_id_name + 8 * 5, res.a6);
+		str_fragment_from_reg(smccc_soc_id_name + 8 * 6, res.a7);
+		str_fragment_from_reg(smccc_soc_id_name + 8 * 7, res.a8);
+		str_fragment_from_reg(smccc_soc_id_name + 8 * 8, res.a9);
+		str_fragment_from_reg(smccc_soc_id_name + 8 * 9, res.a10);
+		str_fragment_from_reg(smccc_soc_id_name + 8 * 10, res.a11);
+		str_fragment_from_reg(smccc_soc_id_name + 8 * 11, res.a12);
+		str_fragment_from_reg(smccc_soc_id_name + 8 * 12, res.a13);
+		str_fragment_from_reg(smccc_soc_id_name + 8 * 13, res.a14);
+		str_fragment_from_reg(smccc_soc_id_name + 8 * 14, res.a15);
+		str_fragment_from_reg(smccc_soc_id_name + 8 * 15, res.a16);
+		str_fragment_from_reg(smccc_soc_id_name + 8 * 16, res.a17);
+
+		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");
+			else
+				return smccc_soc_id_name;
+		}
+	}
+
+	return NULL;
+}
+
+#else
+
+static char __init *smccc_soc_name_init(void)
+{
+	return NULL;
+}
+
+#endif
+
 static int __init smccc_soc_init(void)
 {
 	int soc_id_rev, soc_id_version;
@@ -72,6 +151,7 @@ static int __init smccc_soc_init(void)
 	soc_dev_attr->soc_id = soc_id_str;
 	soc_dev_attr->revision = soc_id_rev_str;
 	soc_dev_attr->family = soc_id_jep106_id_str;
+	soc_dev_attr->machine = smccc_soc_name_init();
 
 	soc_dev = soc_device_register(soc_dev_attr);
 	if (IS_ERR(soc_dev)) {

include/linux/arm-smccc.h

@@ -639,5 +639,45 @@ asmlinkage void __arm_smccc_hvc(unsigned long a0, unsigned long a1,
 		method;							\
 	})
 
+#ifdef CONFIG_ARM64
+
+#define __fail_smccc_1_2(___res)					\
+	do {								\
+		if (___res)						\
+			___res->a0 = SMCCC_RET_NOT_SUPPORTED;		\
+	} while (0)
+
+/*
+ * arm_smccc_1_2_invoke() - make an SMCCC v1.2 compliant call
+ *
+ * @args: SMC args are in the a0..a17 fields of the arm_smcc_1_2_regs structure
+ * @res: result values from registers 0 to 17
+ *
+ * This macro will make either an HVC call or an SMC call depending on the
+ * current SMCCC conduit. If no valid conduit is available then -1
+ * (SMCCC_RET_NOT_SUPPORTED) is returned in @res.a0 (if supplied).
+ *
+ * The return value also provides the conduit that was used.
+ */
+#define arm_smccc_1_2_invoke(args, res) ({				\
+		struct arm_smccc_1_2_regs *__args = args;		\
+		struct arm_smccc_1_2_regs *__res = res;			\
+		int method = arm_smccc_1_1_get_conduit();		\
+		switch (method) {					\
+		case SMCCC_CONDUIT_HVC:					\
+			arm_smccc_1_2_hvc(__args, __res);		\
+			break;						\
+		case SMCCC_CONDUIT_SMC:					\
+			arm_smccc_1_2_smc(__args, __res);		\
+			break;						\
+		default:						\
+			__fail_smccc_1_2(__res);			\
+			method = SMCCC_CONDUIT_NONE;			\
+			break;						\
+		}							\
+		method;							\
+	})
+#endif /*CONFIG_ARM64*/
+
 #endif /*__ASSEMBLY__*/
 #endif /*__LINUX_ARM_SMCCC_H*/