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

Paul Benoit
2025-02-19T01:00:02Z

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
---

v3->v4: Address code review identified issues of v3.
v2->v3: Add conditionalization to exclude SOC_ID Name from 32-bit builds.
v1->v2: Address code review identified issues.

drivers/firmware/smccc/soc_id.c | 81 +++++++++++++++++++++++++++++++++
include/linux/arm-smccc.h | 40 ++++++++++++++++
2 files changed, 121 insertions(+)

diff --git a/drivers/firmware/smccc/soc_id.c b/drivers/firmware/smccc/soc_id.c
index 1990263fbba0..7b0688d78dab 100644
--- a/drivers/firmware/smccc/soc_id.c
+++ b/drivers/firmware/smccc/soc_id.c
@@ -32,6 +32,86 @@
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) {
+ 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);
+
+ 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 +152,7 @@ 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)) {
diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
index 67f6fdf2e7cd..eb7eab04755a 100644
--- a/include/linux/arm-smccc.h
+++ b/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*/
--
2.48.1