riscv: Enhance extension probing
Enhance the existing extension probing mechanism by adding support for
more extensions and probing using the "riscv,isa" property. This patch
is ported from the latest upstream linux.
Signed-off-by: Mayuresh Chitale <mchitale@ventanamicro.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
diff --git a/arch/riscv/cpu/cpu.c b/arch/riscv/cpu/cpu.c
index affe700..f3f9f9f 100644
--- a/arch/riscv/cpu/cpu.c
+++ b/arch/riscv/cpu/cpu.c
@@ -14,8 +14,12 @@
#include <log.h>
#include <asm/encoding.h>
#include <asm/system.h>
+#include <asm/hwcap.h>
+#include <asm/cpufeature.h>
#include <dm/uclass-internal.h>
#include <linux/bitops.h>
+#include <linux/log2.h>
+#include <linux/ctype.h>
/*
* The variables here must be stored in the data section since they are used
@@ -33,6 +37,559 @@
#endif
#endif
+/* Host ISA bitmap */
+static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __section(".data");
+
+static unsigned int riscv_cbom_block_size __section(".data");
+static unsigned int riscv_cboz_block_size __section(".data");
+/**
+ * __riscv_isa_extension_available() - Check whether given extension
+ * is available or not
+ *
+ * @bit: bit position of the desired extension
+ * Return: true or false
+ *
+ */
+static bool __riscv_isa_extension_available(unsigned int bit)
+{
+ if (bit >= RISCV_ISA_EXT_MAX)
+ return false;
+
+ return test_bit(bit, riscv_isa) ? true : false;
+}
+
+inline unsigned int riscv_get_cbom_block_size(void)
+{
+ return riscv_cbom_block_size;
+}
+
+inline unsigned int riscv_get_cboz_block_size(void)
+{
+ return riscv_cboz_block_size;
+}
+
+static int riscv_ext_zicbom_validate(const struct riscv_isa_ext_data *data,
+ const unsigned long *isa_bitmap)
+{
+ struct udevice *dev;
+
+ if (!CONFIG_IS_ENABLED(RISCV_ISA_ZICBOM) || riscv_cbom_block_size)
+ return 0;
+
+ uclass_first_device(UCLASS_CPU, &dev);
+ if (!dev) {
+ log_info("Failed to get cpu device!\n");
+ return -ENXIO;
+ }
+
+ if (!dev_read_u32(dev, "riscv,cbom-block-size",
+ &riscv_cbom_block_size)) {
+ if (!riscv_cbom_block_size) {
+ log_err("Zicbom detected in ISA string, disabling as no cbom-block-size found\n");
+ return -EINVAL;
+ }
+ if (!is_power_of_2(riscv_cbom_block_size)) {
+ log_err("Zicbom disabled as cbom-block-size present, but is not a power-of-2\n");
+ return -EINVAL;
+ }
+ return 0;
+ } else {
+ return -EINVAL;
+ }
+}
+
+static int riscv_ext_zicboz_validate(const struct riscv_isa_ext_data *data,
+ const unsigned long *isa_bitmap)
+{
+ struct udevice *dev;
+
+ if (!CONFIG_IS_ENABLED(RISCV_ISA_ZICBOM) || riscv_cboz_block_size)
+ return 0;
+
+ uclass_first_device(UCLASS_CPU, &dev);
+ if (!dev) {
+ log_debug("Failed to get cpu device!\n");
+ return -ENXIO;
+ }
+
+ if (!dev_read_u32(dev, "riscv,cboz-block-size",
+ &riscv_cboz_block_size)) {
+ if (!riscv_cboz_block_size) {
+ log_err("Zicboz detected in ISA string, disabling as no cboz-block-size found\n");
+ return -EINVAL;
+ }
+ if (!is_power_of_2(riscv_cboz_block_size)) {
+ log_err("Zicboz disabled as cboz-block-size present, but is not a power-of-2\n");
+ return -EINVAL;
+ }
+ return 0;
+ } else {
+ return -EINVAL;
+ }
+}
+
+static int riscv_ext_zca_depends(const struct riscv_isa_ext_data *data,
+ const unsigned long *isa_bitmap)
+{
+ if (__riscv_isa_extension_available(RISCV_ISA_EXT_ZCA))
+ return 0;
+
+ return -EINVAL;
+}
+
+static int riscv_ext_zcd_validate(const struct riscv_isa_ext_data *data,
+ const unsigned long *isa_bitmap)
+{
+ if (__riscv_isa_extension_available(RISCV_ISA_EXT_ZCA) &&
+ __riscv_isa_extension_available(RISCV_ISA_EXT_d))
+ return 0;
+
+ return -EINVAL;
+}
+
+static int riscv_ext_zcf_validate(const struct riscv_isa_ext_data *data,
+ const unsigned long *isa_bitmap)
+{
+ if (IS_ENABLED(CONFIG_64BIT))
+ return -EINVAL;
+
+ if (__riscv_isa_extension_available(RISCV_ISA_EXT_ZCA) &&
+ __riscv_isa_extension_available(RISCV_ISA_EXT_f))
+ return 0;
+
+ return -EINVAL;
+}
+
+static const unsigned int riscv_zk_bundled_exts[] = {
+ RISCV_ISA_EXT_ZBKB,
+ RISCV_ISA_EXT_ZBKC,
+ RISCV_ISA_EXT_ZBKX,
+ RISCV_ISA_EXT_ZKND,
+ RISCV_ISA_EXT_ZKNE,
+ RISCV_ISA_EXT_ZKR,
+ RISCV_ISA_EXT_ZKT,
+};
+
+static const unsigned int riscv_zkn_bundled_exts[] = {
+ RISCV_ISA_EXT_ZBKB,
+ RISCV_ISA_EXT_ZBKC,
+ RISCV_ISA_EXT_ZBKX,
+ RISCV_ISA_EXT_ZKND,
+ RISCV_ISA_EXT_ZKNE,
+ RISCV_ISA_EXT_ZKNH,
+};
+
+static const unsigned int riscv_zks_bundled_exts[] = {
+ RISCV_ISA_EXT_ZBKB,
+ RISCV_ISA_EXT_ZBKC,
+ RISCV_ISA_EXT_ZKSED,
+ RISCV_ISA_EXT_ZKSH
+};
+
+#define RISCV_ISA_EXT_ZVKN \
+ RISCV_ISA_EXT_ZVKNED, \
+ RISCV_ISA_EXT_ZVKNHB, \
+ RISCV_ISA_EXT_ZVKB, \
+ RISCV_ISA_EXT_ZVKT
+
+static const unsigned int riscv_zvkn_bundled_exts[] = {
+ RISCV_ISA_EXT_ZVKN
+};
+
+static const unsigned int riscv_zvknc_bundled_exts[] = {
+ RISCV_ISA_EXT_ZVKN,
+ RISCV_ISA_EXT_ZVBC
+};
+
+static const unsigned int riscv_zvkng_bundled_exts[] = {
+ RISCV_ISA_EXT_ZVKN,
+ RISCV_ISA_EXT_ZVKG
+};
+
+#define RISCV_ISA_EXT_ZVKS \
+ RISCV_ISA_EXT_ZVKSED, \
+ RISCV_ISA_EXT_ZVKSH, \
+ RISCV_ISA_EXT_ZVKB, \
+ RISCV_ISA_EXT_ZVKT
+
+static const unsigned int riscv_zvks_bundled_exts[] = {
+ RISCV_ISA_EXT_ZVKS
+};
+
+static const unsigned int riscv_zvksc_bundled_exts[] = {
+ RISCV_ISA_EXT_ZVKS,
+ RISCV_ISA_EXT_ZVBC
+};
+
+static const unsigned int riscv_zvksg_bundled_exts[] = {
+ RISCV_ISA_EXT_ZVKS,
+ RISCV_ISA_EXT_ZVKG
+};
+
+static const unsigned int riscv_zvbb_exts[] = {
+ RISCV_ISA_EXT_ZVKB
+};
+
+#define RISCV_ISA_EXT_ZVE64F_IMPLY_LIST \
+ RISCV_ISA_EXT_ZVE64X, \
+ RISCV_ISA_EXT_ZVE32F, \
+ RISCV_ISA_EXT_ZVE32X
+
+#define RISCV_ISA_EXT_ZVE64D_IMPLY_LIST \
+ RISCV_ISA_EXT_ZVE64F, \
+ RISCV_ISA_EXT_ZVE64F_IMPLY_LIST
+
+#define RISCV_ISA_EXT_V_IMPLY_LIST \
+ RISCV_ISA_EXT_ZVE64D, \
+ RISCV_ISA_EXT_ZVE64D_IMPLY_LIST
+
+static const unsigned int riscv_zve32f_exts[] = {
+ RISCV_ISA_EXT_ZVE32X
+};
+
+static const unsigned int riscv_zve64f_exts[] = {
+ RISCV_ISA_EXT_ZVE64F_IMPLY_LIST
+};
+
+static const unsigned int riscv_zve64d_exts[] = {
+ RISCV_ISA_EXT_ZVE64D_IMPLY_LIST
+};
+
+static const unsigned int riscv_v_exts[] = {
+ RISCV_ISA_EXT_V_IMPLY_LIST
+};
+
+static const unsigned int riscv_zve64x_exts[] = {
+ RISCV_ISA_EXT_ZVE32X,
+ RISCV_ISA_EXT_ZVE64X
+};
+
+/*
+ * While the [ms]envcfg CSRs were not defined until version 1.12 of the RISC-V
+ * privileged ISA, the existence of the CSRs is implied by any extension which
+ * specifies [ms]envcfg bit(s). Hence, we define a custom ISA extension for the
+ * existence of the CSR, and treat it as a subset of those other extensions.
+ */
+static const unsigned int riscv_xlinuxenvcfg_exts[] = {
+ RISCV_ISA_EXT_XLINUXENVCFG
+};
+
+/*
+ * Zc* spec states that:
+ * - C always implies Zca
+ * - C+F implies Zcf (RV32 only)
+ * - C+D implies Zcd
+ *
+ * These extensions will be enabled and then validated depending on the
+ * availability of F/D RV32.
+ */
+static const unsigned int riscv_c_exts[] = {
+ RISCV_ISA_EXT_ZCA,
+ RISCV_ISA_EXT_ZCF,
+ RISCV_ISA_EXT_ZCD,
+};
+
+/*
+ * The canonical order of ISA extension names in the ISA string is defined in
+ * chapter 27 of the unprivileged specification.
+ *
+ * Ordinarily, for in-kernel data structures, this order is unimportant but
+ * isa_ext_arr defines the order of the ISA string in /proc/cpuinfo.
+ *
+ * The specification uses vague wording, such as should, when it comes to
+ * ordering, so for our purposes the following rules apply:
+ *
+ * 1. All multi-letter extensions must be separated from other extensions by an
+ * underscore.
+ *
+ * 2. Additional standard extensions (starting with 'Z') must be sorted after
+ * single-letter extensions and before any higher-privileged extensions.
+ *
+ * 3. The first letter following the 'Z' conventionally indicates the most
+ * closely related alphabetical extension category, IMAFDQLCBKJTPVH.
+ * If multiple 'Z' extensions are named, they must be ordered first by
+ * category, then alphabetically within a category.
+ *
+ * 3. Standard supervisor-level extensions (starting with 'S') must be listed
+ * after standard unprivileged extensions. If multiple supervisor-level
+ * extensions are listed, they must be ordered alphabetically.
+ *
+ * 4. Standard machine-level extensions (starting with 'Zxm') must be listed
+ * after any lower-privileged, standard extensions. If multiple
+ * machine-level extensions are listed, they must be ordered
+ * alphabetically.
+ *
+ * 5. Non-standard extensions (starting with 'X') must be listed after all
+ * standard extensions. If multiple non-standard extensions are listed, they
+ * must be ordered alphabetically.
+ *
+ * An example string following the order is:
+ * rv64imadc_zifoo_zigoo_zafoo_sbar_scar_zxmbaz_xqux_xrux
+ *
+ * New entries to this struct should follow the ordering rules described above.
+ */
+const struct riscv_isa_ext_data riscv_isa_ext[] = {
+ __RISCV_ISA_EXT_DATA(i, RISCV_ISA_EXT_i),
+ __RISCV_ISA_EXT_DATA(m, RISCV_ISA_EXT_m),
+ __RISCV_ISA_EXT_DATA(a, RISCV_ISA_EXT_a),
+ __RISCV_ISA_EXT_DATA(f, RISCV_ISA_EXT_f),
+ __RISCV_ISA_EXT_DATA(d, RISCV_ISA_EXT_d),
+ __RISCV_ISA_EXT_DATA(q, RISCV_ISA_EXT_q),
+ __RISCV_ISA_EXT_SUPERSET(c, RISCV_ISA_EXT_c, riscv_c_exts),
+ __RISCV_ISA_EXT_SUPERSET(v, RISCV_ISA_EXT_v, riscv_v_exts),
+ __RISCV_ISA_EXT_DATA(h, RISCV_ISA_EXT_h),
+ __RISCV_ISA_EXT_SUPERSET_VALIDATE(zicbom, RISCV_ISA_EXT_ZICBOM, riscv_xlinuxenvcfg_exts,
+ riscv_ext_zicbom_validate),
+ __RISCV_ISA_EXT_SUPERSET_VALIDATE(zicboz, RISCV_ISA_EXT_ZICBOZ, riscv_xlinuxenvcfg_exts,
+ riscv_ext_zicboz_validate),
+ __RISCV_ISA_EXT_DATA(zicntr, RISCV_ISA_EXT_ZICNTR),
+ __RISCV_ISA_EXT_DATA(zicond, RISCV_ISA_EXT_ZICOND),
+ __RISCV_ISA_EXT_DATA(zicsr, RISCV_ISA_EXT_ZICSR),
+ __RISCV_ISA_EXT_DATA(zifencei, RISCV_ISA_EXT_ZIFENCEI),
+ __RISCV_ISA_EXT_DATA(zihintntl, RISCV_ISA_EXT_ZIHINTNTL),
+ __RISCV_ISA_EXT_DATA(zihintpause, RISCV_ISA_EXT_ZIHINTPAUSE),
+ __RISCV_ISA_EXT_DATA(zihpm, RISCV_ISA_EXT_ZIHPM),
+ __RISCV_ISA_EXT_DATA(zimop, RISCV_ISA_EXT_ZIMOP),
+ __RISCV_ISA_EXT_DATA(zacas, RISCV_ISA_EXT_ZACAS),
+ __RISCV_ISA_EXT_DATA(zawrs, RISCV_ISA_EXT_ZAWRS),
+ __RISCV_ISA_EXT_DATA(zfa, RISCV_ISA_EXT_ZFA),
+ __RISCV_ISA_EXT_DATA(zfh, RISCV_ISA_EXT_ZFH),
+ __RISCV_ISA_EXT_DATA(zfhmin, RISCV_ISA_EXT_ZFHMIN),
+ __RISCV_ISA_EXT_DATA(zca, RISCV_ISA_EXT_ZCA),
+ __RISCV_ISA_EXT_DATA_VALIDATE(zcb, RISCV_ISA_EXT_ZCB, riscv_ext_zca_depends),
+ __RISCV_ISA_EXT_DATA_VALIDATE(zcd, RISCV_ISA_EXT_ZCD, riscv_ext_zcd_validate),
+ __RISCV_ISA_EXT_DATA_VALIDATE(zcf, RISCV_ISA_EXT_ZCF, riscv_ext_zcf_validate),
+ __RISCV_ISA_EXT_DATA_VALIDATE(zcmop, RISCV_ISA_EXT_ZCMOP, riscv_ext_zca_depends),
+ __RISCV_ISA_EXT_DATA(zba, RISCV_ISA_EXT_ZBA),
+ __RISCV_ISA_EXT_DATA(zbb, RISCV_ISA_EXT_ZBB),
+ __RISCV_ISA_EXT_DATA(zbc, RISCV_ISA_EXT_ZBC),
+ __RISCV_ISA_EXT_DATA(zbkb, RISCV_ISA_EXT_ZBKB),
+ __RISCV_ISA_EXT_DATA(zbkc, RISCV_ISA_EXT_ZBKC),
+ __RISCV_ISA_EXT_DATA(zbkx, RISCV_ISA_EXT_ZBKX),
+ __RISCV_ISA_EXT_DATA(zbs, RISCV_ISA_EXT_ZBS),
+ __RISCV_ISA_EXT_BUNDLE(zk, riscv_zk_bundled_exts),
+ __RISCV_ISA_EXT_BUNDLE(zkn, riscv_zkn_bundled_exts),
+ __RISCV_ISA_EXT_DATA(zknd, RISCV_ISA_EXT_ZKND),
+ __RISCV_ISA_EXT_DATA(zkne, RISCV_ISA_EXT_ZKNE),
+ __RISCV_ISA_EXT_DATA(zknh, RISCV_ISA_EXT_ZKNH),
+ __RISCV_ISA_EXT_DATA(zkr, RISCV_ISA_EXT_ZKR),
+ __RISCV_ISA_EXT_BUNDLE(zks, riscv_zks_bundled_exts),
+ __RISCV_ISA_EXT_DATA(zkt, RISCV_ISA_EXT_ZKT),
+ __RISCV_ISA_EXT_DATA(zksed, RISCV_ISA_EXT_ZKSED),
+ __RISCV_ISA_EXT_DATA(zksh, RISCV_ISA_EXT_ZKSH),
+ __RISCV_ISA_EXT_DATA(ztso, RISCV_ISA_EXT_ZTSO),
+ __RISCV_ISA_EXT_SUPERSET(zvbb, RISCV_ISA_EXT_ZVBB, riscv_zvbb_exts),
+ __RISCV_ISA_EXT_DATA(zvbc, RISCV_ISA_EXT_ZVBC),
+ __RISCV_ISA_EXT_SUPERSET(zve32f, RISCV_ISA_EXT_ZVE32F, riscv_zve32f_exts),
+ __RISCV_ISA_EXT_DATA(zve32x, RISCV_ISA_EXT_ZVE32X),
+ __RISCV_ISA_EXT_SUPERSET(zve64d, RISCV_ISA_EXT_ZVE64D, riscv_zve64d_exts),
+ __RISCV_ISA_EXT_SUPERSET(zve64f, RISCV_ISA_EXT_ZVE64F, riscv_zve64f_exts),
+ __RISCV_ISA_EXT_SUPERSET(zve64x, RISCV_ISA_EXT_ZVE64X, riscv_zve64x_exts),
+ __RISCV_ISA_EXT_DATA(zvfh, RISCV_ISA_EXT_ZVFH),
+ __RISCV_ISA_EXT_DATA(zvfhmin, RISCV_ISA_EXT_ZVFHMIN),
+ __RISCV_ISA_EXT_DATA(zvkb, RISCV_ISA_EXT_ZVKB),
+ __RISCV_ISA_EXT_DATA(zvkg, RISCV_ISA_EXT_ZVKG),
+ __RISCV_ISA_EXT_BUNDLE(zvkn, riscv_zvkn_bundled_exts),
+ __RISCV_ISA_EXT_BUNDLE(zvknc, riscv_zvknc_bundled_exts),
+ __RISCV_ISA_EXT_DATA(zvkned, RISCV_ISA_EXT_ZVKNED),
+ __RISCV_ISA_EXT_BUNDLE(zvkng, riscv_zvkng_bundled_exts),
+ __RISCV_ISA_EXT_DATA(zvknha, RISCV_ISA_EXT_ZVKNHA),
+ __RISCV_ISA_EXT_DATA(zvknhb, RISCV_ISA_EXT_ZVKNHB),
+ __RISCV_ISA_EXT_BUNDLE(zvks, riscv_zvks_bundled_exts),
+ __RISCV_ISA_EXT_BUNDLE(zvksc, riscv_zvksc_bundled_exts),
+ __RISCV_ISA_EXT_DATA(zvksed, RISCV_ISA_EXT_ZVKSED),
+ __RISCV_ISA_EXT_DATA(zvksh, RISCV_ISA_EXT_ZVKSH),
+ __RISCV_ISA_EXT_BUNDLE(zvksg, riscv_zvksg_bundled_exts),
+ __RISCV_ISA_EXT_DATA(zvkt, RISCV_ISA_EXT_ZVKT),
+ __RISCV_ISA_EXT_DATA(smaia, RISCV_ISA_EXT_SMAIA),
+ __RISCV_ISA_EXT_DATA(smmpm, RISCV_ISA_EXT_SMMPM),
+ __RISCV_ISA_EXT_SUPERSET(smnpm, RISCV_ISA_EXT_SMNPM, riscv_xlinuxenvcfg_exts),
+ __RISCV_ISA_EXT_DATA(smstateen, RISCV_ISA_EXT_SMSTATEEN),
+ __RISCV_ISA_EXT_DATA(ssaia, RISCV_ISA_EXT_SSAIA),
+ __RISCV_ISA_EXT_DATA(sscofpmf, RISCV_ISA_EXT_SSCOFPMF),
+ __RISCV_ISA_EXT_SUPERSET(ssnpm, RISCV_ISA_EXT_SSNPM, riscv_xlinuxenvcfg_exts),
+ __RISCV_ISA_EXT_DATA(sstc, RISCV_ISA_EXT_SSTC),
+ __RISCV_ISA_EXT_DATA(svinval, RISCV_ISA_EXT_SVINVAL),
+ __RISCV_ISA_EXT_DATA(svnapot, RISCV_ISA_EXT_SVNAPOT),
+ __RISCV_ISA_EXT_DATA(svpbmt, RISCV_ISA_EXT_SVPBMT),
+ __RISCV_ISA_EXT_DATA(svvptc, RISCV_ISA_EXT_SVVPTC),
+};
+
+const size_t riscv_isa_ext_count = ARRAY_SIZE(riscv_isa_ext);
+
+static void riscv_isa_set_ext(const struct riscv_isa_ext_data *ext, unsigned long *bitmap)
+{
+ if (ext->id != RISCV_ISA_EXT_INVALID)
+ __set_bit(ext->id, bitmap);
+
+ for (int i = 0; i < ext->subset_ext_size; i++) {
+ if (ext->subset_ext_ids[i] != RISCV_ISA_EXT_INVALID)
+ __set_bit(ext->subset_ext_ids[i], bitmap);
+ }
+}
+
+static void match_isa_ext(const char *name, const char *name_end)
+{
+ for (int i = 0; i < riscv_isa_ext_count; i++) {
+ const struct riscv_isa_ext_data *ext = &riscv_isa_ext[i];
+
+ if ((name_end - name == strlen(ext->name)) &&
+ !strncasecmp(name, ext->name, name_end - name)) {
+ if (ext->validate && !ext->validate(ext, riscv_isa))
+ riscv_isa_set_ext(ext, riscv_isa);
+ break;
+ }
+ }
+}
+
+static void riscv_parse_isa_string(const char *isa)
+{
+ /*
+ * For all possible cpus, we have already validated in
+ * the boot process that they at least contain "rv" and
+ * whichever of "32"/"64" this kernel supports, and so this
+ * section can be skipped.
+ */
+ isa += 4;
+
+ while (*isa) {
+ const char *ext = isa++;
+ const char *ext_end = isa;
+ bool ext_err = false;
+
+ switch (*ext) {
+ case 'x':
+ case 'X':
+ log_warning("Vendor extensions are ignored in riscv,isa. Use riscv,isa-extensions instead.");
+ /*
+ * To skip an extension, we find its end.
+ * As multi-letter extensions must be split from other multi-letter
+ * extensions with an "_", the end of a multi-letter extension will
+ * either be the null character or the "_" at the start of the next
+ * multi-letter extension.
+ */
+ for (; *isa && *isa != '_'; ++isa)
+ ;
+ ext_err = true;
+ break;
+ case 's':
+ /*
+ * Workaround for invalid single-letter 's' & 'u' (QEMU).
+ * No need to set the bit in riscv_isa as 's' & 'u' are
+ * not valid ISA extensions. It works unless the first
+ * multi-letter extension in the ISA string begins with
+ * "Su" and is not prefixed with an underscore.
+ */
+ if (ext[-1] != '_' && ext[1] == 'u') {
+ ++isa;
+ ext_err = true;
+ break;
+ }
+ fallthrough;
+ case 'S':
+ case 'z':
+ case 'Z':
+ /*
+ * Before attempting to parse the extension itself, we find its end.
+ * As multi-letter extensions must be split from other multi-letter
+ * extensions with an "_", the end of a multi-letter extension will
+ * either be the null character or the "_" at the start of the next
+ * multi-letter extension.
+ *
+ * Next, as the extensions version is currently ignored, we
+ * eliminate that portion. This is done by parsing backwards from
+ * the end of the extension, removing any numbers. This may be a
+ * major or minor number however, so the process is repeated if a
+ * minor number was found.
+ *
+ * ext_end is intended to represent the first character *after* the
+ * name portion of an extension, but will be decremented to the last
+ * character itself while eliminating the extensions version number.
+ * A simple re-increment solves this problem.
+ */
+ for (; *isa && *isa != '_'; ++isa)
+ if (unlikely(!isalnum(*isa)))
+ ext_err = true;
+
+ ext_end = isa;
+ if (unlikely(ext_err))
+ break;
+
+ if (!isdigit(ext_end[-1]))
+ break;
+
+ while (isdigit(*--ext_end))
+ ;
+
+ if (tolower(ext_end[0]) != 'p' || !isdigit(ext_end[-1])) {
+ ++ext_end;
+ break;
+ }
+
+ while (isdigit(*--ext_end))
+ ;
+
+ ++ext_end;
+ break;
+ default:
+ /*
+ * Things are a little easier for single-letter extensions, as they
+ * are parsed forwards.
+ *
+ * After checking that our starting position is valid, we need to
+ * ensure that, when isa was incremented at the start of the loop,
+ * that it arrived at the start of the next extension.
+ *
+ * If we are already on a non-digit, there is nothing to do. Either
+ * we have a multi-letter extension's _, or the start of an
+ * extension.
+ *
+ * Otherwise we have found the current extension's major version
+ * number. Parse past it, and a subsequent p/minor version number
+ * if present. The `p` extension must not appear immediately after
+ * a number, so there is no fear of missing it.
+ *
+ */
+ if (unlikely(!isalpha(*ext))) {
+ ext_err = true;
+ break;
+ }
+
+ if (!isdigit(*isa))
+ break;
+
+ while (isdigit(*++isa))
+ ;
+
+ if (tolower(*isa) != 'p')
+ break;
+
+ if (!isdigit(*++isa)) {
+ --isa;
+ break;
+ }
+
+ while (isdigit(*++isa))
+ ;
+
+ break;
+ }
+
+ /*
+ * The parser expects that at the start of an iteration isa points to the
+ * first character of the next extension. As we stop parsing an extension
+ * on meeting a non-alphanumeric character, an extra increment is needed
+ * where the succeeding extension is a multi-letter prefixed with an "_".
+ */
+ if (*isa == '_')
+ ++isa;
+
+ if (unlikely(ext_err))
+ continue;
+ match_isa_ext(ext, ext_end);
+ }
+}
+
static inline bool supports_extension(char ext)
{
#if CONFIG_IS_ENABLED(RISCV_MMODE)