[PATCH v1 1/2] RISC-V: Provide a framework for parsing multi-letter ISA extensions

[Atish Patra <atishp@atishpatra.org>]

Recently, there were 15 specifications/40 ISA extensions were ratified.
Except hypervisor ('H') extension, all of them are multi-letter extensions.
Going forward, there will be more number of multi-letter extensions as
well. Parsing all of these extensions from ISA string is not scalable.
Thus, this patch provides a DT based framework to for easy parsing and
querying of any ISA extensions. It facilitates custom user visible strings
for the ISA extensions via /proc/cpuinfo as well.

Currently, there are no platforms with heterogeneous Linux capable harts.
That's why, this patch supports only a single DT node which can only work
for systems with homogeneous harts. To support heterogeneous systems, this
cpu node must be a subnode for each cpu.

Signed-off-by: Atish Patra <atishp@rivosinc.com>
---
 arch/riscv/include/asm/hwcap.h | 31 ++++++++++++++++++
 arch/riscv/kernel/cpu.c        | 16 ++++++++++
 arch/riscv/kernel/cpufeature.c | 58 +++++++++++++++++++++++++++++++++-
 3 files changed, 104 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index 5ce50468aff1..368ab0f330c8 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -34,7 +34,36 @@ extern unsigned long elf_hwcap;
 #define RISCV_ISA_EXT_s		('s' - 'a')
 #define RISCV_ISA_EXT_u		('u' - 'a')
 
+/*
+ * Increse this to higher value as kernel support more ISA extensions.
+ */
 #define RISCV_ISA_EXT_MAX	64
+#define RISCV_ISA_EXT_NAME_LEN_MAX 32
+/* The base ID for multi-letter ISA extensions */
+#define RISCV_ISA_EXT_BASE 26
+
+/*
+ * This enum represent the logical ID for each multi-letter RISC-V ISA extension.
+ * The logical ID should start from RISCV_ISA_EXT_BASE and must not exceed
+ * RISCV_ISA_EXT_MAX. 0-25 range is reserved for single letter
+ * extensions while all the multi-letter extensions should define the next
+ * available logical extension id.
+ */
+enum riscv_isa_ext_id {
+	RISCV_ISA_EXT_ID_MAX = RISCV_ISA_EXT_MAX,
+};
+
+struct riscv_isa_ext_data {
+	struct list_head node;
+	/* Name of the extension property in DT */
+	char dtprop[RISCV_ISA_EXT_NAME_LEN_MAX];
+	/* Name of the extension displayed to userspace via /proc/cpuinfo */
+	char uprop[RISCV_ISA_EXT_NAME_LEN_MAX];
+	/* The logical ISA extension ID */
+	unsigned int isa_ext_id;
+};
+
+extern struct list_head riscv_isa_ext_list;
 
 unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap);
 
@@ -44,6 +73,8 @@ bool __riscv_isa_extension_available(const unsigned long *isa_bitmap, int bit);
 #define riscv_isa_extension_available(isa_bitmap, ext)	\
 	__riscv_isa_extension_available(isa_bitmap, RISCV_ISA_EXT_##ext)
 
+int riscv_isa_ext_list_add(struct riscv_isa_ext_data *edata);
+
 #endif
 
 #endif /* _ASM_RISCV_HWCAP_H */
diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
index f13b2c9ea912..dad95bdd3cca 100644
--- a/arch/riscv/kernel/cpu.c
+++ b/arch/riscv/kernel/cpu.c
@@ -71,6 +71,21 @@ static void print_isa(struct seq_file *f, const char *isa)
 	seq_puts(f, "\n");
 }
 
+static void print_isa_ext(struct seq_file *f)
+{
+	struct riscv_isa_ext_data *edata;
+	int count = 0;
+
+	seq_puts(f, "isa-ext\t\t: ");
+	list_for_each_entry(edata, &riscv_isa_ext_list, node) {
+		if (count)
+			seq_puts(f, ",");
+		seq_write(f, edata->uprop, strnlen(edata->uprop, RISCV_ISA_EXT_NAME_LEN_MAX));
+		count++;
+	}
+	seq_puts(f, "\n");
+}
+
 static void print_mmu(struct seq_file *f, const char *mmu_type)
 {
 #if defined(CONFIG_32BIT)
@@ -113,6 +128,7 @@ static int c_show(struct seq_file *m, void *v)
 	seq_printf(m, "hart\t\t: %lu\n", cpuid_to_hartid_map(cpu_id));
 	if (!of_property_read_string(node, "riscv,isa", &isa))
 		print_isa(m, isa);
+	print_isa_ext(m);
 	if (!of_property_read_string(node, "mmu-type", &mmu))
 		print_mmu(m, mmu);
 	if (!of_property_read_string(node, "compatible", &compat)
diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index d959d207a40d..c70eeec17f5b 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -7,6 +7,8 @@
  */
 
 #include <linux/bitmap.h>
+#include <linux/list.h>
+#include <linux/slab.h>
 #include <linux/of.h>
 #include <asm/processor.h>
 #include <asm/hwcap.h>
@@ -18,6 +20,8 @@ unsigned long elf_hwcap __read_mostly;
 /* Host ISA bitmap */
 static DECLARE_BITMAP(riscv_isa, RISCV_ISA_EXT_MAX) __read_mostly;
 
+LIST_HEAD(riscv_isa_ext_list);
+
 #ifdef CONFIG_FPU
 __ro_after_init DEFINE_STATIC_KEY_FALSE(cpu_hwcap_fpu);
 #endif
@@ -59,12 +63,60 @@ bool __riscv_isa_extension_available(const unsigned long *isa_bitmap, int bit)
 }
 EXPORT_SYMBOL_GPL(__riscv_isa_extension_available);
 
+#define __RISCV_ISA_EXT_DATA(DTPROP, UPROP, EXTID) \
+	{							\
+		.dtprop = #DTPROP,				\
+		.uprop = #UPROP,				\
+		.isa_ext_id = EXTID,				\
+	}
+
+static struct riscv_isa_ext_data isa_ext_arr[] = {
+	__RISCV_ISA_EXT_DATA("", "", RISCV_ISA_EXT_MAX),
+};
+
+int riscv_isa_ext_list_add(struct riscv_isa_ext_data *edata)
+{
+	struct device_node *node, *enode;
+	int eid;
+
+	if (!edata || !edata->dtprop)
+		return -EINVAL;
+
+	node = of_find_node_by_path("/cpus");
+	if (!node) {
+		pr_err("No CPU information found in DT\n");
+		return -ENOENT;
+	}
+
+	enode = of_get_child_by_name(node, "riscv,isa-ext");
+	if (!enode) {
+		pr_err("No riscv-isa-ext found in DT\n");
+		return -ENOENT;
+	}
+
+	eid = edata->isa_ext_id;
+	if (eid < RISCV_ISA_EXT_BASE || eid >= RISCV_ISA_EXT_MAX)
+		return -EINVAL;
+
+	if (!of_property_read_bool(enode, edata->dtprop)) {
+		pr_err("The ISA extension %s is not present in DT\n", edata->dtprop);
+		return -ENODEV;
+	}
+
+	/* Enable the extension id in the riscv_isa for easier probing */
+	riscv_isa[0] |= 1 << eid;
+	list_add(&edata->node, &riscv_isa_ext_list);
+	pr_info("RISC-V ISA extension '%s' available\n", edata->uprop);
+
+	return 0;
+}
+
 void __init riscv_fill_hwcap(void)
 {
 	struct device_node *node;
 	const char *isa;
 	char print_str[BITS_PER_LONG + 1];
-	size_t i, j, isa_len;
+	size_t i, j, isa_len, ext_arr_sz;
 	static unsigned long isa2hwcap[256] = {0};
 
 	isa2hwcap['i'] = isa2hwcap['I'] = COMPAT_HWCAP_ISA_I;
@@ -148,4 +200,8 @@ void __init riscv_fill_hwcap(void)
 	if (elf_hwcap & (COMPAT_HWCAP_ISA_F | COMPAT_HWCAP_ISA_D))
 		static_branch_enable(&cpu_hwcap_fpu);
 #endif
+
+	ext_arr_sz = ARRAY_SIZE(isa_ext_arr);
+	for (i = 0; i < ext_arr_sz - 1; i++)
+		riscv_isa_ext_list_add(&isa_ext_arr[i]);
 }
-- 
2.33.1


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