riscv: add cpufeature handling via alternatives

Some cpufeatures should be handled via the alternatives mechanism to not incur penalties on unsupporting variants. So add a mechanism to handle these similar to cpu erratas. Signed-off-by: Heiko Stuebner <heiko@sntech.de>
c-sky · Jan 18, 2022 · 414a3c26e45780d9f957d3721666dfe099b8643c · 414a3c2
1 parent e28ce4c
commit 414a3c26e45780d9f957d3721666dfe099b8643c
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Showing 4 changed files with 60 additions and 1 deletion.
diff --git a/arch/riscv/include/asm/alternative.h b/arch/riscv/include/asm/alternative.h
@@ -39,5 +39,8 @@ struct errata_checkfunc_id {
 void sifive_errata_patch_func(struct alt_entry *begin, struct alt_entry *end,
 			      unsigned long archid, unsigned long impid,
 			      unsigned int stage);
+
+void riscv_cpufeature_patch_func(struct alt_entry *begin, struct alt_entry *end,
+				 unsigned int stage);
 #endif
 #endif
diff --git a/arch/riscv/include/asm/errata_list.h b/arch/riscv/include/asm/errata_list.h
@@ -14,6 +14,8 @@
 #define	ERRATA_SIFIVE_NUMBER 2
 #endif
 
+#define	CPUFEATURE_NUMBER 0
+
 #ifdef __ASSEMBLY__
 
 #define ALT_INSN_FAULT(x)						\

diff --git a/arch/riscv/kernel/alternative.c b/arch/riscv/kernel/alternative.c
@@ -63,6 +63,8 @@ static void __init_or_module _apply_alternatives(struct alt_entry *begin,
 						 struct alt_entry *end,
 						 unsigned int stage)
 {
+	riscv_cpufeature_patch_func(begin, end, stage);
+
 	if (!vendor_patch_func)
 		return;
 

diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
@@ -8,8 +8,12 @@
 
 #include <linux/bitmap.h>
 #include <linux/of.h>
-#include <asm/processor.h>
+#include <asm/alternative.h>
+#include <asm/errata_list.h>
 #include <asm/hwcap.h>
+#include <asm/patch.h>
+#include <asm/pgtable.h>
+#include <asm/processor.h>
 #include <asm/smp.h>
 #include <asm/switch_to.h>
 
@@ -149,3 +153,51 @@ void __init riscv_fill_hwcap(void)
 		static_branch_enable(&cpu_hwcap_fpu);
 #endif
 }
+
+struct cpufeature_info {
+	char name[ERRATA_STRING_LENGTH_MAX];
+	bool (*check_func)(unsigned int stage);
+};
+
+static const struct cpufeature_info cpufeature_list[CPUFEATURE_NUMBER] = {
+};
+
+static u32 __init cpufeature_probe(unsigned int stage)
+{
+	const struct cpufeature_info *info;
+	u32 cpu_req_feature = 0;
+	int idx;
+
+	for (idx = 0; idx < CPUFEATURE_NUMBER; idx++) {
+		info = &cpufeature_list[idx];
+
+		if (info->check_func(stage))
+			cpu_req_feature |= (1U << idx);
+	}
+
+	return cpu_req_feature;
+}
+
+void riscv_cpufeature_patch_func(struct alt_entry *begin, struct alt_entry *end,
+				 unsigned int stage)
+{
+	u32 cpu_req_feature = cpufeature_probe(stage);
+	u32 cpu_apply_feature = 0;
+	struct alt_entry *alt;
+	u32 tmp;
+
+	for (alt = begin; alt < end; alt++) {
+		if (alt->vendor_id != 0)
+			continue;
+		if (alt->errata_id >= CPUFEATURE_NUMBER) {
+			WARN(1, "This feature id:%d is not in kernel cpufeature list", alt->errata_id);
+			continue;
+		}
+
+		tmp = (1U << alt->errata_id);
+		if (cpu_req_feature & tmp) {
+			patch_text_nosync(alt->old_ptr, alt->alt_ptr, alt->alt_len);
+			cpu_apply_feature |= tmp;
+		}
+	}
+}