[PATCH v3 2/2] riscv: accept the atomic extensions this kernel was built with

[Vladimir Kondratiev <vladimir.kondratiev@mobileye.com>]

riscv_early_of_processor_hartid() rejects a hart unless its
riscv,isa-extensions property contains "a". That rejects a Zalrsc-only
hart even when the kernel was built to use only LR/SC.

Require "a" or "zaamo" when the kernel emits AMO, and "a" or "zalrsc"
when it emits LR/SC. A normal build defines both toolchain macros and
still requires the full A extension. The legacy "riscv,isa" fallback
keeps its rv{32,64}ima check.

Signed-off-by: Vladimir Kondratiev <vladimir.kondratiev@mobileye.com>
---
 arch/riscv/kernel/cpu.c | 28 ++++++++++++++++++++++++----
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/arch/riscv/kernel/cpu.c b/arch/riscv/kernel/cpu.c
index 3dbc8cc557dd..5d1e39d16e59 100644
--- a/arch/riscv/kernel/cpu.c
+++ b/arch/riscv/kernel/cpu.c
@@ -82,12 +82,32 @@ int __init riscv_early_of_processor_hartid(struct device_node *node, unsigned lo
 		return -ENODEV;
 
 	if (of_property_match_string(node, "riscv,isa-extensions", "i") < 0 ||
-	    of_property_match_string(node, "riscv,isa-extensions", "m") < 0 ||
-	    of_property_match_string(node, "riscv,isa-extensions", "a") < 0) {
-		pr_warn("CPU with hartid=%lu does not support ima", *hart);
+	    of_property_match_string(node, "riscv,isa-extensions", "m") < 0) {
+		pr_warn("CPU with hartid=%lu does not support im", *hart);
 		return -ENODEV;
 	}
-
+#if !defined(__riscv_atomic) && !defined(__riscv_zaamo) && !defined(__riscv_zalrsc)
+#error "Need AMO or LR/SC atomics"
+#endif
+	/*
+	 * Require each atomic form this kernel emits. The single-letter
+	 * "a" extension satisfies either check. A Zalrsc-only build defines
+	 * __riscv_zalrsc and checks that extension only.
+	 */
+#if defined(__riscv_atomic) || defined(__riscv_zaamo)
+	if (of_property_match_string(node, "riscv,isa-extensions", "a") < 0 &&
+	    of_property_match_string(node, "riscv,isa-extensions", "zaamo") < 0) {
+		pr_warn("CPU with hartid=%lu does not support AMO atomics", *hart);
+		return -ENODEV;
+	}
+#endif
+#if defined(__riscv_atomic) || defined(__riscv_zalrsc)
+	if (of_property_match_string(node, "riscv,isa-extensions", "a") < 0 &&
+	    of_property_match_string(node, "riscv,isa-extensions", "zalrsc") < 0) {
+		pr_warn("CPU with hartid=%lu does not support LR/SC atomics", *hart);
+		return -ENODEV;
+	}
+#endif
 	return 0;
 
 old_interface:

-- 
2.43.0