linux-kernel - [PATCH v1 1/2] RISC-V: add non-alternative fallback for riscv_has_extension

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Date:   Fri, 24 Mar 2023 10:05:38 +0000
From:   Conor Dooley <conor.dooley@...rochip.com>
To:     <palmer@...belt.com>
CC:     <conor@...nel.org>, <conor.dooley@...rochip.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Heiko Stuebner <heiko.stuebner@...ll.eu>,
        "Andrew Jones" <ajones@...tanamicro.com>,
        Anup Patel <apatel@...tanamicro.com>,
        Jisheng Zhang <jszhang@...nel.org>,
        "Jason A . Donenfeld" <Jason@...c4.com>,
        <linux-riscv@...ts.infradead.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH v1 1/2] RISC-V: add non-alternative fallback for riscv_has_extension_[un]likely()

The has_fpu() check, which in turn calls riscv_has_extension_likely(),
relies on alternatives to figure out whether the system has an FPU.
As a result, it will malfunction on XIP kernels, as they do not support
the alternatives mechanism.

When alternatives support is not present, fall back to using
__riscv_isa_extension_available() in riscv_has_extension_[un]likely()
instead stead, which handily takes the same argument, so that kernels
that do not support alternatives can accurately report the presence of
FPU support.

Fixes: 702e64550b12 ("riscv: fpu: switch has_fpu() to riscv_has_extension_likely()")
Link: https://lore.kernel.org/all/ad445951-3d13-4644-94d9-e0989cda39c3@spud/
Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
---
 arch/riscv/include/asm/hwcap.h | 50 ++++++++++++++++++++--------------
 1 file changed, 30 insertions(+), 20 deletions(-)

diff --git a/arch/riscv/include/asm/hwcap.h b/arch/riscv/include/asm/hwcap.h
index e3021b2590de..6263a0de1c6a 100644
--- a/arch/riscv/include/asm/hwcap.h
+++ b/arch/riscv/include/asm/hwcap.h
@@ -57,18 +57,31 @@ struct riscv_isa_ext_data {
 	unsigned int isa_ext_id;
 };
 
+unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap);
+
+#define riscv_isa_extension_mask(ext) BIT_MASK(RISCV_ISA_EXT_##ext)
+
+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)
+
 static __always_inline bool
 riscv_has_extension_likely(const unsigned long ext)
 {
 	compiletime_assert(ext < RISCV_ISA_EXT_MAX,
 			   "ext must be < RISCV_ISA_EXT_MAX");
 
-	asm_volatile_goto(
-	ALTERNATIVE("j	%l[l_no]", "nop", 0, %[ext], 1)
-	:
-	: [ext] "i" (ext)
-	:
-	: l_no);
+	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
+		asm_volatile_goto(
+		ALTERNATIVE("j	%l[l_no]", "nop", 0, %[ext], 1)
+		:
+		: [ext] "i" (ext)
+		:
+		: l_no);
+	} else {
+		if (!__riscv_isa_extension_available(NULL, ext))
+			goto l_no;
+	}
 
 	return true;
 l_no:
@@ -81,26 +94,23 @@ riscv_has_extension_unlikely(const unsigned long ext)
 	compiletime_assert(ext < RISCV_ISA_EXT_MAX,
 			   "ext must be < RISCV_ISA_EXT_MAX");
 
-	asm_volatile_goto(
-	ALTERNATIVE("nop", "j	%l[l_yes]", 0, %[ext], 1)
-	:
-	: [ext] "i" (ext)
-	:
-	: l_yes);
+	if (IS_ENABLED(CONFIG_RISCV_ALTERNATIVE)) {
+		asm_volatile_goto(
+		ALTERNATIVE("nop", "j	%l[l_yes]", 0, %[ext], 1)
+		:
+		: [ext] "i" (ext)
+		:
+		: l_yes);
+	} else {
+		if (__riscv_isa_extension_available(NULL, ext))
+			goto l_yes;
+	}
 
 	return false;
 l_yes:
 	return true;
 }
 
-unsigned long riscv_isa_extension_base(const unsigned long *isa_bitmap);
-
-#define riscv_isa_extension_mask(ext) BIT_MASK(RISCV_ISA_EXT_##ext)
-
-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)
-
 #endif
 
 #endif /* _ASM_RISCV_HWCAP_H */
-- 
2.39.2