linux-kernel - [RFC v1 2/5] RISC-V: add f & d extension validation checks

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Message-ID: <20241002-stuffed-trance-1323386dd80b@spud>
Date: Wed,  2 Oct 2024 17:10:55 +0100
From: Conor Dooley <conor@...nel.org>
To: linux-riscv@...ts.infradead.org
Cc: conor@...nel.org,
	Conor Dooley <conor.dooley@...rochip.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Clément Léger <cleger@...osinc.com>,
	Andy Chiu <andybnac@...il.com>,
	devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [RFC v1 2/5] RISC-V: add f & d extension validation checks

From: Conor Dooley <conor.dooley@...rochip.com>

Using Clement's new validation callbacks, support checking that
dependencies have been satisfied for the floating point extensions.

The check for "d" might be slightly confusingly shorter than that of "f",
despite "d" depending on "f". This is because the requirement that a
hart supporting double precision must also support single precision,
should be validated by dt-bindings etc, not the kernel but lack of
support for single precision only is a limitation of the kernel.

Since vector will now be disabled proactively, there's no need to clear
the bit in elf_hwcap in riscv_fill_hwcap() any longer.

Signed-off-by: Conor Dooley <conor.dooley@...rochip.com>
---
 arch/riscv/kernel/cpufeature.c | 36 +++++++++++++++++++++++-----------
 1 file changed, 25 insertions(+), 11 deletions(-)

diff --git a/arch/riscv/kernel/cpufeature.c b/arch/riscv/kernel/cpufeature.c
index 84a2ad2581cb0..b8a22ee76c2ef 100644
--- a/arch/riscv/kernel/cpufeature.c
+++ b/arch/riscv/kernel/cpufeature.c
@@ -101,6 +101,29 @@ static int riscv_ext_zicboz_validate(const struct riscv_isa_ext_data *data,
 	return 0;
 }
 
+static int riscv_ext_f_validate(const struct riscv_isa_ext_data *data,
+				const unsigned long *isa_bitmap)
+{
+	if (!__riscv_isa_extension_available(isa_bitmap, RISCV_ISA_EXT_d)) {
+		pr_warn_once("This kernel does not support systems with F but not D\n");
+		return -EINVAL;
+	}
+
+	if (IS_ENABLED(CONFIG_FPU))
+		return -EINVAL;
+
+	return 0;
+}
+
+static int riscv_ext_d_validate(const struct riscv_isa_ext_data *data,
+				const unsigned long *isa_bitmap)
+{
+	if (IS_ENABLED(CONFIG_FPU))
+		return -EINVAL;
+
+	return 0;
+}
+
 static int riscv_ext_vector_x_validate(const struct riscv_isa_ext_data *data,
 				     const unsigned long *isa_bitmap)
 {
@@ -351,8 +374,8 @@ 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_VALIDATE(f, RISCV_ISA_EXT_f, riscv_ext_f_validate),
+	__RISCV_ISA_EXT_DATA_VALIDATE(d, RISCV_ISA_EXT_d, riscv_ext_d_validate),
 	__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_VALIDATE(v, RISCV_ISA_EXT_v, riscv_v_exts, riscv_ext_vector_float_validate),
@@ -912,15 +935,6 @@ void __init riscv_fill_hwcap(void)
 		}
 	}
 
-	/*
-	 * We don't support systems with F but without D, so mask those out
-	 * here.
-	 */
-	if ((elf_hwcap & COMPAT_HWCAP_ISA_F) && !(elf_hwcap & COMPAT_HWCAP_ISA_D)) {
-		pr_info("This kernel does not support systems with F but not D\n");
-		elf_hwcap &= ~COMPAT_HWCAP_ISA_F;
-	}
-
 	if (__riscv_isa_extension_available(NULL, RISCV_ISA_EXT_ZVE32X)) {
 		/*
 		 * This cannot fail when called on the boot hart
-- 
2.45.2