linux-kernel - [PATCH 1/2] RISC-V: sbi: turn sbi

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Message-ID: <20250612145754.2126147-3-rkrcmar@ventanamicro.com>
Date: Thu, 12 Jun 2025 16:57:54 +0200
From: Radim Krčmář <rkrcmar@...tanamicro.com>
To: linux-riscv@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Alexandre Ghiti <alex@...ti.fr>,
	Atish Patra <atishp@...osinc.com>,
	Andrew Jones <ajones@...tanamicro.com>,
	Clément Léger <cleger@...osinc.com>,
	Anup Patel <apatel@...tanamicro.com>
Subject: [PATCH 1/2] RISC-V: sbi: turn sbi_ecall into variadic macro

Counting the arguments to sbi_ecall() and padding with zeros gets old
pretty quick.  It's also harder to distinguish a tailing 0 argument and
the padding.  The patch changes sbi_ecall() to accept anything between 1
and 8 integer arguments.

Those who can count are also given sbi_ecall1() to sbi_ecall8(), which
the variadic magic uses under the hood.  The error messages upon a
programmer error are a bit hairy, as expected of macros, and the
static_assert is there to improve them a bit.

The final goal would be avoid clobbering registers that are not used in
the ecall, but we first have to fix the code generation around
tracepoints if sbi_ecall is expected to be used in paths where
performance is critical.

Signed-off-by: Radim Krčmář <rkrcmar@...tanamicro.com>
---
 arch/riscv/include/asm/sbi.h | 34 +++++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 341e74238aa0..c62db61bd018 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -10,6 +10,7 @@
 #include <linux/types.h>
 #include <linux/cpumask.h>
 #include <linux/jump_label.h>
+#include <linux/build_bug.h>
 
 #ifdef CONFIG_RISCV_SBI
 enum sbi_ext_id {
@@ -465,9 +466,40 @@ struct sbiret __sbi_ecall(unsigned long arg0, unsigned long arg1,
 			  unsigned long arg2, unsigned long arg3,
 			  unsigned long arg4, unsigned long arg5,
 			  int fid, int ext);
-#define sbi_ecall(e, f, a0, a1, a2, a3, a4, a5)	\
+
+#define sbi_ecall1(e) \
+		__sbi_ecall(0, 0, 0, 0, 0, 0, 0, e)
+#define sbi_ecall2(e, f) \
+		__sbi_ecall(0, 0, 0, 0, 0, 0, f, e)
+#define sbi_ecall3(e, f, a0) \
+		__sbi_ecall(a0, 0, 0, 0, 0, 0, f, e)
+#define sbi_ecall4(e, f, a0, a1) \
+		__sbi_ecall(a0, a1, 0, 0, 0, 0, f, e)
+#define sbi_ecall5(e, f, a0, a1, a2) \
+		__sbi_ecall(a0, a1, a2, 0, 0, 0, f, e)
+#define sbi_ecall6(e, f, a0, a1, a2, a3) \
+		__sbi_ecall(a0, a1, a2, a3, 0, 0, f, e)
+#define sbi_ecall7(e, f, a0, a1, a2, a3, a4) \
+		__sbi_ecall(a0, a1, a2, a3, a4, 0, f, e)
+#define sbi_ecall8(e, f, a0, a1, a2, a3, a4, a5) \
 		__sbi_ecall(a0, a1, a2, a3, a4, a5, f, e)
 
+#define __sbi_count_args_magic(_, a, b, c, d, e, f, g, h, N, ...) N
+#define __sbi_count_args(...) \
+	__sbi_count_args_magic(_, ## __VA_ARGS__, 8, 7, 6, 5, 4, 3, 2, 1, 0)
+#define __sbi_count_args2(...) \
+	(sizeof((unsigned long[]){0, ## __VA_ARGS__}) / sizeof(unsigned long) - 1)
+#define __sbi_concat_expanded(a, b) a ## b
+#define __sbi_concat(n) __sbi_concat_expanded(sbi_ecall, n)
+
+/* sbi_ecall selects the appropriate sbi_ecall1 to sbi_ecall8 */
+#define sbi_ecall(...)  \
+	({ \
+		static_assert(__sbi_count_args2(__VA_ARGS__) <= 8); \
+		__sbi_concat(__sbi_count_args(__VA_ARGS__)) \
+				(__VA_ARGS__); \
+	})
+
 #ifdef CONFIG_RISCV_SBI_V01
 void sbi_console_putchar(int ch);
 int sbi_console_getchar(void);
-- 
2.49.0