Re: [PATCH v8 05/22] RISC-V: Define indirect CSR access helpers

[Paul Walmsley <pjw@kernel.org>]

On Wed, 1 Jul 2026, Atish Patra wrote:

> From: Atish Patra <atishp@rivosinc.com>
> 
> The indirect CSR requires multiple instructions to read/write CSR.
> Add a few helper functions for ease of usage.
> 
> Signed-off-by: Atish Patra <atishp@rivosinc.com>

Thanks.  These macros seem better implemented as static inline functions.  
That also nicely aligns the code with what you write in the patch 
description.

Also, I renamed this file to change the abbreviation "ind" to "indirect", 
along the lines of this feedback here:

   https://lore.kernel.org/linux-riscv/CAHk-=whhSLGZAx3N5jJpb4GLFDqH_QvS07D+6BnkPWmCEzTAgw@mail.gmail.com/

This case is even worse since there are already uses of "csr_index" in 
the codebase, so it's even more unclear what "ind" is supposed to mean.

Updated patch follows.  Please let me know if you have any objections,


- Paul

From: Atish Patra <atishp@rivosinc.com>

RISC-V: Define indirect CSR access helpers

The indirect CSR requires multiple instructions to read/write CSR.
Add a few helper functions for ease of usage.

Signed-off-by: Atish Patra <atishp@rivosinc.com>
Reviewed-by: Charlie Jenkins <thecharlesjenkins@gmail.com>
Tested-by: Charlie Jenkins <thecharlesjenkins@gmail.com>
Link: https://patch.msgid.link/20260701-counter_delegation-v8-5-7909f863a645@meta.com
[pjw@kernel.org: expand "ind" abbreviation; use static inline functions rather than macros]
Signed-off-by: Paul Walmsley <pjw@kernel.org>
---
 arch/riscv/include/asm/csr_indirect.h | 51 +++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 arch/riscv/include/asm/csr_indirect.h

diff --git a/arch/riscv/include/asm/csr_indirect.h b/arch/riscv/include/asm/csr_indirect.h
new file mode 100644
index 000000000000..3cd6a9059455
--- /dev/null
+++ b/arch/riscv/include/asm/csr_indirect.h
@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef _ASM_RISCV_CSR_INDIRECT_H
+#define _ASM_RISCV_CSR_INDIRECT_H
+
+#include <linux/types.h>
+#include <linux/irqflags.h>
+
+#include <asm/csr.h>
+
+static inline unsigned long csr_indirect_read(u16 iregcsr, u32 iselbase, u32 iseloff)
+{
+	unsigned long __value = 0;
+	unsigned long __flags;
+
+	local_irq_save(__flags);
+	csr_write(CSR_ISELECT, iselbase + iseloff);
+	__value = csr_read(iregcsr);
+	local_irq_restore(__flags);
+
+	return __value;
+}
+
+static inline void csr_indirect_write(u16 iregcsr, u32 iselbase, u32 iseloff, unsigned long value)
+{
+	unsigned long __flags;
+
+	local_irq_save(__flags);
+	csr_write(CSR_ISELECT, iselbase + iseloff);
+	csr_write(iregcsr, (value));
+	local_irq_restore(__flags);
+}
+
+static inline unsigned long csr_indirect_warl(u16 iregcsr, u32 iselbase, u32 iseloff,
+					      unsigned long warl_val)
+{
+	unsigned long __old_val = 0, __value = 0;
+	unsigned long __flags;
+
+	local_irq_save(__flags);
+	csr_write(CSR_ISELECT, iselbase + iseloff);
+	__old_val = csr_read(iregcsr);
+	csr_write(iregcsr, warl_val);
+	__value = csr_read(iregcsr);
+	csr_write(iregcsr, __old_val);
+	local_irq_restore(__flags);
+
+	return __value;
+}
+
+#endif
-- 
2.53.0



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