Re: [PATCH v6 04/21] RISC-V: Define indirect CSR access helpers

From: Charlie Jenkins <thecharlesjenkins@gmail.com>
To: Atish Patra <atish.patra@linux.dev>
Cc: James Clark <james.clark@linaro.org>,
	Rob Herring <robh@kernel.org>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Jiri Olsa <jolsa@kernel.org>, Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Anup Patel <anup@brainfault.org>,
	Namhyung Kim <namhyung@kernel.org>,
	Paul Walmsley <pjw@kernel.org>,
	Krzysztof Kozlowski <krzk+dt@kernel.org>,
	Ian Rogers <irogers@google.com>,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-perf-users@vger.kernel.org, Conor Dooley <conor@kernel.org>,
	devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v6 04/21] RISC-V: Define indirect CSR access helpers
Date: Sun, 21 Jun 2026 23:42:15 -0700	[thread overview]
Message-ID: <ajjZR-R11yPYWuDp@blinky> (raw)
In-Reply-To: <20260608-counter_delegation-v6-4-285b72ed65a9@meta.com>

On Mon, Jun 08, 2026 at 11:01:18PM -0700, Atish Patra wrote:
> From: Atish Patra <atishp@rivosinc.com>
> 
> The indriect CSR requires multiple instructions to read/write CSR.

indirect

> Add a few helper functions for ease of usage.
> 
> Signed-off-by: Atish Patra <atishp@rivosinc.com>
> ---
>  arch/riscv/include/asm/csr_ind.h | 44 ++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 44 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/csr_ind.h b/arch/riscv/include/asm/csr_ind.h
> new file mode 100644
> index 000000000000..6fd7d44dc640
> --- /dev/null
> +++ b/arch/riscv/include/asm/csr_ind.h
> @@ -0,0 +1,44 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2024 Rivos Inc.

I don't think it makes sense to introduce this copyright in new commits.

- Charlie

> + */
> +
> +#ifndef _ASM_RISCV_CSR_IND_H
> +#define _ASM_RISCV_CSR_IND_H
> +
> +#include <linux/irqflags.h>
> +
> +#include <asm/csr.h>
> +
> +#define csr_ind_read(iregcsr, iselbase, 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);				\
> +	__value;						\
> +})
> +
> +#define csr_ind_write(iregcsr, iselbase, iseloff, value) ({	\
> +	unsigned long __flags;					\
> +	local_irq_save(__flags);				\
> +	csr_write(CSR_ISELECT, (iselbase) + (iseloff));		\
> +	csr_write(iregcsr, (value));				\
> +	local_irq_restore(__flags);				\
> +})
> +
> +#define csr_ind_warl(iregcsr, iselbase, iseloff, 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);				\
> +	__value;						\
> +})
> +
> +#endif
> 
> -- 
> 2.53.0-Meta
> 
> 
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