Re: [PATCH] riscv: acpi: Handle LPI architectural context loss flags

From: Yixun Lan <dlan@kernel.org>
To: Peixin Xie <peixin.xie@linux.spacemit.com>
Cc: Paul Walmsley <pjw@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Alexandre Ghiti <alex@ghiti.fr>,
	Sudeep Holla <sudeep.holla@kernel.org>,
	Oza Pawandeep <quic_poza@quicinc.com>,
	Will Deacon <will@kernel.org>,
	"Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
	linux-acpi@vger.kernel.org, linux-riscv@lists.infradead.org,
	linux-kernel@vger.kernel.org, spacemit@lists.linux.dev,
	stable@vger.kernel.org
Subject: Re: [PATCH] riscv: acpi: Handle LPI architectural context loss flags
Date: Tue, 28 Jul 2026 11:17:51 +0000	[thread overview]
Message-ID: <20260728111751-GKC76518@kernel.org> (raw)
In-Reply-To: <20260728-riscv-acpi-lpi-timer-v1-1-c722bce01e48@linux.spacemit.com>

Hi Peixin,

On 17:36 Tue 28 Jul     , Peixin Xie wrote:
> Commit 4785aa802853 ("cpuidle, ACPI: Evaluate LPI arch_flags for
> broadcast timer") replaced the generic nonzero check for LPI
> architectural context loss flags with arch_get_idle_state_flags().
> RISC-V does not implement the helper, so it falls back to the stub
> that returns 0. Consequently, CPUIDLE_FLAG_TIMER_STOP is not set when
> an LPI state loses the hart timer context, preventing cpuidle from
> using a broadcast timer for that state.
> 
> Implement the RISC-V helper and map the hart timer context loss flag
> to CPUIDLE_FLAG_TIMER_STOP.
> 
> Fixes: 4785aa802853 ("cpuidle, ACPI: Evaluate LPI arch_flags for broadcast timer")
> Cc: stable@vger.kernel.org
> Signed-off-by: Peixin Xie <peixin.xie@linux.spacemit.com>
Looks good to me, with one minor comment

Reviewed-by: Yixun Lan <dlan@kernel.org>

> ---
>  arch/riscv/include/asm/acpi.h | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/arch/riscv/include/asm/acpi.h b/arch/riscv/include/asm/acpi.h
> index 26ab37c171bc..3a3da834c340 100644
> --- a/arch/riscv/include/asm/acpi.h
> +++ b/arch/riscv/include/asm/acpi.h
> @@ -12,6 +12,8 @@
>  #ifndef _ASM_ACPI_H
>  #define _ASM_ACPI_H
>  
> +#include <linux/cpuidle.h>
> +
>  /* Basic configuration for ACPI */
>  #ifdef CONFIG_ACPI
>  
> @@ -67,6 +69,23 @@ int acpi_get_riscv_isa(struct acpi_table_header *table,
>  
>  void acpi_get_cbo_block_size(struct acpi_table_header *table, u32 *cbom_size,
>  			     u32 *cboz_size, u32 *cbop_size);
> +
> +/*
> + * RISC-V Functional Fixed Hardware Specification Version v1.0.1
> + * Table 4: LPI Arch. Context Lost Flags

As I checked https://docs.riscv.org/reference/acpi-ffh/v1.0.1/ffh_use_cases.html
It's table 3, and I'd suggest to put more precisely as:

"Chapter 2.1.1.2. Arch. Context Lost Flags, Table 3"

> + */
> +#define RISCV_LPI_HART_TIMER_CTXT_LOST		BIT(0)
> +
> +static inline unsigned int arch_get_idle_state_flags(u32 arch_flags)
> +{
> +	if (arch_flags & RISCV_LPI_HART_TIMER_CTXT_LOST)
> +		return CPUIDLE_FLAG_TIMER_STOP;
> +
> +	return 0;
> +}
> +
> +#define arch_get_idle_state_flags arch_get_idle_state_flags
> +
>  #else
>  static inline void acpi_init_rintc_map(void) { }
>  static inline struct acpi_madt_rintc *acpi_cpu_get_madt_rintc(int cpu)
> 
> ---
> base-commit: 1d6f0a217c662693d2307ee06851cb4bfcbf9529
> change-id: 20260727-riscv-acpi-lpi-timer-6f1739a6c831
> 
> Best regards,
> --  
> Peixin Xie <peixin.xie@linux.spacemit.com>
> 

-- 
Yixun Lan (dlan)

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