Re: [PATCH] cpuidle: riscv-sbi: Stop using non-retentive suspend

From: Conor Dooley <conor@kernel.org>
To: Palmer Dabbelt <palmer@rivosinc.com>
Cc: anup@brainfault.org, rafael@kernel.org,
	daniel.lezcano@linaro.org,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	aou@eecs.berkeley.edu, linux-pm@vger.kernel.org,
	linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux@rivosinc.com
Subject: Re: [PATCH] cpuidle: riscv-sbi: Stop using non-retentive suspend
Date: Mon, 21 Nov 2022 21:10:39 +0000	[thread overview]
Message-ID: <Y3vpT2XoylY4i2kx@spud> (raw)
In-Reply-To: <20221121205647.23343-1-palmer@rivosinc.com>

On Mon, Nov 21, 2022 at 12:56:47PM -0800, Palmer Dabbelt wrote:
> From: Palmer Dabbelt <palmer@rivosinc.com>
> 
> As per [1], whether or not the core can wake up from non-retentive
> suspend is a platform-specific detail.  We don't have any way to encode
> that, so just stop using them until we've sorted that out.

For anyone playing along at home, Anup had a proposal for encoding this
information (yoinked from the GH issue below):
https://lore.kernel.org/all/20220727114302.302201-1-apatel@ventanamicro.com/> 

> Link: https://github.com/riscv-non-isa/riscv-sbi-doc/issues/98#issuecomment-1288564687
> Fixes: 6abf32f1d9c5 ("cpuidle: Add RISC-V SBI CPU idle driver")
> Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
> 
> ---
> 
> This should allow us to revert 232ccac1bd9b ("clocksource/drivers/riscv:
> Events are stopped during CPU suspend"), which fixes suspend on the D1
> but breaks timers everywhere.

FWIW the revert is at:
https://lore.kernel.org/linux-riscv/20221023185444.678573-1-conor@kernel.org/

Commit message is probably a little lacking as I didn't understand the
problem when I wrote it. I'll respin the revert with a tidier message
tomorrow.

Acked-by: Conor Dooley <conor.dooley@microchip.com>

> ---
>  drivers/cpuidle/cpuidle-riscv-sbi.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/cpuidle/cpuidle-riscv-sbi.c b/drivers/cpuidle/cpuidle-riscv-sbi.c
> index 05fe2902df9a..9d1063a54495 100644
> --- a/drivers/cpuidle/cpuidle-riscv-sbi.c
> +++ b/drivers/cpuidle/cpuidle-riscv-sbi.c
> @@ -214,6 +214,17 @@ static bool sbi_suspend_state_is_valid(u32 state)
>  	if (state > SBI_HSM_SUSPEND_NON_RET_DEFAULT &&
>  	    state < SBI_HSM_SUSPEND_NON_RET_PLATFORM)
>  		return false;
> +
> +	/*
> +	 * Whether or not RISC-V systems deliver interrupts to harts in a
> +	 * non-retentive suspend state is a platform-specific detail.  This can
> +	 * leave the hart unable to wake up, so just mark these states as
> +	 * unsupported until we have a mechanism to expose these
> +	 * platform-specific details to Linux.
> +	 */
> +	if (state & SBI_HSM_SUSP_NON_RET_BIT)
> +		return false;
> +
>  	return true;
>  }
>  
> -- 
> 2.38.1
> 