linux-kernel - Re: [PATCH] ACPI: CPPC: fix bug that causes the value written in cpc register to be wrong.

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Message-ID: <dfe6ca13-7c4b-4204-b3fb-7390eca3b18b@rivosinc.com>
Date: Wed, 13 Nov 2024 08:05:02 +0100
From: Clément Léger <cleger@...osinc.com>
To: Lifeng Zheng <zhenglifeng1@...wei.com>, rafael@...nel.org, lenb@...nel.org
Cc: linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
 zhanjie9@...ilicon.com, lihuisong@...wei.com, fanghao11@...wei.com
Subject: Re: [PATCH] ACPI: CPPC: fix bug that causes the value written in cpc
 register to be wrong.

On 13/11/2024 03:49, Lifeng Zheng wrote:
> With these codes, the value written in cpc register will be the result of
> the OR operatiion on input value and prev_val. This will causes the value
> to be wrong.
> 
> Signed-off-by: Lifeng Zheng <zhenglifeng1@...wei.com>
> ---
>  drivers/acpi/cppc_acpi.c | 1 -
>  1 file changed, 1 deletion(-)
> 
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 01192fd047a6..f69ef7cc0caf 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -1146,7 +1146,6 @@ static int cpc_write(int cpu, struct cpc_register_resource *reg_res, u64 val)
>  			return -EFAULT;
>  		}
>  		val = MASK_VAL_WRITE(reg, prev_val, val);
> -		val |= prev_val;

Hi Lifeng,

Indeed, MASK_VAL_WRITE() already takes care of ORing prev_val with the
register mask. You can also add a Fixes:

Fixes: 60949b7b8054 ("ACPI: CPPC: Fix MASK_VAL() usage")

Thanks,

Clément

>  	}
>  
>  	switch (size) {