linux-kernel - Re: [PATCH 5/6] cppc_acpi: print error message if CPPC is unsupported

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Message-ID: <9f6bea2e-7291-4cf8-a407-8c13653ca10e@amd.com>
Date: Wed, 31 Jan 2024 15:51:33 -0600
From: Mario Limonciello <mario.limonciello@....com>
To: Perry Yuan <perry.yuan@....com>, rafael.j.wysocki@...el.com,
 viresh.kumar@...aro.org, Ray.Huang@....com, gautham.shenoy@....com,
 Borislav.Petkov@....com
Cc: Alexander.Deucher@....com, Xinmei.Huang@....com, Xiaojian.Du@....com,
 Li.Meng@....com, linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] cppc_acpi: print error message if CPPC is unsupported

On 1/31/2024 02:50, Perry Yuan wrote:
> to be more clear what is wrong with CPPC when pstate driver failed to
> load which has dependency on the CPPC capabilities.
> 
> Add one more debug message to notify user if CPPC is not supported by
> the CPU, then it will be easy to find out what need to fix for pstate
> driver loading issue.
> 
> [    0.477523] amd_pstate: the _CPC object is not present in SBIOS or ACPI disabled
> 
> Above message is not clear enough to verify whether CPPC is not supported.
> 
> Signed-off-by: Perry Yuan <perry.yuan@....com>
> ---
>   drivers/acpi/cppc_acpi.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 7ff269a78c20..217c11c12b57 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -676,8 +676,10 @@ int acpi_cppc_processor_probe(struct acpi_processor *pr)
>   
>   	if (!osc_sb_cppc2_support_acked) {
>   		pr_debug("CPPC v2 _OSC not acked\n");
> -		if (!cpc_supported_by_cpu())
> -			return -ENODEV;
> +		if (!cpc_supported_by_cpu()) {
> +				pr_debug("CPPC is not supported\n");

I would argue this doesn't add any value to a user.  To help a user it 
should be "CPPC is not supported by the CPU".

> +				return -ENODEV;
> +			}

This whitespace is wrong

>   	}
>   
>   	/* Parse the ACPI _CPC table for this CPU. */