linux-kernel - Re: [PATCH] cpufreq/amd-pstate: Fix amd_pstate mode switch on shared memory systems

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Message-ID: <ab486635-1827-49b5-9e5f-73f62b86c82a@amd.com>
Date: Mon, 7 Oct 2024 11:31:45 -0500
From: Mario Limonciello <mario.limonciello@....com>
To: Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>
Cc: linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
 gautham.shenoy@....com, perry.yuan@....com, ray.huang@....com,
 rafael@...nel.org, viresh.kumar@...aro.org
Subject: Re: [PATCH] cpufreq/amd-pstate: Fix amd_pstate mode switch on shared
 memory systems

On 10/4/2024 07:23, Dhananjay Ugwekar wrote:
> While switching the driver mode between active and passive, Collaborative
> Processor Performance Control (CPPC) is disabled in
> amd_pstate_unregister_driver(). But, it is not enabled back while registering
> the new driver (passive or active). This leads to the new driver mode not
> working correctly, so enable it back in amd_pstate_register_driver().
> 
> Fixes: 3ca7bc818d8c ("cpufreq: amd-pstate: Add guided mode control support via sysfs")
> Signed-off-by: Dhananjay Ugwekar <Dhananjay.Ugwekar@....com>

Reviewed-by: Mario Limonciello <mario.limonciello@....com>

I think as a minimally risky fix to go to 6.12-rcX this makes sense, but 
looking at all this code there is a bit of duplication that exists that 
we should do a more general cleanup for 6.13.

So I'll queue this up in my -fixes branch for 6.12-rcX. but please do 
the bigger cleanup as a follow up that we can land for 6.13.

> ---
>   drivers/cpufreq/amd-pstate.c | 10 ++++++++++
>   1 file changed, 10 insertions(+)
> 
> diff --git a/drivers/cpufreq/amd-pstate.c b/drivers/cpufreq/amd-pstate.c
> index cdc08d2ddd52..4acf5fbeb116 100644
> --- a/drivers/cpufreq/amd-pstate.c
> +++ b/drivers/cpufreq/amd-pstate.c
> @@ -1191,11 +1191,21 @@ static int amd_pstate_register_driver(int mode)
>   		return -EINVAL;
>   
>   	cppc_state = mode;
> +
> +	ret = amd_pstate_enable(true);
> +	if (ret) {
> +		pr_err("failed to enable cppc during amd-pstate driver registration, return %d\n",
> +		       ret);
> +		amd_pstate_driver_cleanup();
> +		return ret;
> +	}
> +
>   	ret = cpufreq_register_driver(current_pstate_driver);
>   	if (ret) {
>   		amd_pstate_driver_cleanup();
>   		return ret;
>   	}
> +
>   	return 0;
>   }
>