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Message-ID: <47ded4da-5c39-9132-7978-d0f8c8ee0318@arm.com>
Date:   Wed, 19 Jul 2023 09:39:53 +0100
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Subject: Re: [PATCH] Revert "thermal: power allocator: change the 'k_*' always
 in estimate_pid_constants()"
Content-Language: en-US
To:     Di Shen <di.shen@unisoc.com>
Cc:     linux-pm@vger.kernel.org, rui.zhang@intel.com, rafael@kernel.org,
        daniel.lezcano@linaro.org, linux-kernel@vger.kernel.org,
        xuewen.yan@unisoc.com, jeson.gao@unisoc.com, orsonzhai@gmail.com,
        zhanglyra@gmail.com, amitk@kernel.org
References: <20230712084840.3594-1-di.shen@unisoc.com>
From:   Lukasz Luba <lukasz.luba@arm.com>
In-Reply-To: <20230712084840.3594-1-di.shen@unisoc.com>
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Precedence: bulk

Hi Di,

On 7/12/23 09:48, Di Shen wrote:
> This reverts commit 90a996544946d1d4834ec2ec8add586edd905779.
> 
> The commit ensures that the pid constants are updated when
> sustainable_power changes, but it makes it impossible for
> the driver to set the pid constants when the sustainable_power
> is not changed.
> 
> When the driver tries to register a thermal zone device by
> thermal_zone_device_register_with_trips(const char *type,
> 	struct thermal_trip *trips, int num_trips, int mask,
> 	void *devdata, struct thermal_zone_device_ops *ops,
> 	struct thermal_zone_params *tzp, int passive_delay,
> 	int polling_delay)
> and passes the private thermal_zone_params structure data,
> 
> thermal_zone_devcice_register_with_trips
> 	|
> thermal_set_governor
> 	|
> bind_to_tz
> 	|
> power_allocator_bind
> 	|
> estimate_pid_constants
> 
> the tzp->k_* will not be the data that driver have given,
> but the data estimated by sustainable_power.
> 
> To make it possible for driver to add its own pid constants,

That was dropped, the drivers shouldn't configure 'k_*' IPA
parameters. There was also an ask to add those parameter
values to the DT for setup - also not allowed.

> the 'force' flag is needed to indicate whether the tzp->k_*
> should be estimated by sustainable_power or not.

We don't want to maintain many different ways of configurations,
which can cause bugs in not tested corner cases.

Please use the user-space to change those 'k_*' parameters.
There are this dedicated and safe sysfs interfaces for each
thermal zone.

The phones that I have on my desk do the update of 'k_*' parameters via
sysfs. They do this in different scenarios. You can try to derive
best 'k_*' values for your workload scenarios and than save
them in the config file. You can update in runtime from user-space
when you switch to your scenario (e.g. camera, game, video call).

Regards,
Lukasz