linux-kernel - [PATCH 16/17] Documentation: EM: Add example with driver modifying the EM

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Message-Id: <20230314103357.26010-17-lukasz.luba@arm.com>
Date:   Tue, 14 Mar 2023 10:33:56 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        rafael@...nel.org
Cc:     lukasz.luba@....com, dietmar.eggemann@....com, rui.zhang@...el.com,
        amit.kucheria@...durent.com, amit.kachhap@...il.com,
        daniel.lezcano@...aro.org, viresh.kumar@...aro.org,
        len.brown@...el.com, pavel@....cz, Pierre.Gondois@....com,
        ionela.voinescu@....com, rostedt@...dmis.org, mhiramat@...nel.org
Subject: [PATCH 16/17] Documentation: EM: Add example with driver modifying the EM

The Energy Model (EM) support runtime modifications. Add description
with example driver code which updates EM.

Signed-off-by: Lukasz Luba <lukasz.luba@....com>
---
 Documentation/power/energy-model.rst | 53 ++++++++++++++++++++++++++--
 1 file changed, 51 insertions(+), 2 deletions(-)

diff --git a/Documentation/power/energy-model.rst b/Documentation/power/energy-model.rst
index 64c2462dc9a6..a6ceeeb72868 100644
--- a/Documentation/power/energy-model.rst
+++ b/Documentation/power/energy-model.rst
@@ -225,8 +225,11 @@ or in Section 3.4
    :export:
 
 
-4. Example driver
------------------
+4. Examples
+-----------
+
+4.1 Example driver with EM registration
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 The CPUFreq framework supports dedicated callback for registering
 the EM for a given CPU(s) 'policy' object: cpufreq_driver::register_em().
@@ -280,3 +283,49 @@ EM framework::
   39	static struct cpufreq_driver foo_cpufreq_driver = {
   40		.register_em = foo_cpufreq_register_em,
   41	};
+
+
+4.2 Example driver with EM modification
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+This section provides a simple example of a thermal driver modifying the EM.
+The driver implements a foo_mod_power() function to be provided to the
+EM framework. The driver is woken up periodically to check the temperature
+and modify the EM data if needed::
+
+  -> drivers/thermal/foo_thermal.c
+
+  01	static int foo_mod_power(struct device *dev, unsigned long freq,
+  02			unsigned long *power, void *priv)
+  03	{
+  04		struct foo_context *ctx = priv;
+  05
+  06		/* Estimate power for the given frequency and temperature */
+  07		*power = foo_estimate_power(dev, freq, ctx->temperature);
+  08		if (*power >= EM_MAX_POWER);
+  09			return -EINVAL;
+  10
+  11		return 0;
+  12	}
+  13
+  14	/*
+  15	 * Function called periodically to check the temperature and
+  16	 * update the EM if needed
+  17	 */
+  18	static void foo_thermal_em_update(struct foo_context *ctx)
+  19	{
+  20		struct em_data_callback em_cb = EM_UPDATE_CB(mod_power);
+  21		struct cpufreq_policy *policy = ctx->policy;
+  22		struct device *cpu_dev;
+  23
+  24		cpu_dev = get_cpu_device(cpumask_first(policy->cpus));
+  25
+  26		ctx->temperature = foo_get_temp(cpu_dev, ctx);
+  27		if (ctx->temperature < FOO_EM_UPDATE_TEMP_THRESHOLD)
+  28			return;
+  29
+  30		/* Update EM for the CPUs' performance domain */
+  31		ret = em_dev_update_perf_domain(cpu_dev, &em_cb, ctx);
+  32		if (ret)
+  33			pr_warn("foo_thermal: EM update failed\n");
+  34	}
-- 
2.17.1