devfreq: Add CPUBW HW monitor governor
The CPUBW HW monitor devfreq governor uses the Krait L2 PM counters to
determine the bandwidth needed by the Krait CPU subsystem. This governor
can be used in conjunction with the CPUBW devfreq device to dynamically
scale the DDR frequency based on the demand/actual usage from the Krait CPU
subsystem. Since this governor uses the Krait L2 PM counters it can
conflict with certain profiling tools.
The Krait L2 performance monitor counters have the capability to count the
no. of read/write transactions going out the master ports. They also have
the capability to raise interrupts when they overflow. This driver uses
those counters to determine the true usage of DDR from the Krait processor
subsystem and then recommends CPU DDR BW votes based on the measured values
and the following tunable parameters.
The driver provides various tunables that allow it to be tuned more in
favor of power or performance:
- io_percent: The percentage of the CPU time that can be spent waiting on
memory I/O. Lower value is better performance and worse power.
- sample_ms: The sampling period in milliseconds. This only affects the
sampling period when DDR use is ramping down or is increasing very slowly
(See tolerance_percent).
- tolerance_percent: The minimum increase in DDR use, compared to previous
sample, that will trigger an IRQ to immediately bump up the bandwidth
vote. It's expressed as a percentage of the previous sampled DDR use.
- decay_rate: The parameter controls the rate at which the history is
forgotten when ramping down. This is expressed as a percentage of history
to be forgotten. So 100% means ignore history, 0% mean never forget the
historical max. The default 90% means forget 90% of history each time.
- guard_band_mbps: This is a margin that's added to the measured BW (and
hence also the Bus BW votes) that's present to account for the time it
takes to ramp up the DDR BW while the CPU continues to use the DDR.
- bw_step: All BW votes are rounded up to multiples of bw_step. The default
value is 200 MB/s that turns out to ~25 or 12.5 MHz based on the SoC. A
smaller value would mean more frequent bus BW changes. A higher value
would mean less frequent BW vote updates, but also means at times an
unnecessarily higher BW vote (due to the rounding up).
Change-Id: I88629a3e545cdca7160af8f8ca616ecc949d9947
Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
diff --git a/drivers/devfreq/governor_bw_hwmon.h b/drivers/devfreq/governor_bw_hwmon.h
new file mode 100644
index 0000000..c5779b5
--- /dev/null
+++ b/drivers/devfreq/governor_bw_hwmon.h
@@ -0,0 +1,74 @@
+/*
+ * Copyright (c) 2014-2016, The Linux Foundation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ */
+
+#ifndef _GOVERNOR_BW_HWMON_H
+#define _GOVERNOR_BW_HWMON_H
+
+#include <linux/kernel.h>
+#include <linux/devfreq.h>
+
+/**
+ * struct bw_hwmon - dev BW HW monitor info
+ * @start_hwmon: Start the HW monitoring of the dev BW
+ * @stop_hwmon: Stop the HW monitoring of dev BW
+ * @is_valid_irq: Check whether the IRQ was triggered by the
+ * counters used to monitor dev BW.
+ * @meas_bw_and_set_irq: Return the measured bandwidth and set up the
+ * IRQ to fire if the usage exceeds current
+ * measurement by @tol percent.
+ * @irq: IRQ number that corresponds to this HW
+ * monitor.
+ * @dev: Pointer to device that this HW monitor can
+ * monitor.
+ * @of_node: OF node of device that this HW monitor can
+ * monitor.
+ * @gov: devfreq_governor struct that should be used
+ * when registering this HW monitor with devfreq.
+ * Only the name field is expected to be
+ * initialized.
+ * @df: Devfreq node that this HW monitor is being
+ * used for. NULL when not actively in use and
+ * non-NULL when in use.
+ *
+ * One of dev, of_node or governor_name needs to be specified for a
+ * successful registration.
+ *
+ */
+struct bw_hwmon {
+ int (*start_hwmon)(struct bw_hwmon *hw, unsigned long mbps);
+ void (*stop_hwmon)(struct bw_hwmon *hw);
+ unsigned long (*meas_bw_and_set_irq)(struct bw_hwmon *hw,
+ unsigned int tol, unsigned int us);
+ struct device *dev;
+ struct device_node *of_node;
+ struct devfreq_governor *gov;
+
+ struct devfreq *df;
+};
+
+#ifdef CONFIG_DEVFREQ_GOV_QCOM_BW_HWMON
+int register_bw_hwmon(struct device *dev, struct bw_hwmon *hwmon);
+int update_bw_hwmon(struct bw_hwmon *hwmon);
+#else
+static inline int register_bw_hwmon(struct device *dev,
+ struct bw_hwmon *hwmon)
+{
+ return 0;
+}
+int update_bw_hwmon(struct bw_hwmon *hwmon)
+{
+ return 0;
+}
+#endif
+
+#endif /* _GOVERNOR_BW_HWMON_H */