Kevin Hilman wrote:
First, this patch adds new worst-case latency values to the omap_device_pm_latency struct. Here the worst-case measured latencies for the activate and deactivate hooks are stored. In addition, add an option to auto-adjust the latency values used for device activate/deactivate. By setting a new 'OMAP_DEVICE_LATENCY_AUTO_ADJUST' flag in the omap_device_pm_latency struct, the omap_device layer automatically adjusts the activate/deactivate latencies to the worst-case measured values. Anytime a new worst-case value is found, it is printed to the console. Here is an example log during boot using UART2 s an example. After boot, the OPP is manually changed to the 125MHz OPP: [...] Freeing init memory: 128K omap_device: serial8250.2: new worst case deactivate latency 0: 30517 omap_device: serial8250.2: new worst case activate latency 0: 30517 omap_device: serial8250.2: new worst case activate latency 0: 218139648 omap_device: serial8250.2: new worst case deactivate latency 0: 61035 omap_device: serial8250.2: new worst case activate latency 0: 278076171 omap_device: serial8250.2: new worst case activate latency 0: 298614501 omap_device: serial8250.2: new worst case activate latency 0: 327331542 / # echo 125000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_setspeed omap_device: serial8250.2: new worst case deactivate latency 0: 91552 Motivation: this can be used as a technique to automatically determine the worst case latency values. The current method of printing a warning on every violation is too noisy to actually interact the console in order to set low OPP to discover latencies.
Another motivation for this patch is that the activate/deactivate latenices can vary depending on the idlemode of the device. While working on the UART I noticed that when using no-idle, the activate latencies were as high as several hundred msecs as shown above. When the UARTs are in smart-idle, the max latency is well under 100 usecs.
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