On Thu, Mar 05, 2015 at 02:29:50PM +0530, Viresh Kumar wrote:
On 5 March 2015 at 13:12, Sascha Hauer s.hauer@pengutronix.de wrote:
We have clk_set_parent for changing the parent and clk_set_rate to change the rate. Use the former for changing the parent and the latter for changing the rate. What you are interested in is changing the parent, so use clk_set_parent for this and not abuse a side effect of clk_set_rate.
clk_set_rate() for CPUs clock is responsible to change clock rate of the CPU. Whether it plays with PLLs or muxes, its not that relevant.
My suggestion is to take another approach. Implement clk_set_rate for these muxes and in the set_rate hook:
- switch mux to intermediate PLL parent
- call clk_set_rate() for the real parent PLL
- switch mux back to real parent PLL
This way the things happening behind the scenes are completely transparent to the cpufreq driver and you can use cpufreq-dt as is without changes.
CPUFreq wants to change to intermediate frequency by itself against some magic change behind the scene. The major requirement for that comes from the fact that we want to send PRE/POST freq notifiers on which loops-per-jiffie depends.
You could register a clk notifier using clk_notifier_register(). The notifer callback can then call the cpufreq notifiers. The clk notifiers can also be used to change the CPU voltage.
Sascha