On 27 March 2017 at 18:50, Peter Zijlstra <[email protected]> wrote: > On Fri, Mar 24, 2017 at 02:08:58PM +0000, Juri Lelli wrote: >> Worker kthread needs to be able to change frequency for all other >> threads. >> >> Make it special, just under STOP class. > > *yuck* ;-) > > So imagine our I2C/SPI bus is 'busy' and its mutex taken, then this > 'soecial' task will need to boost it. Now add BWI to your thinking and > shudder. > > > On IRC broonie mentioned that: > > - most PMIC operations are fire and forget (no need to wait for a > response). > - PMIC 'packets' are 'small'. > - SPI has the possibility to push stuff on the queue. > > Taken together this seems to suggest we can rework cpufreq drivers to > function in-context, either directly push the packet on the bus if > available, or queue it and let whoever owns it sort it without blocking. > > It might be possible to rework/augment I2C to also support pushing stuff > on a queue.
But sending new voltage value to PMIC is only part of the sequence. When cpufreq set a new opp, it does -set new voltage -wait for the voltage to settle down. -set the new clock frequency you can even have to switch to an intermediate clock source. When such sequence is managed by the kernel, we can't easily git ride of a kthread > > > So if we can make all that work, we can do away with this horrible > horrible kthread. Which is, IMO, a much better solution. > > Thoughts?
