On Wed, Mar 29, 2017 at 04:17:19PM +0100, Mike Leach wrote: [...] > >> >+out_powered_up: > >> >+ debug_os_unlock(drvdata); > >> > >> Question: Do we need a matching debug_os_lock() once we are done ? > > > > I have checked ARM ARMv8, but there have no detailed description for > > this. I refered coresight-etmv4 code and Mike's pseudo code, ther have > > no debug_os_lock() related operations. > > > > Mike, Mathieu, could you also help confirm this? > > > > Debug OS lock / unlock allows the power management code running on the > core to lock out the external debugger while the debug registers are > saved/restored during a core power event. > > e.g. A sequence such as this might occur in a correctly programmed system.... > > debug_os_lock() > save_debug_regs() // visible from core power domain - incl breakpoints etc > save_etm_regs() > ... // other stuff prior to core power down, > <power_down_core> > > Followed by... > > <power_up_core> > restore_etm_regs() > restore_debug_regs() // visible from core power domain - incl breakpoints etc > debug_os_unlock() > > The value is 1 (locked) if cold resetting into AArch64 - it is > expected that some system software will set this to 0 as part of the > boot process. > The lock prevents write access to the external debug registers so we > need to clear it to set up the external debug registers we are using. This description is conflict with upper restoring flows. During restore_debug_regs(), the os lock is locked so how it can write external debug register to restore context? > This suggests that it should be restored as we found it when done. Thanks, Leo Yan -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
