Hi Andrew, On Fri, Jun 28, 2019 at 09:35:24AM +0100, Andrew Murray wrote: [...] > > > @@ -454,7 +458,8 @@ static void etm4_disable_hw(void *info) > > > control &= ~0x1; > > > > > > /* make sure everything completes before disabling */ > > > - mb(); > > > + /* As recommended by 7.3.77 of ARM IHI 0064D */ > > > + dsb(sy); > > > > Here the old code should be right, mb() is the same thing with > > dsb(sy). > > > > So we don't need to change at here? > > Correct - on arm64 there is no difference between mb and dsb(sy) so no > functional change on this hunk. > > In repsonse to Suzuki's feedback on this patch, I've updated the commit > message to describe why I've made this change, as follows: > > "On armv8 the mb macro is defined as dsb(sy) - Given that the etm4x is > only used on armv8 let's directly use dsb(sy) instead of mb(). This > removes some ambiguity and makes it easier to correlate the code with > the TRM." > > Does that make sense? On reason for preferring to use mb() rather than dsb(sy) is for compatibility cross different architectures (armv7, armv8, and so on ...). Seems to me mb() is a general API and transparent for architecture's difference. dsb(sy) is quite dependent on specific Arm architecture, e.g. some old Arm architecures might don't support dsb(sy); and we are not sure later it will change for new architectures. Thanks, Leo Yan
