On Fri, Jun 28, 2019 at 04:51:54PM +0800, Leo Yan wrote: > 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. Yes but please note that the KConfig for this driver depends on ARM64. Thanks, Andrew Murray > > Thanks, > Leo Yan
