On 01/18/2018 11:11 AM, Alexey Brodkin wrote: > Hi Vineet, > > On Thu, 2018-01-18 at 10:54 -0800, Vineet Gupta wrote: >> On 01/18/2018 05:48 AM, Alexey Brodkin wrote: >>> HS48 core starts with dual-issue enabled but in some cases like >>> debugging as well as benchmarking it might be useful to disable >>> dual-issue for a particular run. >>> >>> Note: >>> 1. To disable dual-issue user has to change a value of a global variable >>> in target's memory right before start of Linu kernel execution >>> (most probably via JTAG) >>> >>> 2. Disabling happens very early on boot and to get it back enabled it's >>> required to restart Linux kernel. I.e. with this change we don't allow >>> toggling dual-issue state in random moments of run-time >> But we need access to a debugger anyways to change this global variable. >> If you already have that won't it be better to change the aux register itself from >> the debugger itself. >> I don't really see how the global variable way of toggle adds any value here ? > I think there's some sense in a global variable. > > 1. Not sure if OpenOCD/GDB pair for ARC allows to read/write random AUX regs. > Probably allows but I guess we'll need a new .xml description which lists EXEC_CTRL > AUX reg. Correct me if I'm wrong here. Not sure of this a strong argument ... > > 2. If somebody wants to disable dual-issue persistently (here I mean building an image > which had dual-issue disabled and there's no need to alter anything after image loading) Ok this is more reasonable ! But can we do this in early boot code then. There's a fair bit of code leading up to where we are doing now so I'd prefer we do it just as we do for disabling L1 caches. Please note that SLC / IOC are special - as much as I liked to do them super early - we can't as there's fair bit of code bloat / mem size etc which we don't knwo that early. > then it's possible just to change a simple and very obvious line in arch/arc/kernel/setup.c > other than trying to guess what could be good place in sources to stick that AUX reg write. > Note we don't explicitly do reads of AUX_EXEC_CTRL instead we just use READ_BCR macro so > for newcomers it might not be immediately obvious what to do and where. > Add the fact that logic of the flag is reversed... > > -Alexey
