On 12/07/2016 07:36 AM, Alexey Brodkin wrote: > We used to think that ARC cores in SMP SoC start > consequentially, i.e. core0 -> core1 -> core2 -> core4. > > Moreover we treat core0 as a master core which does some > low-level initialization before allowing other cores to > start doing real stuff. > > In that case everything works as expected - smp_processor_id() > returns expected values for all cores, i.e.: > 0 for core0 > 1 for core1 etc. > > But what if instead of core0 we want core1 to be the master? > That might be the case if we want to use only one core out of > SMP setup and that core is not core0 or for some other reason > modify core start-up sequence to say: core3 -> core1 > ... > > In that case smp_processor_id() returns values that differ > from real hardware core index. For the first/master core that > we'l get 0, the next one will be 1 etc. But then the problem is you are not setting up thread_info->cpu correctly. And that needs fixing. Say we already had ur next patch which doesn't assume 0 based masters, then is this patch still needed. Essentially this change can be taken as an optimization (mem vz. aux reg read) but I don't think it is a fix ! > The problem here is we'll use improper cpu indexes in MCIP commands > and inevitably commands will be sent to unexpected cores causing all > sorts of unexpected behavior. > > But if we use hardware core index out out IDENTITY AUX reg that problem > won't happen because cpu value will match its hardware index. > > Signed-off-by: Alexey Brodkin <abrodkin at synopsys.com> > Cc: stable at vger.kernel.org > --- > arch/arc/include/asm/smp.h | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/arch/arc/include/asm/smp.h b/arch/arc/include/asm/smp.h > index 0861007d9ef3..5aad65d3defd 100644 > --- a/arch/arc/include/asm/smp.h > +++ b/arch/arc/include/asm/smp.h > @@ -14,8 +14,9 @@ > #include <linux/types.h> > #include <linux/init.h> > #include <linux/threads.h> > +#include <asm/arcregs.h> > > -#define raw_smp_processor_id() (current_thread_info()->cpu) > +#define raw_smp_processor_id() ((int)(read_aux_reg(AUX_IDENTITY) >> 8) & 0xFF) > > /* including cpumask.h leads to cyclic deps hence this Forward declaration */ > struct cpumask;
