James Yang <james.y...@freescale.com> wrote on 02/08/2014 07:49:40 AM:
> From: James Yang <james.y...@freescale.com> > To: Gabriel Paubert <paub...@iram.es> > Cc: Stephen N Chivers <schiv...@csc.com.au>, Chris Proctor > <cproc...@csc.com.au>, <linuxppc-dev@lists.ozlabs.org> > Date: 02/08/2014 07:49 AM > Subject: Re: arch/powerpc/math-emu/mtfsf.c - incorrect mask? > > On Fri, 7 Feb 2014, Gabriel Paubert wrote: > > > Hi Stephen, > > > > On Fri, Feb 07, 2014 at 11:27:57AM +1000, Stephen N Chivers wrote: > > > Gabriel Paubert <paub...@iram.es> wrote on 02/06/2014 07:26:37 PM: > > > > > > > From: Gabriel Paubert <paub...@iram.es> > > > > To: Stephen N Chivers <schiv...@csc.com.au> > > > > Cc: linuxppc-dev@lists.ozlabs.org, Chris Proctor <cproc...@csc.com.au> > > > > Date: 02/06/2014 07:26 PM > > > > Subject: Re: arch/powerpc/math-emu/mtfsf.c - incorrect mask? > > > > > > > > On Thu, Feb 06, 2014 at 12:09:00PM +1000, Stephen N Chivers wrote: > > > > > > > > > > > mask = 0; > > > > > if (FM & (1 << 0)) > > > > > mask |= 0x0000000f; > > > > > if (FM & (1 << 1)) > > > > > mask |= 0x000000f0; > > > > > if (FM & (1 << 2)) > > > > > mask |= 0x00000f00; > > > > > if (FM & (1 << 3)) > > > > > mask |= 0x0000f000; > > > > > if (FM & (1 << 4)) > > > > > mask |= 0x000f0000; > > > > > if (FM & (1 << 5)) > > > > > mask |= 0x00f00000; > > > > > if (FM & (1 << 6)) > > > > > mask |= 0x0f000000; > > > > > if (FM & (1 << 7)) > > > > > mask |= 0x90000000; > > > > > > > > > > With the above mask computation I get consistent results for > > > > > both the MPC8548 and MPC7410 boards. > > > > > > > > > > Am I missing something subtle? > > > > > > > > No I think you are correct. This said, this code may probably be > > > optimized > > > > to eliminate a lot of the conditional branches. I think that: > > > If the compiler is enabled to generate isel instructions, it would not > use a conditional branch for this code. (ignore the andi's values, > this is an old compile) > >From limited research, the 440GP is a processor that doesn't implement the isel instruction and it does not implement floating point. The kernel emulates isel and so using that instruction for the 440GP would have a double trap penalty. Correct me if I am wrong, the isel instruction first appears in PowerPC ISA v2.04 around mid 2007. Stephen Chivers, CSC Australia Pty. Ltd. _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
