[U-Boot] [RFC PATCH v1 0/1] MIPS64 timer bug

[Chris Packham]

Hi,

We found this on a custom MIPS64 based board. Basically we were seeing
udelay and friends do odd things occasionally. The problem appears to be
when we read the c0 32-bit counter sometimes we get unexpected values
when this is returned as an unsigned long on a 64-bit system. I've
written a little test program (below) that demonstrates the what I think
is problem, it'll work on a x86_64 desktop. I don't know the ins and
outs of the C specifications to comment on if this is a compiler bug but
I still think we should be treating the c0 registers as unsigned
regardless.

 $ cat test.c
 #include <stdio.h>

 int main(int argc, char *argv[])
 {
         int a;
         unsigned long b;

         a = 0x80000000;
         b = a;

         printf("sizeof(int) = %zu\n", sizeof(int));
         printf("sizeof(unsigned long) = %zu\n", sizeof(unsigned long));
         printf("a = %d\n", a);
         printf("a = %x\n", a);
         printf("b = %lu\n", b);
         printf("b = %lx\n", b);

         return 0;
 }

Which yields the following output

 $ ./test
 sizeof(int) = 4
 sizeof(unsigned long) = 8
 a = -2147483648
 a = 80000000
 b = 18446744071562067968
 b = ffffffff80000000

And for completeness
  $ gcc --version
  gcc (Ubuntu 4.8.4-2ubuntu1~14.04) 4.8.4
  Copyright (C) 2013 Free Software Foundation, Inc.

Our embedded target is using
 $ mips64-octeon-linux-gnu-gcc --version
 mips64-octeon-linux-gnu-gcc (GCC) 4.7.0
 Copyright (C) 2012 Free Software Foundation, Inc.



Chris Packham (1):
  mips: Use unsigned int when reading c0 registers

 arch/mips/include/asm/mipsregs.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

-- 
2.5.0.rc0