[U-Boot] [Resend RFC PATCH v2] mips: Use unsigned int when reading c0 registers

Daniel Schwierzeck
2015-07-18T09:29:33Z

Am 14.07.2015 um 12:54 schrieb Chris Packham:
> In commit a18a477 (MIPS: use common code from lib/time.c) MIPS platforms
> started using common the common timer functions which are based around
> the fact that many platforms have a 32-bit free running counter register
> that can be used see commit 8dfafdd (Introduce common timer functions).
>
> Even MIPS64 has such a 32-bit register (some have an additional 64-bit free
> running counter, but that's something for another time).
>
> The problem is that in __read_32bit_c0_register() we read the value from
> this register into an _signed_ int and as it's returned up the call
> chain to timer_read_counter() it gets assigned to an unsigned long. On a
> 32-bit system there is no problem. On a 64-bit system odd things happen,
> sign extension seems to kick in and all of a sudden if the counter
> register happens to have the MSb (i.e. the sign bit) set the negative
> int gets sign extended into a very large unsigned long value. This in
> turn throws out things from get_ticks() up.
>
> Update __read_32bit_c0_register() and __read_32bit_c0_ctrl_register() to
> use "unsigned int res;" instead of "int res;". There seems to be little
> reason to treat these register values as signed. They are either
> counters (which by definition are unsigned) or are made up of various
> bit fields to be interpreted as per the CPU datasheet.
>
> Reported-by: Sachin Surendran <sachin.surendran@alliedtelesis.co.nz>
> Signed-off-by: Chris Packham <judge.packham@gmail.com>
>
> ---
>
> Changes in v2:
> - Use Rob's current email address
>
> arch/mips/include/asm/mipsregs.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)

applied to u-boot-mips/next, thanks

--
- Daniel