[Intel-gfx] [PATCH] drm/i915/selftests: Fix compare functions provided for sorting

[Chris Wilson]

Quoting Sudeep Holla (2020-07-09 16:49:31)
> Both cmp_u32 and cmp_u64 are comparing the pointers instead of the value
> at those pointers. This will result in incorrect/unsorted list. Fix it
> by deferencing the pointers before comparison.
> 
> Cc: Chris Wilson <chris at chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuoppala at linux.intel.com>
> Signed-off-by: Sudeep Holla <sudeep.holla at arm.com>
> ---
>  drivers/gpu/drm/i915/gt/selftest_rps.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> Hi,
> 
> I am not sure if I can put 2 fixes tags, but these are the ones affected.
> 
> Fixes: 4ba74e53ada3 ("drm/i915/selftests: Verify frequency scaling with RPS")
> Fixes: 8757797ff9c9 ("drm/i915/selftests: Repeat the rps clock frequency measurement")

Might as well tag the fixes, just in case anyone wants to use the tests.
 
> I made similar mistake and after I fixed it, just looked if there are any
> similar bugs and found this.
> 
> Regards,
> Sudeep
> 
> diff --git a/drivers/gpu/drm/i915/gt/selftest_rps.c b/drivers/gpu/drm/i915/gt/selftest_rps.c
> index 5049c3dd08a6..c91981e75ebf 100644
> --- a/drivers/gpu/drm/i915/gt/selftest_rps.c
> +++ b/drivers/gpu/drm/i915/gt/selftest_rps.c
> @@ -44,9 +44,9 @@ static int cmp_u64(const void *A, const void *B)
>  {
>         const u64 *a = A, *b = B;
>  
> -       if (a < b)
> +       if (*a < *b)
>                 return -1;
> -       else if (a > b)
> +       else if (*a > *b)
>                 return 1;

Oh my golly gosh.

Thanks, thanks and thrice thanks.
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>

I better double check all my qsort-compare funcs for similar brianfarts.
-Chris