Re: [igt-dev] [PATCH i-g-t 1/3] lib/debugfs: Fix wraparound handling for crc frame counter check

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Nov 06, 2018 at 06:19:41PM +0200, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> Deal with frame counter wraparound correcrtly.
> 
> Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> ---
>  lib/igt_debugfs.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/lib/igt_debugfs.c b/lib/igt_debugfs.c
> index a3aca8466658..70874416d128 100644
> --- a/lib/igt_debugfs.c
> +++ b/lib/igt_debugfs.c
> @@ -975,6 +975,16 @@ void igt_pipe_crc_get_single(igt_pipe_crc_t *pipe_crc, igt_crc_t *crc)
>  	crc_sanity_checks(crc);
>  }
>  
> +static bool vbl_after_eq(uint32_t a, uint32_t b)
> +{
> +	return (int32_t)(a - b) >= 0;
> +}
> +
> +static bool vbl_before_eq(uint32_t a, uint32_t b)
> +{
> +	return vbl_after_eq(b, a);
> +}
> +
>  /**
>   * igt_pipe_crc_get_current:
>   * @drm_fd: Pointer to drm fd for vblank counter
> @@ -999,7 +1009,7 @@ igt_pipe_crc_get_current(int drm_fd, igt_pipe_crc_t *pipe_crc, igt_crc_t *crc)
>  			igt_pipe_crc_get_single(pipe_crc, crc);
>  			return;
>  		}
> -	} while (crc->frame <= vblank);
> +	} while (vbl_before_eq(crc->frame, vblank));
>  
>  	crc_sanity_checks(crc);
>  }
> -- 
> 2.18.1
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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