Re: [Intel-gfx] [PATCH v2] drm/i915: Reduce ELD hex dumps a bit

[Jani Nikula <jani.nikula@intel.com>]

On Wed, 15 Feb 2023, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Do the ELD hexdumps only up to the last differing byte.
> The rest is typically all zeroes anyway so not much point
> in dumping it.
>
> Couldn't find anything for memcmp_diff_len() so
> rolled my own.
>
> v2: Use semantics and function name suggested by Jani
>
> Cc: Jani Nikula <jani.nikula@intel.com>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Reviewed-by: Jani Nikula <jani.nikula@intel.com>


> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 3479125fbda6..664322a58236 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -5348,6 +5348,20 @@ pipe_config_dp_vsc_sdp_mismatch(struct drm_i915_private *dev_priv,
>  	}
>  }
>  
> +/* Returns the length up to and including the last differing byte */
> +static size_t
> +memcmp_diff_len(const u8 *a, const u8 *b, size_t len)
> +{
> +	int i;
> +
> +	for (i = len - 1; i >= 0; i--) {
> +		if (a[i] != b[i])
> +			return i + 1;
> +	}
> +
> +	return 0;
> +}
> +
>  static void
>  pipe_config_buffer_mismatch(struct drm_i915_private *dev_priv,
>  			    bool fastset, const char *name,
> @@ -5357,6 +5371,9 @@ pipe_config_buffer_mismatch(struct drm_i915_private *dev_priv,
>  		if (!drm_debug_enabled(DRM_UT_KMS))
>  			return;
>  
> +		/* only dump up to the last difference */
> +		len = memcmp_diff_len(a, b, len);
> +
>  		drm_dbg_kms(&dev_priv->drm,
>  			    "fastset mismatch in %s buffer\n", name);
>  		print_hex_dump(KERN_DEBUG, "expected: ", DUMP_PREFIX_NONE,
> @@ -5364,6 +5381,9 @@ pipe_config_buffer_mismatch(struct drm_i915_private *dev_priv,
>  		print_hex_dump(KERN_DEBUG, "found: ", DUMP_PREFIX_NONE,
>  			       16, 0, b, len, false);
>  	} else {
> +		/* only dump up to the last difference */
> +		len = memcmp_diff_len(a, b, len);
> +
>  		drm_err(&dev_priv->drm, "mismatch in %s buffer\n", name);
>  		print_hex_dump(KERN_ERR, "expected: ", DUMP_PREFIX_NONE,
>  			       16, 0, a, len, false);

-- 
Jani Nikula, Intel Open Source Graphics Center