On Wed, 15 Feb 2023, Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx> wrote:
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> 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@xxxxxxxxx>
> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Reviewed-by: Jani Nikula <jani.nikula@xxxxxxxxx>
> ---
> 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
