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.
Arguably part of the reason for big dumps is that we use MAX_ELD_BYTES
for the size instead of drm_eld_size(). Granted, using drm_eld_size()
brings other complications, so maybe this is better anyway.
> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/i915/display/intel_display.c | 23 ++++++++++++++++++++
> 1 file changed, 23 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 3479125fbda6..d73aea9040e0 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -5348,6 +5348,23 @@ pipe_config_dp_vsc_sdp_mismatch(struct drm_i915_private *dev_priv,
> }
> }
>
> +/*
> + * Like a revese memcmp(), but returns the
> + * position of the last differing byte.
> + */
> +static int
> +memcmp_pos_reverse(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;
> + }
> +
> + return len;
> +}
Maybe make the function return "length of differing prefix" instead?
If the buffers are identical, you now return len, and the caller dumps
len + 1, overflowing the buffer. This shouldn't happen, because we've
checked before that the buffers do differ, but it's a trap for anyone
who just picks this up for some other use case.
The fix is simple, return "i + 1" if there's a difference, return 0 at
the end if there's not, and drop the + 1 from the caller side.
Renaming the function is the hard part. ;)
BR,
Jani.
> +
> static void
> pipe_config_buffer_mismatch(struct drm_i915_private *dev_priv,
> bool fastset, const char *name,
> @@ -5357,6 +5374,9 @@ 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_pos_reverse(a, b, len) + 1;
> +
> drm_dbg_kms(&dev_priv->drm,
> "fastset mismatch in %s buffer\n", name);
> print_hex_dump(KERN_DEBUG, "expected: ", DUMP_PREFIX_NONE,
> @@ -5364,6 +5384,9 @@ 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_pos_reverse(a, b, len) + 1;
> +
> 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
