On Wed, Feb 15, 2023 at 03:15:41PM +0200, Jani Nikula wrote:
> 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. ;)
memcmp_len_reverse()?
>
>
> 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
--
Ville Syrjälä
Intel
