On Fri, Nov 22, 2013 at 09:36:09AM +0100, Takashi Iwai wrote: > I got kernel WARNINGs frequently on Haswell laptops complaining about > invalid max DP link bw. With drm.debug=0x0e, it turned out that the > obtained DPCD is utterly bogus when it happens: > [drm:intel_dp_get_dpcd], DPCD: 4d 4d 4d 4d 4d 4d 4d 4d 4d 4d 4d 4d 4d 4d 4d > > This seems happening intermittently without plug state changes and > even after the first few reads succeeded. As a workaround, add a > sanity check for such bogus values and retry reading if it hits. > > Signed-off-by: Takashi Iwai <tiwai@xxxxxxx> *insert lament about how hw never fails to disappoint* A few questions: - Has anyone checked whether the same panel (I guess this is about edp) also fails in the same way on other chips? Maybe with a dual gpu solution? - Jesse has a patch somewhere, please test the diff embedded in this bz comment: https://bugs.freedesktop.org/show_bug.cgi?id=67245#c29 Could be that we have an issue with the panel power timings. - Shouldn't we instead clamp the values read from dpcd to a sane range? Worst case we'll do a few bogus link training rounds ... Also we really should be extracting this stuff from drivers into common code. Somewhen next century maybe ;-) Cheers, Daniel > --- > > drivers/gpu/drm/i915/intel_dp.c | 15 ++++++++++++++- > 1 file changed, 14 insertions(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c > index eb8139da9763..f596353da557 100644 > --- a/drivers/gpu/drm/i915/intel_dp.c > +++ b/drivers/gpu/drm/i915/intel_dp.c > @@ -2792,13 +2792,26 @@ intel_dp_get_dpcd(struct intel_dp *intel_dp) > struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp); > struct drm_device *dev = dig_port->base.base.dev; > struct drm_i915_private *dev_priv = dev->dev_private; > - > + int retry = 0; > char dpcd_hex_dump[sizeof(intel_dp->dpcd) * 3]; > > + again: > if (intel_dp_aux_native_read_retry(intel_dp, 0x000, intel_dp->dpcd, > sizeof(intel_dp->dpcd)) == 0) > return false; /* aux transfer failed */ > > + /* sanity check: sometimes DPCD contains a series of same bogus value > + * even though the above returned success. Retry reading in that case. > + */ > + if (intel_dp->dpcd[0]) { > + int i; > + for (i = 1; i < sizeof(intel_dp->dpcd); i++) > + if (intel_dp->dpcd[i] != intel_dp->dpcd[0]) > + break; > + if (i >= sizeof(intel_dp->dpcd) && retry++ < 2) > + goto again; > + } > + > hex_dump_to_buffer(intel_dp->dpcd, sizeof(intel_dp->dpcd), > 32, 1, dpcd_hex_dump, sizeof(dpcd_hex_dump), false); > DRM_DEBUG_KMS("DPCD: %s\n", dpcd_hex_dump); > -- > 1.8.4.3 > > _______________________________________________ > Intel-gfx mailing list > Intel-gfx@xxxxxxxxxxxxxxxxxxxxx > http://lists.freedesktop.org/mailman/listinfo/intel-gfx -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
