On Mon, Apr 16, 2018 at 06:53:09PM +0300, Imre Deak wrote: > LSPCON adapters in low-power state may ignore the first I2C write during > TMDS output buffer enabling, resulting in a blank screen even with an > otherwise enabled pipe. Fix this by reading back and validating the > written value a few times. > > The problem was noticed on GLK machines with an onboard LSPCON adapter > after entering/exiting DC5 power state. Doing an I2C read of the adapter > ID as the first transaction - instead of the I2C write to enable the > TMDS buffers - returns the correct value. Based on this we assume that > the transaction itself is sent properly, it's only the adapter that is > not ready for some reason to accept this first write after waking from > low-power state. In my case the second I2C write attempt always > succeeded. Yeah, I guess this is an OK approach. Probably not much point in optimizing the non-LSPCON case since this is modeset stuff, although we do have the adaptor type passed in so we could if we wanted to. Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105854 > Cc: Clinton Taylor <clinton.a.taylor@xxxxxxxxx> > Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > Signed-off-by: Imre Deak <imre.deak@xxxxxxxxx> > --- > drivers/gpu/drm/drm_dp_dual_mode_helper.c | 39 +++++++++++++++++++++++++------ > 1 file changed, 32 insertions(+), 7 deletions(-) > > diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c b/drivers/gpu/drm/drm_dp_dual_mode_helper.c > index 02a50929af67..e7f4fe2848a5 100644 > --- a/drivers/gpu/drm/drm_dp_dual_mode_helper.c > +++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c > @@ -350,19 +350,44 @@ int drm_dp_dual_mode_set_tmds_output(enum drm_dp_dual_mode_type type, > { > uint8_t tmds_oen = enable ? 0 : DP_DUAL_MODE_TMDS_DISABLE; > ssize_t ret; > + int retry; > > if (type < DRM_DP_DUAL_MODE_TYPE2_DVI) > return 0; > > - ret = drm_dp_dual_mode_write(adapter, DP_DUAL_MODE_TMDS_OEN, > - &tmds_oen, sizeof(tmds_oen)); > - if (ret) { > - DRM_DEBUG_KMS("Failed to %s TMDS output buffers\n", > - enable ? "enable" : "disable"); > - return ret; > + /* > + * LSPCON adapters in low-power state may ignore the first write, so > + * read back and verify the written value a few times. > + */ > + for (retry = 0; retry < 3; retry++) { > + uint8_t tmp; > + > + ret = drm_dp_dual_mode_write(adapter, DP_DUAL_MODE_TMDS_OEN, > + &tmds_oen, sizeof(tmds_oen)); > + if (ret) { > + DRM_DEBUG_KMS("Failed to %s TMDS output buffers (%d attempts)\n", > + enable ? "enable" : "disable", > + retry + 1); > + return ret; > + } > + > + ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_TMDS_OEN, > + &tmp, sizeof(tmp)); > + if (ret) { > + DRM_DEBUG_KMS("I2C read failed during TMDS output buffer %s (%d attempts)\n", > + enable ? "enabling" : "disabling", > + retry + 1); > + return ret; > + } > + > + if (tmp == tmds_oen) > + return 0; > } > > - return 0; > + DRM_DEBUG_KMS("I2C write value mismatch during TMDS output buffer %s\n", > + enable ? "enabling" : "disabling"); > + > + return -EIO; > } > EXPORT_SYMBOL(drm_dp_dual_mode_set_tmds_output); > > -- > 2.13.2 -- Ville Syrjälä Intel _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
