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. 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 _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
