From 0776a269d725e6ce17ae5ea033e1925be861e2f1 Mon Sep 17 00:00:00 2001 From: Tomi Valkeinen Date: Tue, 28 May 2019 11:27:37 +0300 Subject: drm/bridge: tc358767: use more reliable seq when finishing LT At the end of the link training, two steps have to be taken: 1) tc358767's LT mode is disabled by a write to DP0_SRCCTRL, and 2) Remove LT flag in DPCD 0x102. Toshiba's documentation tells to first write the DPCD, then modify DP0_SRCCTRL. In my testing this often causes issues, and the link disconnects right after those steps. If I reverse the steps, it works every time. There's a chance that this is DP sink specific, though, but as my testing shows this sequence to be much more reliable, let's change it. Signed-off-by: Tomi Valkeinen Reviewed-by: Andrzej Hajda Signed-off-by: Andrzej Hajda Link: https://patchwork.freedesktop.org/patch/msgid/20190528082747.3631-15-tomi.valkeinen@ti.com --- drivers/gpu/drm/bridge/tc358767.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c index a60a2e65e468..40f3efcade50 100644 --- a/drivers/gpu/drm/bridge/tc358767.c +++ b/drivers/gpu/drm/bridge/tc358767.c @@ -961,6 +961,18 @@ static int tc_main_link_enable(struct tc_data *tc) if (ret) goto err; + /* + * Toshiba's documentation suggests to first clear DPCD 0x102, then + * clear the training pattern bit in DP0_SRCCTRL. Testing shows + * that the link sometimes drops if those steps are done in that order, + * but if the steps are done in reverse order, the link stays up. + * + * So we do the steps differently than documented here. + */ + + /* Clear Training Pattern, set AutoCorrect Mode = 1 */ + tc_write(DP0_SRCCTRL, tc_srcctrl(tc) | DP0_SRCCTRL_AUTOCORRECT); + /* Clear DPCD 0x102 */ /* Note: Can Not use DP0_SNKLTCTRL (0x06E4) short cut */ tmp[0] = tc->link.scrambler_dis ? DP_LINK_SCRAMBLING_DISABLE : 0x00; @@ -968,9 +980,6 @@ static int tc_main_link_enable(struct tc_data *tc) if (ret < 0) goto err_dpcd_write; - /* Clear Training Pattern, set AutoCorrect Mode = 1 */ - tc_write(DP0_SRCCTRL, tc_srcctrl(tc) | DP0_SRCCTRL_AUTOCORRECT); - /* Wait */ timeout = 100; do { -- cgit v1.2.3