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Commit 0776a269 authored by Tomi Valkeinen's avatar Tomi Valkeinen Committed by Andrzej Hajda
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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: default avatarTomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: default avatarAndrzej Hajda <a.hajda@samsung.com>
Signed-off-by: default avatarAndrzej Hajda <a.hajda@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190528082747.3631-15-tomi.valkeinen@ti.com
parent 31b4c884

drivers/gpu/drm/bridge/tc358767.c

+12 −3
Original line number Diff line number Diff line
@@ -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 {