[PATCH v3 7/7] drm/bridge: ti-sn65dsi86: Add mystery delay to enable()

[Sean Paul <sean@poorly.run>]

From: Sean Paul <seanpaul@chromium.org>

This patch adds a 70ms mystery delay to the bridge driver in enable.
By experimentation, it seems like it can go anywhere up until we
initiate semi-auto link training. If we don't have the delay, link
training fails.

I tried to root cause this as best I could, but neither the datasheet
for the panel nor the bridge mention a delay of this magnitude in their
timing requirements. So for now, add the mystery delay until someone
figures out a better fix.

Changes in v3:
- Added to the set

Cc: Sandeep Panda <spanda@codeaurora.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
---
 drivers/gpu/drm/bridge/ti-sn65dsi86.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index d3e27e52ea759..f8a931cf3665e 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -458,6 +458,18 @@ static void ti_sn_bridge_enable(struct drm_bridge *bridge)
 	unsigned int val;
 	int ret;
 
+	/*
+	 * FIXME:
+	 * This 70ms was found necessary by experimentation. If it's not
+	 * present, link training fails. It seems like it can go anywhere from
+	 * pre_enable() up to semi-auto link training initiation below.
+	 *
+	 * Neither the datasheet for the bridge nor the panel tested mention a
+	 * delay of this magnitude in the timing requirements. So for now, add
+	 * the mystery delay until someone figures out a better fix.
+	 */
+	msleep(70);
+
 	/* DSI_A lane config */
 	val = CHA_DSI_LANES(4 - pdata->dsi->lanes);
 	regmap_update_bits(pdata->regmap, SN_DSI_LANES_REG,
-- 
Sean Paul, Software Engineer, Google / Chromium OS

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