linux-kernel - [PATCH 18/20] drm/bridge: tc358775: fix the power-up/down delays

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Message-Id: <20240506-tc358775-fix-powerup-v1-18-545dcf00b8dd@kernel.org>
Date: Mon, 06 May 2024 15:34:47 +0200
From: Michael Walle <mwalle@...nel.org>
To: Andrzej Hajda <andrzej.hajda@...el.com>, 
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, 
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
 Chun-Kuang Hu <chunkuang.hu@...nel.org>, 
 Philipp Zabel <p.zabel@...gutronix.de>, 
 Matthias Brugger <matthias.bgg@...il.com>, 
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, 
 Sam Ravnborg <sam@...nborg.org>, Vinay Simha BN <simhavcs@...il.com>, 
 Tony Lindgren <tony@...mide.com>
Cc: Daniel Semkowicz <dse@...umatec.com>, dri-devel@...ts.freedesktop.org, 
 linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org, 
 linux-arm-kernel@...ts.infradead.org, Michael Walle <mwalle@...nel.org>
Subject: [PATCH 18/20] drm/bridge: tc358775: fix the power-up/down delays

Implement the delays according to Figure 8-10 and 8-11 of the datasheet.
In particular, the datasheet states that the *maximum* time between
enabling the VDDIO and VDD is 10ms. Currently, as implemented this is
always violated. Of course, this is only a best effort because we cannot
be sure enabling of the two regulators will be that fast.
The time between releasing the stby GPIO and releasing the reset GPIO
must be at least 10us and not 10ms as it was before this patch. After
reset is released, there must be at least a delay of 200us until the
first HS clock is received.

Signed-off-by: Michael Walle <mwalle@...nel.org>
---
 drivers/gpu/drm/bridge/tc358775.c | 9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

diff --git a/drivers/gpu/drm/bridge/tc358775.c b/drivers/gpu/drm/bridge/tc358775.c
index d5b3d691d2c1..99dbbb1fee78 100644
--- a/drivers/gpu/drm/bridge/tc358775.c
+++ b/drivers/gpu/drm/bridge/tc358775.c
@@ -242,18 +242,16 @@ static void tc358775_power_up(struct tc_data *tc)
 	ret = regulator_enable(tc->vddio);
 	if (ret < 0)
 		dev_err(dev, "regulator vddio enable failed, %d\n", ret);
-	usleep_range(10000, 11000);
 
 	ret = regulator_enable(tc->vdd);
 	if (ret < 0)
 		dev_err(dev, "regulator vdd enable failed, %d\n", ret);
-	usleep_range(10000, 11000);
 
 	gpiod_set_value(tc->stby_gpio, 0);
-	usleep_range(10000, 11000);
+	usleep_range(10, 20);
 
 	gpiod_set_value(tc->reset_gpio, 0);
-	usleep_range(10, 20);
+	usleep_range(200, 250);
 }
 
 static void tc358775_power_down(struct tc_data *tc)
@@ -265,17 +263,14 @@ static void tc358775_power_down(struct tc_data *tc)
 	usleep_range(10, 20);
 
 	gpiod_set_value(tc->stby_gpio, 1);
-	usleep_range(10000, 11000);
 
 	ret = regulator_disable(tc->vdd);
 	if (ret < 0)
 		dev_err(dev, "regulator vdd disable failed, %d\n", ret);
-	usleep_range(10000, 11000);
 
 	ret = regulator_disable(tc->vddio);
 	if (ret < 0)
 		dev_err(dev, "regulator vddio disable failed, %d\n", ret);
-	usleep_range(10000, 11000);
 }
 
 static void tc_bridge_pre_enable(struct drm_bridge *bridge)

-- 
2.39.2