linux-kernel - [RFC PATCH 2/3] drm/bridge: ti-sn65dsi83: Fix enable/disable flow to meet spec

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Message-Id: <20230418104242.877897-1-frieder@fris.de>
Date:   Tue, 18 Apr 2023 12:42:41 +0200
From:   Frieder Schrempf <frieder@...s.de>
To:     Andrzej Hajda <andrzej.hajda@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        David Airlie <airlied@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Robert Foss <rfoss@...nel.org>
Cc:     Frieder Schrempf <frieder.schrempf@...tron.de>,
        Alexander Stein <alexander.stein@...tq-group.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Jonas Karlman <jonas@...boo.se>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Marek Vasut <marex@...x.de>, Sam Ravnborg <sam@...nborg.org>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Ville Syrjälä 
        <ville.syrjala@...ux.intel.com>
Subject: [RFC PATCH 2/3] drm/bridge: ti-sn65dsi83: Fix enable/disable flow to meet spec

From: Frieder Schrempf <frieder.schrempf@...tron.de>

The datasheet describes the following initialization flow including
minimum delay times between each step:

1. DSI data lanes need to be in LP-11 and the clock lane in HS mode
2. toggle EN signal
3. initialize registers
4. enable PLL
5. soft reset
6. enable DSI stream
7. check error status register

To meet this requirement we need to make sure the host bridge's
pre_enable() is called first by using the pre_enable_prev_first
flag.

Furthermore we need to split enable() into pre_enable() which covers
steps 2-5 from above and enable() which covers step 7 and is called
after the host bridge's enable().

Signed-off-by: Frieder Schrempf <frieder.schrempf@...tron.de>
---
 drivers/gpu/drm/bridge/ti-sn65dsi83.c | 19 ++++++++++++++++---
 1 file changed, 16 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
index 75286c9afbb9..a82f10b8109f 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
@@ -321,8 +321,8 @@ static u8 sn65dsi83_get_dsi_div(struct sn65dsi83 *ctx)
 	return dsi_div - 1;
 }
 
-static void sn65dsi83_atomic_enable(struct drm_bridge *bridge,
-				    struct drm_bridge_state *old_bridge_state)
+static void sn65dsi83_atomic_pre_enable(struct drm_bridge *bridge,
+					struct drm_bridge_state *old_bridge_state)
 {
 	struct sn65dsi83 *ctx = bridge_to_sn65dsi83(bridge);
 	struct drm_atomic_state *state = old_bridge_state->base.state;
@@ -484,11 +484,22 @@ static void sn65dsi83_atomic_enable(struct drm_bridge *bridge,
 	/* Trigger reset after CSR register update. */
 	regmap_write(ctx->regmap, REG_RC_RESET, REG_RC_RESET_SOFT_RESET);
 
+	/* Wait for 10ms after soft reset as specified in datasheet */
+	usleep_range(10000, 12000);
+}
+
+static void sn65dsi83_atomic_enable(struct drm_bridge *bridge,
+				    struct drm_bridge_state *old_bridge_state)
+{
+	struct sn65dsi83 *ctx = bridge_to_sn65dsi83(bridge);
+	unsigned int pval;
+
 	/* Clear all errors that got asserted during initialization. */
 	regmap_read(ctx->regmap, REG_IRQ_STAT, &pval);
 	regmap_write(ctx->regmap, REG_IRQ_STAT, pval);
 
-	usleep_range(10000, 12000);
+	/* Wait for 1ms and check for errors in status register */
+	usleep_range(1000, 1100);
 	regmap_read(ctx->regmap, REG_IRQ_STAT, &pval);
 	if (pval)
 		dev_err(ctx->dev, "Unexpected link status 0x%02x\n", pval);
@@ -555,6 +566,7 @@ static const struct drm_bridge_funcs sn65dsi83_funcs = {
 	.attach			= sn65dsi83_attach,
 	.detach			= sn65dsi83_detach,
 	.atomic_enable		= sn65dsi83_atomic_enable,
+	.atomic_pre_enable	= sn65dsi83_atomic_pre_enable,
 	.atomic_disable		= sn65dsi83_atomic_disable,
 	.mode_valid		= sn65dsi83_mode_valid,
 
@@ -697,6 +709,7 @@ static int sn65dsi83_probe(struct i2c_client *client)
 
 	ctx->bridge.funcs = &sn65dsi83_funcs;
 	ctx->bridge.of_node = dev->of_node;
+	ctx->bridge.pre_enable_prev_first = true;
 	drm_bridge_add(&ctx->bridge);
 
 	ret = sn65dsi83_host_attach(ctx);
-- 
2.40.0