[PATCH 2/2] drm/bridge: ti-sn65dsi83: protect device resources on unplug

[Luca Ceresoli]

To support hot-unplug of this bridge we need to protect access to device
resources in case sn65dsi83_remove() happens concurrently to other code.

Some care is needed for the case when the unplug happens before
sn65dsi83_atomic_disable() has a chance to enter the critical section
(i.e. a successful drm_bridge_enter() call), which occurs whenever the
hardware is removed while the display is active. When that happens,
sn65dsi83_atomic_disable() in unable to release some resources, thus this
needs to be done in sn65dsi83_remove() after drm_bridge_unplug().

Signed-off-by: Luca Ceresoli <luca.ceresoli at bootlin.com>
---
 drivers/gpu/drm/bridge/ti-sn65dsi83.c | 53 +++++++++++++++++++++++++++++++++++
 1 file changed, 53 insertions(+)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
index 033c44326552ab167d4e8d9b74957c585e4c6fb7..9e4cecf4f7cb056f0c34e87007fcebf50780e49c 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
@@ -157,6 +157,7 @@ struct sn65dsi83 {
 	struct drm_bridge		*panel_bridge;
 	struct gpio_desc		*enable_gpio;
 	struct regulator		*vcc;
+	bool				disable_resources_needed;
 	bool				lvds_dual_link;
 	bool				lvds_dual_link_even_odd_swap;
 	int				lvds_vod_swing_conf[2];
@@ -406,6 +407,10 @@ static void sn65dsi83_reset_work(struct work_struct *ws)
 {
 	struct sn65dsi83 *ctx = container_of(ws, struct sn65dsi83, reset_work);
 	int ret;
+	int idx;
+
+	if (!drm_bridge_enter(&ctx->bridge, &idx))
+		return;
 
 	/* Reset the pipe */
 	ret = sn65dsi83_reset_pipe(ctx);
@@ -415,12 +420,18 @@ static void sn65dsi83_reset_work(struct work_struct *ws)
 	}
 	if (ctx->irq)
 		enable_irq(ctx->irq);
+
+	drm_bridge_exit(idx);
 }
 
 static void sn65dsi83_handle_errors(struct sn65dsi83 *ctx)
 {
 	unsigned int irq_stat;
 	int ret;
+	int idx;
+
+	if (!drm_bridge_enter(&ctx->bridge, &idx))
+		return;
 
 	/*
 	 * Schedule a reset in case of:
@@ -441,6 +452,8 @@ static void sn65dsi83_handle_errors(struct sn65dsi83 *ctx)
 
 		schedule_work(&ctx->reset_work);
 	}
+
+	drm_bridge_exit(idx);
 }
 
 static void sn65dsi83_monitor_work(struct work_struct *work)
@@ -478,10 +491,15 @@ static void sn65dsi83_atomic_pre_enable(struct drm_bridge *bridge,
 	__le16 le16val;
 	u16 val;
 	int ret;
+	int idx;
+
+	if (!drm_bridge_enter(bridge, &idx))
+		return;
 
 	ret = regulator_enable(ctx->vcc);
 	if (ret) {
 		dev_err(ctx->dev, "Failed to enable vcc: %d\n", ret);
+		drm_bridge_exit(idx);
 		return;
 	}
 
@@ -625,6 +643,8 @@ static void sn65dsi83_atomic_pre_enable(struct drm_bridge *bridge,
 		dev_err(ctx->dev, "failed to lock PLL, ret=%i\n", ret);
 		/* On failure, disable PLL again and exit. */
 		regmap_write(ctx->regmap, REG_RC_PLL_EN, 0x00);
+		ctx->disable_resources_needed = true;
+		drm_bridge_exit(idx);
 		return;
 	}
 
@@ -633,6 +653,9 @@ static void sn65dsi83_atomic_pre_enable(struct drm_bridge *bridge,
 
 	/* Wait for 10ms after soft reset as specified in datasheet */
 	usleep_range(10000, 12000);
+
+	ctx->disable_resources_needed = true;
+	drm_bridge_exit(idx);
 }
 
 static void sn65dsi83_atomic_enable(struct drm_bridge *bridge,
@@ -640,6 +663,10 @@ static void sn65dsi83_atomic_enable(struct drm_bridge *bridge,
 {
 	struct sn65dsi83 *ctx = bridge_to_sn65dsi83(bridge);
 	unsigned int pval;
+	int idx;
+
+	if (!drm_bridge_enter(bridge, &idx))
+		return;
 
 	/* Clear all errors that got asserted during initialization. */
 	regmap_read(ctx->regmap, REG_IRQ_STAT, &pval);
@@ -659,6 +686,8 @@ static void sn65dsi83_atomic_enable(struct drm_bridge *bridge,
 		/* Use the polling task */
 		sn65dsi83_monitor_start(ctx);
 	}
+
+	drm_bridge_exit(idx);
 }
 
 static void sn65dsi83_atomic_disable(struct drm_bridge *bridge,
@@ -666,6 +695,10 @@ static void sn65dsi83_atomic_disable(struct drm_bridge *bridge,
 {
 	struct sn65dsi83 *ctx = bridge_to_sn65dsi83(bridge);
 	int ret;
+	int idx;
+
+	if (!drm_bridge_enter(bridge, &idx))
+		return;
 
 	if (ctx->irq) {
 		/* Disable irq */
@@ -685,6 +718,9 @@ static void sn65dsi83_atomic_disable(struct drm_bridge *bridge,
 		dev_err(ctx->dev, "Failed to disable vcc: %d\n", ret);
 
 	regcache_mark_dirty(ctx->regmap);
+
+	ctx->disable_resources_needed = false;
+	drm_bridge_exit(idx);
 }
 
 static enum drm_mode_status
@@ -1005,7 +1041,24 @@ static void sn65dsi83_remove(struct i2c_client *client)
 {
 	struct sn65dsi83 *ctx = i2c_get_clientdata(client);
 
+	drm_bridge_unplug(&ctx->bridge);
 	drm_bridge_remove(&ctx->bridge);
+
+	/*
+	 * sn65dsi83_atomic_disable() should release some resources, but it
+	 * cannot if we call drm_bridge_unplug() before it can
+	 * drm_bridge_enter(). If that happens, let's release those
+	 * resources now.
+	 */
+	if (ctx->disable_resources_needed) {
+		if (!ctx->irq)
+			sn65dsi83_monitor_stop(ctx);
+
+		gpiod_set_value_cansleep(ctx->enable_gpio, 0);
+		usleep_range(10000, 11000);
+
+		regulator_disable(ctx->vcc);
+	}
 }
 
 static const struct i2c_device_id sn65dsi83_id[] = {

-- 
2.50.1