drm/i2c: tda998x: re-implement "Fix EDID read timeout on HDMI connect"

Commit 6833d26ef823 ("drm: tda998x: Fix EDID read timeout on HDMI
connect") used a weak scheme to try and delay reading EDID on a HDMI
connect event.  It is weak because delaying the notification of a
hotplug event does not stop userspace from trying to read the EDID
within the 100ms delay.

The solution provided here solves this issue:
* When a HDMI connection event is detected, mark a blocking flag for
  EDID reads, and start a timer for the delay.
* If an EDID read is attempted, and the blocking flag is set, wait
  for the blocking flag to clear.
* When the timer expires, clear the blocking flag and wake any thread
  waiting for the EDID read.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 68 insertions, 12 deletions

diff --git a/drivers/gpu/drm/i2c/tda998x_drv.c b/drivers/gpu/drm/i2c/tda998x_drv.c
index ad3ce3479edf..a53696fd8938 100644
--- a/drivers/gpu/drm/i2c/tda998x_drv.c
+++ b/drivers/gpu/drm/i2c/tda998x_drv.c
@@ -34,7 +34,6 @@ struct tda998x_priv {
         struct i2c_client *cec;
         struct i2c_client *hdmi;
         struct mutex mutex;
-        struct delayed_work dwork;
         uint16_t rev;
         uint8_t current_page;
         int dpms;
@@ -47,6 +46,11 @@ struct tda998x_priv {
         wait_queue_head_t wq_edid;
         volatile int wq_edid_wait;
         struct drm_encoder *encoder;
+
+        struct work_struct detect_work;
+        struct timer_list edid_delay_timer;
+        wait_queue_head_t edid_delay_waitq;
+        bool edid_delay_active;
 };
 
 #define to_tda998x_priv(x)  ((struct tda998x_priv *)to_encoder_slave(x)->slave_priv)
@@ -551,15 +555,50 @@ tda998x_reset(struct tda998x_priv *priv)
         reg_write(priv, REG_MUX_VP_VIP_OUT, 0x24);
 }
 
-/* handle HDMI connect/disconnect */
-static void tda998x_hpd(struct work_struct *work)
+/*
+ * The TDA998x has a problem when trying to read the EDID close to a
+ * HPD assertion: it needs a delay of 100ms to avoid timing out while
+ * trying to read EDID data.
+ *
+ * However, tda998x_encoder_get_modes() may be called at any moment
+ * after tda998x_encoder_detect() indicates that we are connected, so
+ * we need to delay probing modes in tda998x_encoder_get_modes() after
+ * we have seen a HPD inactive->active transition.  This code implements
+ * that delay.
+ */
+static void tda998x_edid_delay_done(unsigned long data)
+{
+        struct tda998x_priv *priv = (struct tda998x_priv *)data;
+
+        priv->edid_delay_active = false;
+        wake_up(&priv->edid_delay_waitq);
+        schedule_work(&priv->detect_work);
+}
+
+static void tda998x_edid_delay_start(struct tda998x_priv *priv)
+{
+        priv->edid_delay_active = true;
+        mod_timer(&priv->edid_delay_timer, jiffies + HZ/10);
+}
+
+static int tda998x_edid_delay_wait(struct tda998x_priv *priv)
+{
+        return wait_event_killable(priv->edid_delay_waitq, !priv->edid_delay_active);
+}
+
+/*
+ * We need to run the KMS hotplug event helper outside of our threaded
+ * interrupt routine as this can call back into our get_modes method,
+ * which will want to make use of interrupts.
+ */
+static void tda998x_detect_work(struct work_struct *work)
 {
-        struct delayed_work *dwork = to_delayed_work(work);
         struct tda998x_priv *priv =
-                        container_of(dwork, struct tda998x_priv, dwork);
+                container_of(work, struct tda998x_priv, detect_work);
+        struct drm_device *dev = priv->encoder->dev;
 
-        if (priv->encoder->dev)
-                drm_kms_helper_hotplug_event(priv->encoder->dev);
+        if (dev)
+                drm_kms_helper_hotplug_event(dev);
 }
 
 /*
@@ -585,7 +624,11 @@ static irqreturn_t tda998x_irq_thread(int irq, void *data)
                 wake_up(&priv->wq_edid);
                 handled = true;
         } else if (cec != 0) {                  /* HPD change */
-                schedule_delayed_work(&priv->dwork, HZ/10);
+                if (lvl & CEC_RXSHPDLEV_HPD)
+                        tda998x_edid_delay_start(priv);
+                else
+                        schedule_work(&priv->detect_work);
+
                 handled = true;
         }
         return IRQ_RETVAL(handled);
@@ -1103,6 +1146,14 @@ tda998x_encoder_get_modes(struct tda998x_priv *priv,
         struct edid *edid;
         int n;
 
+        /*
+         * If we get killed while waiting for the HPD timeout, return
+         * no modes found: we are not in a restartable path, so we
+         * can't handle signals gracefully.
+         */
+        if (tda998x_edid_delay_wait(priv))
+                return 0;
+
         if (priv->rev == TDA19988)
                 reg_clear(priv, REG_TX4, TX4_PD_RAM);
 
@@ -1149,10 +1200,12 @@ static void tda998x_destroy(struct tda998x_priv *priv)
         /* disable all IRQs and free the IRQ handler */
         cec_write(priv, REG_CEC_RXSHPDINTENA, 0);
         reg_clear(priv, REG_INT_FLAGS_2, INT_FLAGS_2_EDID_BLK_RD);
-        if (priv->hdmi->irq) {
+
+        if (priv->hdmi->irq)
                 free_irq(priv->hdmi->irq, priv);
-                cancel_delayed_work_sync(&priv->dwork);
-        }
+
+        del_timer_sync(&priv->edid_delay_timer);
+        cancel_work_sync(&priv->detect_work);
 
         i2c_unregister_device(priv->cec);
 }
@@ -1253,6 +1306,10 @@ static int tda998x_create(struct i2c_client *client, struct tda998x_priv *priv)
         priv->dpms = DRM_MODE_DPMS_OFF;
 
         mutex_init(&priv->mutex);       /* protect the page access */
+        init_waitqueue_head(&priv->edid_delay_waitq);
+        setup_timer(&priv->edid_delay_timer, tda998x_edid_delay_done,
+                    (unsigned long)priv);
+        INIT_WORK(&priv->detect_work, tda998x_detect_work);
 
         /* wake up the device: */
         cec_write(priv, REG_CEC_ENAMODS,
@@ -1311,7 +1368,6 @@ static int tda998x_create(struct i2c_client *client, struct tda998x_priv *priv)
 
                 /* init read EDID waitqueue and HDP work */
                 init_waitqueue_head(&priv->wq_edid);
-                INIT_DELAYED_WORK(&priv->dwork, tda998x_hpd);
 
                 /* clear pending interrupts */
                 reg_read(priv, REG_INT_FLAGS_0);