@@ -319,7 +319,6 @@ static int cafe_smbus_write_data(struct cafe_camera *cam,
{
unsigned int rval;
unsigned long flags;
- DEFINE_WAIT(the_wait);
spin_lock_irqsave(&cam->dev_lock, flags);
rval = TWSIC0_EN | ((addr << TWSIC0_SID_SHIFT) & TWSIC0_SID);
@@ -334,28 +333,27 @@ static int cafe_smbus_write_data(struct cafe_camera *cam,
cafe_reg_write(cam, REG_TWSIC1, rval);
spin_unlock_irqrestore(&cam->dev_lock, flags);
+ /* Unfortunately, reading TWSIC1 too soon after sending a command
+ * causes the device to die.
+ * Use a busy-wait because we often send a large quantity of small
+ * commands at-once; using msleep() would cause a lot of context
+ * switches which take longer than 2ms, resulting in a noticable
+ * boot-time and capture-start delays.
+ */
+ mdelay(2);
+
/*
- * Time to wait for the write to complete. THIS IS A RACY
- * WAY TO DO IT, but the sad fact is that reading the TWSIC1
- * register too quickly after starting the operation sends
- * the device into a place that may be kinder and better, but
- * which is absolutely useless for controlling the sensor. In
- * practice we have plenty of time to get into our sleep state
- * before the interrupt hits, and the worst case is that we
- * time out and then see that things completed, so this seems
- * the best way for now.
+ * Another sad fact is that sometimes, commands silently complete but
+ * cafe_smbus_write_done() never becomes aware of this.
+ * This happens at random and appears to possible occur with any
+ * command.
+ * We don't understand why this is. We work around this issue
+ * with the timeout in the wait below, assuming that all commands
+ * complete within the timeout.
*/
- do {
- prepare_to_wait(&cam->smbus_wait, &the_wait,
- TASK_UNINTERRUPTIBLE);
- schedule_timeout(1); /* even 1 jiffy is too long */
- finish_wait(&cam->smbus_wait, &the_wait);
- } while (!cafe_smbus_write_done(cam));
-
-#ifdef IF_THE_CAFE_HARDWARE_WORKED_RIGHT
wait_event_timeout(cam->smbus_wait, cafe_smbus_write_done(cam),
CAFE_SMBUS_TIMEOUT);
-#endif
+
spin_lock_irqsave(&cam->dev_lock, flags);
rval = cafe_reg_read(cam, REG_TWSIC1);
spin_unlock_irqrestore(&cam->dev_lock, flags);