Input: wm831x-ts - fix races with IRQ management

If the WM831x pen down and data IRQs run in parallel it is possible for the
data and pen down IRQs to deadlock themselves as one is part way through
disabling its operation while the other is part way through enabling. Fix
this by always disabling the pen down interrupt while data is active and
vice versa. When a changeover is required we disable the IRQ that is to
be stopped then schedule work that will enable the new IRQ.

We need to handle the data flow in the data IRQ as the readback from the
device needs to be ordered correctly with the IRQ for robust operation.

This also fixes an issue when using the built in IRQs due to enable_irq()
not being valid from interrupt context on an interrupt controller with bus
operations like the built in IRQ controller - this issue may also have
affected other interrupt controllers. We can't rely on having the data
and pen down IRQs available via GPIOs on the CPU on every system.

Signed-off-by: Mark Brown <[e-mail]>
Signed-off-by: Dmitry Torokhov <[e-mail]>

drivers/input/touchscreen/wm831x-ts.c

···
 	unsigned int pd_irq;
 	bool pressure;
 	bool pen_down;
+	struct work_struct pd_data_work;
 };
+
+static void wm831x_pd_data_work(struct work_struct *work)
+{
+	struct wm831x_ts *wm831x_ts =
+		container_of(work, struct wm831x_ts, pd_data_work);
+
+	if (wm831x_ts->pen_down) {
+		enable_irq(wm831x_ts->data_irq);
+		dev_dbg(wm831x_ts->wm831x->dev, "IRQ PD->DATA done\n");
+	} else {
+		enable_irq(wm831x_ts->pd_irq);
+		dev_dbg(wm831x_ts->wm831x->dev, "IRQ DATA->PD done\n");
+	}
+}
 
 static irqreturn_t wm831x_ts_data_irq(int irq, void *irq_data)
 {
···
 	}
 
 	if (!wm831x_ts->pen_down) {
+		/* Switch from data to pen down */
+		dev_dbg(wm831x->dev, "IRQ DATA->PD\n");
+
 		disable_irq_nosync(wm831x_ts->data_irq);
 
 		/* Don't need data any more */
···
 					 ABS_PRESSURE, 0);
 
 		input_report_key(wm831x_ts->input_dev, BTN_TOUCH, 0);
+
+		schedule_work(&wm831x_ts->pd_data_work);
 	}
 
 	input_sync(wm831x_ts->input_dev);
···
 	struct wm831x_ts *wm831x_ts = irq_data;
 	struct wm831x *wm831x = wm831x_ts->wm831x;
 	int ena = 0;
+
+	if (wm831x_ts->pen_down)
+		return IRQ_HANDLED;
+
+	disable_irq_nosync(wm831x_ts->pd_irq);
 
 	/* Start collecting data */
 	if (wm831x_ts->pressure)
···
 			WM831X_TCHPD_EINT, WM831X_TCHPD_EINT);
 
 	wm831x_ts->pen_down = true;
-	enable_irq(wm831x_ts->data_irq);
+
+	/* Switch from pen down to data */
+	dev_dbg(wm831x->dev, "IRQ PD->DATA\n");
+	schedule_work(&wm831x_ts->pd_data_work);
 
 	return IRQ_HANDLED;
 }
···
 	struct wm831x_ts *wm831x_ts = input_get_drvdata(idev);
 	struct wm831x *wm831x = wm831x_ts->wm831x;
 
+	/* Shut the controller down, disabling all other functionality too */
 	wm831x_set_bits(wm831x, WM831X_TOUCH_CONTROL_1,
-			WM831X_TCH_ENA | WM831X_TCH_CVT_ENA |
-			WM831X_TCH_X_ENA | WM831X_TCH_Y_ENA |
-			WM831X_TCH_Z_ENA, 0);
+			WM831X_TCH_ENA | WM831X_TCH_X_ENA |
+			WM831X_TCH_Y_ENA | WM831X_TCH_Z_ENA, 0);
 
-	if (wm831x_ts->pen_down)
+	/* Make sure any pending IRQs are done, the above will prevent
+	 * new ones firing.
+	 */
+	synchronize_irq(wm831x_ts->data_irq);
+	synchronize_irq(wm831x_ts->pd_irq);
+
+	/* Make sure the IRQ completion work is quiesced */
+	flush_work_sync(&wm831x_ts->pd_data_work);
+
+	/* If we ended up with the pen down then make sure we revert back
+	 * to pen detection state for the next time we start up.
+	 */
+	if (wm831x_ts->pen_down) {
 		disable_irq(wm831x_ts->data_irq);
+		enable_irq(wm831x_ts->pd_irq);
+		wm831x_ts->pen_down = false;
+	}
 }
 
 static __devinit int wm831x_ts_probe(struct platform_device *pdev)
···
 
 	wm831x_ts->wm831x = wm831x;
 	wm831x_ts->input_dev = input_dev;
+	INIT_WORK(&wm831x_ts->pd_data_work, wm831x_pd_data_work);
 
 	/*
 	 * If we have a direct IRQ use it, otherwise use the interrupt