remoteproc: pru: Fix and cleanup firmware interrupt mapping logic

The PRU firmware interrupt mappings are configured and unconfigured in
.start() and .stop() callbacks respectively using the variables 'evt_count'
and a 'mapped_irq' pointer. These variables are modified only during these
callbacks but are not re-initialized/reset properly during unwind or
failure paths. These stale values caused a kernel crash while stopping a
PRU remoteproc running a different firmware with no events on a subsequent
run after a previous run that was running a firmware with events.

Fix this crash by ensuring that the evt_count is 0 and the mapped_irq
pointer is set to NULL in pru_dispose_irq_mapping(). Also, reset these
variables properly during any failures in the .start() callback. While
at this, the pru_dispose_irq_mapping() callsites are all made to look
the same, moving any conditional logic to inside the function.

Reviewed-by: Mathieu Poirier <[e-mail]>
Fixes: c75c9fdac66e ("remoteproc: pru: Add support for PRU specific interrupt configuration")
Reported-by: Vignesh Raghavendra <[e-mail]>
Signed-off-by: Suman Anna <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Bjorn Andersson <[e-mail]>

drivers/remoteproc/pru_rproc.c

···
 
 static void pru_dispose_irq_mapping(struct pru_rproc *pru)
 {
-	while (pru->evt_count--) {
+	if (!pru->mapped_irq)
+		return;
+
+	while (pru->evt_count) {
+		pru->evt_count--;
 		if (pru->mapped_irq[pru->evt_count] > 0)
 			irq_dispose_mapping(pru->mapped_irq[pru->evt_count]);
 	}
 
 	kfree(pru->mapped_irq);
+	pru->mapped_irq = NULL;
 }
 
 /*
···
 	pru->evt_count = rsc->num_evts;
 	pru->mapped_irq = kcalloc(pru->evt_count, sizeof(unsigned int),
 				  GFP_KERNEL);
-	if (!pru->mapped_irq)
+	if (!pru->mapped_irq) {
+		pru->evt_count = 0;
 		return -ENOMEM;
+	}
 
 	/*
 	 * parse and fill in system event to interrupt channel and
···
 	 * corresponding sibling PRUSS INTC node.
 	 */
 	parent = of_get_parent(dev_of_node(pru->dev));
-	if (!parent)
+	if (!parent) {
+		kfree(pru->mapped_irq);
+		pru->mapped_irq = NULL;
+		pru->evt_count = 0;
 		return -ENODEV;
+	}
 
 	irq_parent = of_get_child_by_name(parent, "interrupt-controller");
 	of_node_put(parent);
 	if (!irq_parent) {
 		kfree(pru->mapped_irq);
+		pru->mapped_irq = NULL;
+		pru->evt_count = 0;
 		return -ENODEV;
 	}
 
···
 	pru_control_write_reg(pru, PRU_CTRL_CTRL, val);
 
 	/* dispose irq mapping - new firmware can provide new mapping */
-	if (pru->mapped_irq)
-		pru_dispose_irq_mapping(pru);
+	pru_dispose_irq_mapping(pru);
 
 	return 0;
 }