soc: ti: wkup_m3_ipc: Fix race condition with rproc_boot

Any user of wkup_m3_ipc calls wkup_m3_ipc_get to get a handle and this
checks the value of the static variable m3_ipc_state to see if the
wkup_m3 is ready. Currently this is populated during probe before
rproc_boot has been called, meaning there is a window of time that
wkup_m3_ipc_get can return a valid handle but the wkup_m3 itself is not
ready, leading to invalid IPC calls to the wkup_m3 and system
instability.

To avoid this, move the population of the m3_ipc_state variable until
after rproc_boot has succeeded to guarantee a valid and usable handle
is always returned.

Reported-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
Acked-by: Santosh Shilimkar <ssantosh@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>

drivers/soc/ti/wkup_m3_ipc.c

@@ -419,6 +419,8 @@ static void wkup_m3_rproc_boot_thread(struct wkup_m3_ipc *m3_ipc)
 	ret = rproc_boot(m3_ipc->rproc);
 	if (ret)
 		dev_err(dev, "rproc_boot failed\n");
+	else
+		m3_ipc_state = m3_ipc;
 
 	do_exit(0);
 }
@@ -505,8 +507,6 @@ static int wkup_m3_ipc_probe(struct platform_device *pdev)
 		goto err_put_rproc;
 	}
 
-	m3_ipc_state = m3_ipc;
-
 	return 0;
 
 err_put_rproc: