misc: fastrpc: do not interrupt kernel calls

the DSP firmware requires some calls to be held until processing has
completed: this is to guarantee that memory continues to be
accessible.

Nevertheless, the fastrpc driver chooses not support the case were
requests need to be held for unbounded amounts of time. If such a
use-case becomes necessary, this timeout will need to be revisited.
Signed-off-by: Jorge Ramirez-Ortiz <jorge.ramirez-ortiz@linaro.org>
Reviewed-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20191009144123.24583-4-srinivas.kandagatla@linaro.orgSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/fastrpc.c

@@ -959,8 +959,13 @@ static int fastrpc_internal_invoke(struct fastrpc_user *fl,  u32 kernel,
 	if (err)
 		goto bail;
 
-	/* Wait for remote dsp to respond or time out */
+	if (kernel) {
+		if (!wait_for_completion_timeout(&ctx->work, 10 * HZ))
+			err = -ETIMEDOUT;
+	} else {
 		err = wait_for_completion_interruptible(&ctx->work);
+	}
+
 	if (err)
 		goto bail;