gpu: host1x: Forbid unrelated SETCLASS opcode in the firewall

Several channels could be made to write the same unit concurrently via
the SETCLASS opcode, trusting userspace is a bad idea. It should be
possible to drop the per-client channel reservation and add a per-unit
locking by inserting MLOCK's to the command stream to re-allow the
SETCLASS opcode, but it will be much more work. Let's forbid the
unit-unrelated class changes for now.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Reviewed-by: Erik Faye-Lund <kusmabite@gmail.com>
Reviewed-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

include/linux/host1x.h

@@ -251,6 +251,9 @@ struct host1x_job {
 	/* Check if register is marked as an address reg */
 	int (*is_addr_reg)(struct device *dev, u32 reg, u32 class);
 
+	/* Check if class belongs to the unit */
+	int (*is_valid_class)(u32 class);
+
 	/* Request a SETCLASS to this class */
 	u32 class;