drm/i915/dkl: return if tc_port is invalid in dkl_phy_set_hip_idx()

In dkl_phy_set_hip_idx(), we may try to shift a value negatively,
whose behavior is undefined.  This can happen because we define
TC_PORT_NONE to -1, so theoretically tc_port could be -1.  We will
then use tc_port to shift to the correct address of the specified
port, but if it's negative, anything can happen.

If this happens or tc_port exceeds I915_MAX_TC_PORTS, it's safer to
return with a warning than risk an invalid write.

Signed-off-by: Luca Coelho <[email protected]>
Reviewed-by: Mika Kahola <[email protected]>
Signed-off-by: Mika Kahola <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: lucacoelho

drivers/gpu/drm/i915/display/intel_dkl_phy.c

@@ -25,7 +25,9 @@ dkl_phy_set_hip_idx(struct intel_display *display, struct intel_dkl_phy_reg reg)
 {
 	enum tc_port tc_port = DKL_REG_TC_PORT(reg);
 
-	drm_WARN_ON(display->drm, tc_port < TC_PORT_1 || tc_port >= I915_MAX_TC_PORTS);
+	if (drm_WARN_ON(display->drm,
+			tc_port < TC_PORT_1 || tc_port >= I915_MAX_TC_PORTS))
+		return;
 
 	intel_de_write(display,
 		       HIP_INDEX_REG(tc_port),