[PATCH 1/2] drm/i915/dkl: return if tc_port is invalid in dkl_phy_set_hip_idx()

[Luca Coelho]

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 <luciano.coelho at intel.com>
---
 drivers/gpu/drm/i915/display/intel_dkl_phy.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/display/intel_dkl_phy.c b/drivers/gpu/drm/i915/display/intel_dkl_phy.c
index dad7192132ad..35e919eae369 100644
--- a/drivers/gpu/drm/i915/display/intel_dkl_phy.c
+++ b/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),
-- 
2.47.2