[PATCH 4.15 108/168] drm/i915/cnp: Properly handle VBT ddc pin out of bounds.

[Greg Kroah-Hartman]

4.15-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>

commit 6e3322c226f15bc1838007f5a75566f1482b8e40 upstream.

If the table result is out of bounds on the array map
there is something really wrong with VBT pin so we don't
return that vbt_pin, but only return 0 instead.

This basically reverts commit 'a8e6f3888b05 ("drm/i915/cnp:
Ignore VBT request for know invalid DDC pin.")'

Also this properly fixes commit 9c3b2689d01f ("drm/i915/cnl:
Map VBT DDC Pin to BSpec DDC Pin.")

v2: Do in a way that we don't break other platforms. (Jani)

v3: Keep debug message (Jani)

v4: Don't mess with 0 mapping was noticed by Jani and
    addressed with a simple solution suggested by Lucas
    that makes this even simpler.

Fixes: a8e6f3888b05 ("drm/i915/cnp: Ignore VBT request for know invalid DDC pin.")
Fixes: 9c3b2689d01f ("drm/i915/cnl: Map VBT DDC Pin to BSpec DDC Pin.")
Cc: Radhakrishna Sripada <radhakrishna.sripada@xxxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
Cc: Kai Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
Cc: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
Suggested-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Reviewed-by: Lucas De Marchi <lucas.demarchi@xxxxxxxxx>
Tested-by: Kai-Heng Feng <kai.heng.feng@xxxxxxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20180125222524.22059-1-rodrigo.vivi@xxxxxxxxx
(cherry picked from commit 3393ce1ed8fc43dbdb83952facaf04e644ca1d54)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 drivers/gpu/drm/i915/intel_bios.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/i915/intel_bios.c
+++ b/drivers/gpu/drm/i915/intel_bios.c
@@ -1107,6 +1107,7 @@ static void sanitize_aux_ch(struct drm_i
 }
 
 static const u8 cnp_ddc_pin_map[] = {
+	[0] = 0, /* N/A */
 	[DDC_BUS_DDI_B] = GMBUS_PIN_1_BXT,
 	[DDC_BUS_DDI_C] = GMBUS_PIN_2_BXT,
 	[DDC_BUS_DDI_D] = GMBUS_PIN_4_CNP, /* sic */
@@ -1116,9 +1117,9 @@ static const u8 cnp_ddc_pin_map[] = {
 static u8 map_ddc_pin(struct drm_i915_private *dev_priv, u8 vbt_pin)
 {
 	if (HAS_PCH_CNP(dev_priv)) {
-		if (vbt_pin > 0 && vbt_pin < ARRAY_SIZE(cnp_ddc_pin_map))
+		if (vbt_pin < ARRAY_SIZE(cnp_ddc_pin_map)) {
 			return cnp_ddc_pin_map[vbt_pin];
-		if (vbt_pin > GMBUS_PIN_4_CNP) {
+		} else {
 			DRM_DEBUG_KMS("Ignoring alternate pin: VBT claims DDC pin %d, which is not valid for this platform\n", vbt_pin);
 			return 0;
 		}