drm/i915: Fix not finding the VBT when it overlaps with OPREGION_ASLE_EXT

commit 998d75730b40afc218c059d811869abe9676b305 upstream.

If there is no OPREGION_ASLE_EXT then a VBT stored in mailbox #4 may
use the ASLE_EXT parts of the opregion. Adjust the vbt_size calculation
for a vbt in mailbox #4 for this.

This fixes the driver not finding the VBT on a jumper ezpad mini3
cherrytrail tablet and on a ACER SW5_017 machine.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1487088758-30050-1-git-send-email-jani.nikula@intel.com
(cherry picked from commit dfb65e71ea2c1d97ac373cc0587dc60b3307581a)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 12 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/intel_opregion.c b/drivers/gpu/drm/i915/intel_opregion.c
index 7acbbbf97833..4534e4cadccf 100644
--- a/drivers/gpu/drm/i915/intel_opregion.c
+++ b/drivers/gpu/drm/i915/intel_opregion.c
@@ -1031,7 +1031,18 @@ int intel_opregion_setup(struct drm_i915_private *dev_priv)
                         opregion->vbt_size = vbt_size;
                 } else {
                         vbt = base + OPREGION_VBT_OFFSET;
-                        vbt_size = OPREGION_ASLE_EXT_OFFSET - OPREGION_VBT_OFFSET;
+                        /*
+                         * The VBT specification says that if the ASLE ext
+                         * mailbox is not used its area is reserved, but
+                         * on some CHT boards the VBT extends into the
+                         * ASLE ext area. Allow this even though it is
+                         * against the spec, so we do not end up rejecting
+                         * the VBT on those boards (and end up not finding the
+                         * LCD panel because of this).
+                         */
+                        vbt_size = (mboxes & MBOX_ASLE_EXT) ?
+                                OPREGION_ASLE_EXT_OFFSET : OPREGION_SIZE;
+                        vbt_size -= OPREGION_VBT_OFFSET;
                         if (intel_bios_is_valid_vbt(vbt, vbt_size)) {
                                 DRM_DEBUG_KMS("Found valid VBT in ACPI OpRegion (Mailbox #4)\n");
                                 opregion->vbt = vbt;