drm: Change limited M/N quirk to constant N quirk.

Some DP dongles in particular seem to be fussy about too large
link M/N values. Set specific value for N divider can resolve
this issue per dongle vendor's comment. So configure N as
constant value (0x8000) to instead of reduce M/N formula when
specific DP dongle connected.

v2: add more comments for issue description and fix typo.
v3: add lost commit messages back for version 2
v4: send patch to both intel-gfx and dri-devel

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Cooper Chiou <cooper.chiou@intel.com>
Cc: Matt Atwood <matthew.s.atwood@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Cc: Clint Taylor <clinton.a.taylor@intel.com>
Tested-by: Clint Taylor <clinton.a.taylor@intel.com>
Signed-off-by: Lee, Shawn C <shawn.c.lee@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1536733371-25004-3-git-send-email-shawn.c.lee@intel.com

1 files changed, 3 insertions, 3 deletions

diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 698082a02b97..2a3843f248cf 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -1261,12 +1261,12 @@ int drm_dp_read_desc(struct drm_dp_aux *aux, struct drm_dp_desc *desc,
  */
 enum drm_dp_quirk {
         /**
-         * @DP_DPCD_QUIRK_LIMITED_M_N:
+         * @DP_DPCD_QUIRK_CONSTANT_N:
          *
          * The device requires main link attributes Mvid and Nvid to be limited
-         * to 16 bits.
+         * to 16 bits. So will give a constant value (0x8000) for compatability.
          */
-        DP_DPCD_QUIRK_LIMITED_M_N,
+        DP_DPCD_QUIRK_CONSTANT_N,
 };
 
 /**