[Bug 112018] I7-8700 onboard HDMI port does not support 4K resolution

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=112018

--- Comment #2 from jian-hong at endlessm.com ---
Created attachment 145753
  --> https://bugs.freedesktop.org/attachment.cgi?id=145753&action=edit
dmesg with removed type 1 HDMI's max TMDS clock upper bound

If I remove the type 1 HDMI clock's upper bound like the diff based on latest
mainline kernel, than we can have 4K on this desktop:

diff --git a/drivers/gpu/drm/drm_dp_dual_mode_helper.c
b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
index 1c9ea9f7fdaf..da30f4cfb01e 100644
--- a/drivers/gpu/drm/drm_dp_dual_mode_helper.c
+++ b/drivers/gpu/drm/drm_dp_dual_mode_helper.c
@@ -277,12 +277,12 @@ int drm_dp_dual_mode_max_tmds_clock(enum
drm_dp_dual_mode_type type,
         * Type 1 adaptors are limited to 165MHz
         * Type 2 adaptors can tells us their limit
         */
-       if (type < DRM_DP_DUAL_MODE_TYPE2_DVI)
+       if (type < DRM_DP_DUAL_MODE_TYPE1_DVI)
                return 165000;

        ret = drm_dp_dual_mode_read(adapter, DP_DUAL_MODE_MAX_TMDS_CLOCK,
                                    &max_tmds_clock, sizeof(max_tmds_clock));
-       if (ret || max_tmds_clock == 0x00 || max_tmds_clock == 0xff) {
+       if (ret || max_tmds_clock == 0x00) {
                DRM_DEBUG_KMS("Failed to query max TMDS clock\n");
                return 165000;
        }

The type 1 HDMI's max TMDS clock becomes 637500 kHz, which is higher than the
expectation of 3840x2160.

[    3.951002] [drm:drm_dp_dual_mode_detect [drm_kms_helper]] DP dual mode HDMI
ID: DP-HDMI ADAPTOR\004 (err 0)
[    3.951966] [drm:drm_dp_dual_mode_detect [drm_kms_helper]] DP dual mode
adaptor ID: ff (err 0)
[    3.952970] [drm:intel_hdmi_set_edid [i915]] DP dual mode adaptor (type 1
HDMI) detected (max TMDS clock: 637500 kHz)

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