[Bug 108081] LG 31MU97 monitor native resolution is 4096x2160, but highest mode found is 3840x2160

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=108081

--- Comment #14 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to Brian Vincent from comment #13)
> Created attachment 141777 [details]
> 31mu97 EDID when attaching to amdgpu
> 
> When I attach this same monitor to my other computer with an AMDGPU, I get
> the attached EDID and the mode 4096x2160 is actually found.  So this is
> probably what the proper EDID is supposed to look like, right?

Interesting. The extra block is the DisplayID as I suspected. amdgpu uses the
same MST sideband code that i915 uses, so can't immediately see how it could
get different results.

Looking at the earlier i915 logs I see a bunch of
[    6.899169] [drm:drm_dp_mst_hpd_irq [drm_kms_helper]] Got NAK reply: req
0x22, reason 0x09, nak data 0x40

Those are REMOTE_I2C_READ/I2C_NAK replies with NAK_data 0x40 (which the spec
doesn't say what it means). Could be the remaining amount of data or something
I suppose.

Can you grab similar logs from amdgpu to see if we get any of those errors
there?

The only clear difference I see with amdgpu vs. i915 is the number of ESI
registers we read when processing the hpd irq. The following diff should make
i915 match amdgpu behaviour:
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 8e465095fe06..3f94dcc96f22 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -43,7 +43,7 @@
 #include <drm/i915_drm.h>
 #include "i915_drv.h"

-#define DP_DPRX_ESI_LEN 14
+#define DP_DPRX_ESI_LEN 4

 /* Compliance test status bits  */
 #define INTEL_DP_RESOLUTION_SHIFT_MASK 0

-- 
You are receiving this mail because:
You are the assignee for the bug.
You are on the CC list for the bug.
You are the QA Contact for the bug.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.freedesktop.org/archives/intel-gfx-bugs/attachments/20180928/71cac84b/attachment.html>