[Bug 110675] Regression: EDP panel flickers with linux 5.1+

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=110675

Ville Syrjala <ville.syrjala at linux.intel.com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |NEEDINFO

--- Comment #9 from Ville Syrjala <ville.syrjala at linux.intel.com> ---
(In reply to theli.ua from comment #6)
> Proposed hack doesn't change the outcome - it still flickers.
> 
> However, if I change it to the opposite  - ie to always take min_t path then
> that seem to fix the flickering.

That is strange.

The new 5.1 log still shows:
[   12.292716] [drm:intel_dump_pipe_config] dp m_n: lanes: 2; gmch_m: 5146655,
gmch_n: 8388608, link_m: 285925, link_n: 524288, tu: 64
[   12.292717] [drm:intel_dump_pipe_config] dp m2_n2: lanes: 2; gmch_m: 16044,
gmch_n: 32768, link_m: 14261, link_n: 32768, tu: 64

which does not make any sense to me. The N values should all be 0x8000 for both
dp_m_n and dp_m2_n2.


Can you try something like this so we can maybe see what's going on?

--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -6916,8 +6916,12 @@ static void compute_m_n(unsigned int m, unsigned int n,
        else
                *ret_n = min_t(unsigned int, roundup_pow_of_two(n),
DATA_LINK_N_MAX);

+       DRM_DEBUG_KMS("N = %d, constant_n = %d\n", *ret_n, constant_n);
+
        *ret_m = div_u64((u64)m * *ret_n, n);
        intel_reduce_m_n_ratio(ret_m, ret_n);
+
+       DRM_DEBUG_KMS("final N = %d, constant_n = %d\n", *ret_n, constant_n);
 }

 void

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