Comment 18 for bug 1791312

Indeed, the two radeon parameters for PLL mention in previous message
does not seems to appear anymore in modinfo radeon.

paul@paul-NC210-NC110:~/linux-stable$ git log --oneline v3.15-rc1..v3.15-rc2 | grep radeon
bcddee29b0b8 drm/radeon/ci: make sure mc ucode is loaded before checking the size
8c79bae6a30f drm/radeon/si: make sure mc ucode is loaded before checking the size
f8a2645ecede drm/radeon: improve PLL params if we don't match exactly v2
74073c9dd299 drm/radeon: memory leak on bo reservation failure. v2
681941c1790b drm/radeon: fix VCE fence command
7e1858f9aff7 drm/radeon: re-enable mclk dpm on R7 260X asics
277babc374f6 drm/radeon: add support for newer mc ucode on CI (v2)
1ebe92802eaf drm/radeon: add support for newer mc ucode on SI (v2)
5fb9cc4d8b16 drm/radeon: apply more strict limits for PLL params v2
6abc6d5c73b2 drm/radeon: update CI DPM powertune settings
90c4cde9d5a2 drm/radeon: fix runpm handling on APUs (v4)
57700ad1f2f2 drm/radeon: disable mclk dpm on R7 260X
8902e6f2b832 drm/radeon: Improve vramlimit module param documentation
be0949f5eb9c drm/radeon: fix audio pin counts for DCE6+ (v2)
379dfc25e257 drm/radeon/dp: switch to the common i2c over aux code
25377b921b40 drm/radeon/dp: handle zero sized i2c over aux transactions (v2)
paul@paul-NC210-NC110:~/linux-stable$

paul@paul-NC210-NC110:~/linux-stable$ git show 5fb9cc4d8b16
commit 5fb9cc4d8b1639b9a7487c1ee7b2b0c52877327d
Author: Christian König <email address hidden>
Date: Fri Apr 4 13:45:42 2014 +0200

    drm/radeon: apply more strict limits for PLL params v2

    Letting post and refernce divider get to big is bad for signal stability.

    v2: increase the limit to 210

    Signed-off-by: Christian König <email address hidden>

diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
index 386cfa4c194d..2f42912031ac 100644
--- a/drivers/gpu/drm/radeon/radeon_display.c
+++ b/drivers/gpu/drm/radeon/radeon_display.c
@@ -937,6 +937,9 @@ void radeon_compute_pll_avivo(struct radeon_pll *pll,
        }
        post_div = post_div_best;

+ /* limit reference * post divider to a maximum */
+ ref_div_max = min(210 / post_div, ref_div_max);
+
        /* get matching reference and feedback divider */
        ref_div = max(den / post_div, 1u);
        fb_div = nom;
paul@paul-NC210-NC110:~/linux-stable$
I might try to recompile kernel with that line commented out.
But it has been many years I did not compile a kernel.