[PATCH 3.16.y-ckt 16/58] drm/radeon: fix PLLs on RS880 and older v2

[Luis Henriques]

3.16.7-ckt7 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig at amd.com>

commit 72edd83cc9e5819ed1ee771519143d7594e059f0 upstream.

This is a workaround for RS880 and older chips which seem to have
an additional limit on the minimum PLL input frequency.

v2: fix signed/unsigned warning

bugs:
https://bugzilla.kernel.org/show_bug.cgi?id=91861
https://bugzilla.kernel.org/show_bug.cgi?id=83461

Signed-off-by: Christian König <christian.koenig at amd.com>
Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/gpu/drm/radeon/radeon_display.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
index bf25061c8ac4..13ac29b1fa0c 100644
--- a/drivers/gpu/drm/radeon/radeon_display.c
+++ b/drivers/gpu/drm/radeon/radeon_display.c
@@ -1000,6 +1000,9 @@ void radeon_compute_pll_avivo(struct radeon_pll *pll,
 	if (pll->flags & RADEON_PLL_USE_FRAC_FB_DIV &&
 	    pll->flags & RADEON_PLL_USE_REF_DIV)
 		ref_div_max = pll->reference_div;
+	else if (pll->flags & RADEON_PLL_PREFER_MINM_OVER_MAXP)
+		/* fix for problems on RS880 */
+		ref_div_max = min(pll->max_ref_div, 7u);
 	else
 		ref_div_max = pll->max_ref_div;
 
-- 
2.1.4