drm/i915: Make data/link N value power of two

From Ville Syrjala
16f091c6e04b5ac247d7b3b3764c2fbe8683e497 in ubuntu 3.8
a65851af59387146a28a928c3e7bb17dabc5db72 in mainline linux

2 files changed, 21 insertions, 18 deletions

diff --git a/sys/dev/pci/drm/i915/i915_reg.h b/sys/dev/pci/drm/i915/i915_reg.h
index 17b24d054db..0a13c26f0fa 100644
--- a/sys/dev/pci/drm/i915/i915_reg.h
+++ b/sys/dev/pci/drm/i915/i915_reg.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: i915_reg.h,v 1.6 2014/02/01 09:32:05 jsg Exp $	*/
+/*	$OpenBSD: i915_reg.h,v 1.7 2014/02/02 04:02:04 jsg Exp $	*/
 /* Copyright 2003 Tungsten Graphics, Inc., Cedar Park, Texas.
  * All Rights Reserved.
  *
@@ -2606,14 +2606,14 @@
 #define _PIPEB_GMCH_DATA_M			0x71050
 
 /* Transfer unit size for display port - 1, default is 0x3f (for TU size 64) */
-#define   PIPE_GMCH_DATA_M_TU_SIZE_MASK		(0x3f << 25)
-#define   PIPE_GMCH_DATA_M_TU_SIZE_SHIFT	25
+#define  TU_SIZE(x)             (((x)-1) << 25) /* default size 64 */
+#define  TU_SIZE_MASK           (0x3f << 25)
 
-#define   PIPE_GMCH_DATA_M_MASK			(0xffffff)
+#define  DATA_LINK_M_N_MASK	(0xffffff)
+#define  DATA_LINK_N_MAX	(0x800000)
 
 #define _PIPEA_GMCH_DATA_N			0x70054
 #define _PIPEB_GMCH_DATA_N			0x71054
-#define   PIPE_GMCH_DATA_N_MASK			(0xffffff)
 
 /*
  * Computing Link M and N values for the Display Port link
@@ -2628,11 +2628,9 @@
 
 #define _PIPEA_DP_LINK_M				0x70060
 #define _PIPEB_DP_LINK_M				0x71060
-#define   PIPEA_DP_LINK_M_MASK			(0xffffff)
 
 #define _PIPEA_DP_LINK_N				0x70064
 #define _PIPEB_DP_LINK_N				0x71064
-#define   PIPEA_DP_LINK_N_MASK			(0xffffff)
 
 #define PIPE_GMCH_DATA_M(pipe) _PIPE(pipe, _PIPEA_GMCH_DATA_M, _PIPEB_GMCH_DATA_M)
 #define PIPE_GMCH_DATA_N(pipe) _PIPE(pipe, _PIPEA_GMCH_DATA_N, _PIPEB_GMCH_DATA_N)
@@ -3298,8 +3296,6 @@
 
 
 #define _PIPEA_DATA_M1           0x60030
-#define  TU_SIZE(x)             (((x)-1) << 25) /* default size 64 */
-#define  TU_SIZE_MASK           0x7e000000
 #define  PIPE_DATA_M1_OFFSET    0
 #define _PIPEA_DATA_N1           0x60034
 #define  PIPE_DATA_N1_OFFSET    0
diff --git a/sys/dev/pci/drm/i915/intel_display.c b/sys/dev/pci/drm/i915/intel_display.c
index 019ce41cb5f..e9225ffccb1 100644
--- a/sys/dev/pci/drm/i915/intel_display.c
+++ b/sys/dev/pci/drm/i915/intel_display.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: intel_display.c,v 1.26 2014/01/24 06:11:02 jsg Exp $	*/
+/*	$OpenBSD: intel_display.c,v 1.27 2014/02/02 04:02:04 jsg Exp $	*/
 /*
  * Copyright © 2006-2007 Intel Corporation
  *
@@ -4144,26 +4144,33 @@ struct fdi_m_n {
 static void
 fdi_reduce_ratio(u32 *num, u32 *den)
 {
-	while (*num > 0xffffff || *den > 0xffffff) {
+	while (*num > DATA_LINK_M_N_MASK ||
+	       *den > DATA_LINK_M_N_MASK) {
 		*num >>= 1;
 		*den >>= 1;
 	}
 }
 
+static void compute_m_n(unsigned int m, unsigned int n,
+			uint32_t *ret_m, uint32_t *ret_n)
+{
+	*ret_n = min_t(unsigned int, roundup_pow_of_two(n), DATA_LINK_N_MAX);
+	*ret_m = div_u64((uint64_t) m * *ret_n, n);
+	fdi_reduce_ratio(ret_m, ret_n);
+}
+
 static void
 ironlake_compute_m_n(int bits_per_pixel, int nlanes, int pixel_clock,
 		     int link_clock, struct fdi_m_n *m_n)
 {
 	m_n->tu = 64; /* default size */
 
-	/* BUG_ON(pixel_clock > INT_MAX / 36); */
-	m_n->gmch_m = bits_per_pixel * pixel_clock;
-	m_n->gmch_n = link_clock * nlanes * 8;
-	fdi_reduce_ratio(&m_n->gmch_m, &m_n->gmch_n);
+	compute_m_n(bits_per_pixel * pixel_clock,
+		    link_clock * nlanes * 8,
+		    &m_n->gmch_m, &m_n->gmch_n);
 
-	m_n->link_m = pixel_clock;
-	m_n->link_n = link_clock;
-	fdi_reduce_ratio(&m_n->link_m, &m_n->link_n);
+	compute_m_n(pixel_clock, link_clock,
+		    &m_n->link_m, &m_n->link_n);
 }
 
 static inline bool intel_panel_use_ssc(struct drm_i915_private *dev_priv)