drm/i915: Death to the unnecessary 64bit divide

Use the hardware DDA to calculate the ratio with as much accuracy as is
possible.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index e5badadbdcd26e9d030da779948086e7fddda7c9..fac118b2df7d6297f0520b048cc3d0496dbee7f8 100644 (file)
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2714,27 +2714,19 @@ fdi_reduce_ratio(u32 *num, u32 *den)
        }
 }
 
-#define DATA_N 0x800000
-#define LINK_N 0x80000
-
 static void
 ironlake_compute_m_n(int bits_per_pixel, int nlanes, int pixel_clock,
                     int link_clock, struct fdi_m_n *m_n)
 {
-       u64 temp;
-
        m_n->tu = 64; /* default size */
 
-       temp = (u64) DATA_N * pixel_clock;
-       temp = div_u64(temp, link_clock);
-       m_n->gmch_m = div_u64(temp * bits_per_pixel, nlanes);
-       m_n->gmch_m >>= 3; /* convert to bytes_per_pixel */
-       m_n->gmch_n = DATA_N;
+       /* 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);
 
-       temp = (u64) LINK_N * pixel_clock;
-       m_n->link_m = div_u64(temp, link_clock);
-       m_n->link_n = LINK_N;
+       m_n->link_m = pixel_clock;
+       m_n->link_n = link_clock;
        fdi_reduce_ratio(&m_n->link_m, &m_n->link_n);
 }