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drm/i915: Death to the unnecessary 64bit divide

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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
This commit is contained in:
Chris Wilson 2010-12-04 01:01:29 +00:00
parent 47f1c6c9ff
commit 22ed1113a9
1 changed files with 5 additions and 13 deletions
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18
drivers/gpu/drm/i915/intel_display.c
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@ -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);
}