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Commit 22ed1113 authored by Chris Wilson's avatar Chris Wilson
Browse files

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: default avatarChris Wilson <chris@chris-wilson.co.uk>
Cc: stable@kernel.org
parent 47f1c6c9
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+5 −13
Original line number Diff line number Diff line
@@ -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);
}