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Groups > linux.kernel > #1484307

[PATCH 4/4] drm/sun4i: dotclock: Round to closest clock rate

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With display pixel clocks we want to have the closest possible clock
rate, to minimize timing and refresh rate skews. Whether the actual
clock rate is higher or lower than the requested rate is less important.

Also check candidates against the requested rate, rather than the
ideal parent rate, the varying dividers also influence the difference
between the requested rate and the rounded rate.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
---
 drivers/gpu/drm/sun4i/sun4i_dotclock.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/sun4i/sun4i_dotclock.c b/drivers/gpu/drm/sun4i/sun4i_dotclock.c
index 3eb99784f371..d401156490f3 100644
--- a/drivers/gpu/drm/sun4i/sun4i_dotclock.c
+++ b/drivers/gpu/drm/sun4i/sun4i_dotclock.c
@@ -90,7 +90,8 @@ static long sun4i_dclk_round_rate(struct clk_hw *hw, unsigned long rate,
 			goto out;
 		}
 
-		if ((rounded < ideal) && (rounded > best_parent)) {
+		if (abs(rate - rounded / i) <
+		    abs(rate - best_parent / best_div)) {
 			best_parent = rounded;
 			best_div = i;
 		}
-- 
2.9.3

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Thread

[PATCH 0/4] drm/sun4i: rgb and dotclock misc fixes and improvements Chen-Yu Tsai <wens@csie.org> - 2016-09-15 17:20 +0200
  [PATCH 1/4] drm/sun4i: rgb: Declare RGB encoder and connector as MIPI DPI Chen-Yu Tsai <wens@csie.org> - 2016-09-15 17:20 +0200
    Re: [PATCH 1/4] drm/sun4i: rgb: Declare RGB encoder and connector as  MIPI DPI Maxime Ripard <maxime.ripard@free-electrons.com> - 2016-09-18 21:20 +0200
      Re: [PATCH 1/4] drm/sun4i: rgb: Declare RGB encoder and connector as  MIPI DPI Chen-Yu Tsai <wens@csie.org> - 2016-09-19 17:30 +0200
  [PATCH 2/4] drm/sun4i: dotclock: Fix clock rate read back calcation Chen-Yu Tsai <wens@csie.org> - 2016-09-15 17:20 +0200
    Re: [PATCH 2/4] drm/sun4i: dotclock: Fix clock rate read back  calcation Maxime Ripard <maxime.ripard@free-electrons.com> - 2016-09-18 21:20 +0200
  [PATCH 4/4] drm/sun4i: dotclock: Round to closest clock rate Chen-Yu Tsai <wens@csie.org> - 2016-09-15 17:20 +0200
    Re: [PATCH 4/4] drm/sun4i: dotclock: Round to closest clock rate Maxime Ripard <maxime.ripard@free-electrons.com> - 2016-09-18 21:20 +0200
      Re: [PATCH 4/4] drm/sun4i: dotclock: Round to closest clock rate Chen-Yu Tsai <wens@csie.org> - 2016-09-19 17:40 +0200
        Re: [PATCH 4/4] drm/sun4i: dotclock: Round to closest clock rate Maxime Ripard <maxime.ripard@free-electrons.com> - 2016-09-20 17:50 +0200
    Re: [PATCH 4/4] drm/sun4i: dotclock: Round to closest clock rate Maxime Ripard <maxime.ripard@free-electrons.com> - 2016-09-20 17:50 +0200
  [PATCH 3/4] drm/sun4i: dotclock: Allow divider = 127 Chen-Yu Tsai <wens@csie.org> - 2016-09-15 17:20 +0200
    Re: [PATCH 3/4] drm/sun4i: dotclock: Allow divider = 127 Maxime Ripard <maxime.ripard@free-electrons.com> - 2016-09-18 21:20 +0200

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