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authorJesse Barnes <jbarnes@virtuousgeek.org>2009-08-31 10:24:31 -0700
committerEric Anholt <eric@anholt.net>2009-09-02 10:33:01 -0700
commitbcc24fb42585dc9f490cf7789a917358414bdab5 (patch)
treeb9d48fecfd6ed4f5a0ba3b6c4837670612974d92
parent37d0892c5a94e208cf863e3b7bac014edee4346d (diff)
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drm/i915: increase default latency constant (v2 w/comment)
Some i915/i945 platforms have a fairly high memory latency in certain situations, so increase our constant a bit to avoid FIFO underruns. The effect should be positive on other platforms as well; we'll have a bit more insurance against a busy memory subsystem due to the extra FIFO entries. Fixes fdo bug #23368. Needed for 2.6.31. Tested-by: Sven Arvidsson <sa@whiz.se> Tested-by: Chris Wilson <chris@chris-wilson.co.uk> Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org> Signed-off-by: Eric Anholt <eric@anholt.net>
-rw-r--r--drivers/gpu/drm/i915/intel_display.c16
1 files changed, 15 insertions, 1 deletions
diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 3fadb535885..748ed50c55c 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -2005,7 +2005,21 @@ static void igd_enable_cxsr(struct drm_device *dev, unsigned long clock,
return;
}
-const static int latency_ns = 3000; /* default for non-igd platforms */
+/*
+ * Latency for FIFO fetches is dependent on several factors:
+ * - memory configuration (speed, channels)
+ * - chipset
+ * - current MCH state
+ * It can be fairly high in some situations, so here we assume a fairly
+ * pessimal value. It's a tradeoff between extra memory fetches (if we
+ * set this value too high, the FIFO will fetch frequently to stay full)
+ * and power consumption (set it too low to save power and we might see
+ * FIFO underruns and display "flicker").
+ *
+ * A value of 5us seems to be a good balance; safe for very low end
+ * platforms but not overly aggressive on lower latency configs.
+ */
+const static int latency_ns = 5000;
static int intel_get_fifo_size(struct drm_device *dev, int plane)
{