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drm/i915: increase default latency constant (v2 w/comment)

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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>
This commit is contained in:
Jesse Barnes 2009-08-31 10:24:31 -07:00 committed by Eric Anholt
parent 37d0892c5a
commit bcc24fb425
1 changed files with 15 additions and 1 deletions
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16
drivers/gpu/drm/i915/intel_display.c
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@ -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)
{