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drm/i915: prevent FIFO calculation overflows on 32 bits with high dotclocks 

A very high dotclock (e.g. 229500kHz as reported by Anton) can cause
the entries_required variable to overflow, potentially leading to a
FIFO watermark value that's too low to support the given mode.  Split
the division across the calculation to avoid this.

Cc: stable@kernel.org
Reported-by: Anton Khirnov <wyskas@gmail.com>
Tested-by: Anton Khirnov <wyskas@gmail.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>
This commit is contained in:
Jesse Barnes 2009-09-11 12:25:56 -07:00
parent decbbcda29
commit d660467c3f
1 changed files with 8 additions and 1 deletions
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9
drivers/gpu/drm/i915/intel_display.c
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@ -2119,7 +2119,14 @@ static unsigned long intel_calculate_wm(unsigned long clock_in_khz,
{
long entries_required, wm_size;
entries_required = (clock_in_khz * pixel_size * latency_ns) / 1000000;
/*
* Note: we need to make sure we don't overflow for various clock &
* latency values.
* clocks go from a few thousand to several hundred thousand.
* latency is usually a few thousand
*/
entries_required = ((clock_in_khz / 1000) * pixel_size * latency_ns) /
1000;
entries_required /= wm->cacheline_size;
DRM_DEBUG("FIFO entries required for mode: %d\n", entries_required);