From d660467c3ff2a0b7413e1b7a51452b34ffb49e5f Mon Sep 17 00:00:00 2001 From: Jesse Barnes Date: Fri, 11 Sep 2009 12:25:56 -0700 Subject: [PATCH] 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 Tested-by: Anton Khirnov Signed-off-by: Jesse Barnes --- drivers/gpu/drm/i915/intel_display.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c index b6743281a97b..44234150e842 100644 --- a/drivers/gpu/drm/i915/intel_display.c +++ b/drivers/gpu/drm/i915/intel_display.c @@ -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);