While computing compressed bpp, maximum value of bits_per_pixel is calculated that can be supported with the given link configuration for a given mode. Avoid rounding up of this max bits_per_pixel. Also improve documentation for computing max bits_per_pixel. Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@xxxxxxxxx> --- drivers/gpu/drm/i915/display/intel_dp.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c index b77bd4565864..51e9d0b2d8b3 100644 --- a/drivers/gpu/drm/i915/display/intel_dp.c +++ b/drivers/gpu/drm/i915/display/intel_dp.c @@ -716,9 +716,19 @@ u16 intel_dp_dsc_get_output_bpp(struct drm_i915_private *i915, * (LinkSymbolClock)* 8 * (TimeSlots / 64) * for SST -> TimeSlots is 64(i.e all TimeSlots that are available) * for MST -> TimeSlots has to be calculated, based on mode requirements + * + * Due to FEC overhead, the available bw is reduced to 97.2261%. + * To support the given mode: + * Bandwidth required should be <= Available link Bandwidth * FEC Overhead + * =>ModeClock * bits_per_pixel <= Available Link Bandwidth * FEC Overhead + * =>bits_per_pixel <= Available link Bandwidth * FEC Overhead / ModeClock + * =>bits_per_pixel <= (NumberOfLanes * LinkSymbolClock) * 8 (TimeSlots / 64) / + * (ModeClock / FEC Overhead) + * =>bits_per_pixel <= (NumberOfLanes * LinkSymbolClock * TimeSlots) / + * (ModeClock / FEC Overhead * 8) */ - bits_per_pixel = DIV_ROUND_UP((link_clock * lane_count) * timeslots, - intel_dp_mode_to_fec_clock(mode_clock) * 8); + bits_per_pixel = ((link_clock * lane_count) * timeslots) / + (intel_dp_mode_to_fec_clock(mode_clock) * 8); drm_dbg_kms(&i915->drm, "Max link bpp is %u for %u timeslots " "total bw %u pixel clock %u\n", -- 2.25.1
