Thanks Stan for the review.
On 3/9/2023 4:14 PM, Lisovskiy, Stanislav wrote:
On Thu, Feb 23, 2023 at 05:25:09PM +0530, Ankit Nautiyal wrote:
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>
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@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
