Re: [PATCH v3 2/9] drm/i915/skl+: use linetime latency instead of ddb size

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Hi,


On Monday 19 September 2016 11:54 PM, Zanoni, Paulo R wrote:
Em Seg, 2016-09-19 às 15:19 -0300, Paulo Zanoni escreveu:
Em Sex, 2016-09-09 às 13:30 +0530, Kumar, Mahesh escreveu:
From: Mahesh Kumar <mahesh1.kumar@xxxxxxxxx>

This patch make changes to use linetime latency instead of
allocated
DDB size during plane watermark calculation in switch case, This is
required to implement new DDB allocation algorithm.

In New Algorithm DDB is allocated based on WM values, because of
which
number of DDB blocks will not be available during WM calculation,
So this "linetime latency" is suggested by SV/HW team to use during
switch-case for WM blocks selection.
Why is this not part of BSpec? If there's some problem with the
current
algorithm and we need a new one, why is it not part of our spec?

This is now included in BSpec.... :)

Changes since v1:
  - Rebase on top of Paulo's patch series

Signed-off-by: Mahesh Kumar <mahesh1.kumar@xxxxxxxxx>
---
  drivers/gpu/drm/i915/intel_pm.c | 7 ++++++-
  1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c
b/drivers/gpu/drm/i915/intel_pm.c
index 3fdec4d..cfd9b7d1 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3622,10 +3622,15 @@ static int skl_compute_plane_wm(const
struct
drm_i915_private *dev_priv,
  	    fb->modifier[0] == I915_FORMAT_MOD_Yf_TILED) {
  		selected_result = max(method2, y_tile_minimum);
  	} else {
+		uint32_t linetime_us = 0;
+
+		linetime_us = DIV_ROUND_UP(width * 1000,
+				skl_pipe_pixel_rate(cstate));
Also, shouldn't this be width * 8 * 1000?
we don't need to multiply by 8 here, as this is the time taken for single line to be fetched.

thanks,
-Mahesh

+
  		if ((cpp * cstate->base.adjusted_mode.crtc_htotal
/
512 < 1) &&
  		    (plane_bytes_per_line / 512 < 1))
  			selected_result = method2;
-		else if ((ddb_allocation / plane_blocks_per_line)
=
1)
+		if (latency >= linetime_us)
  			selected_result = min(method1, method2);
  		else
  			selected_result = method1;
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