Re: [Intel-gfx] [PATCH 6/9] drm/i915/gen9: fix plane_blocks_per_line on watermarks calculations

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On 22/09/2016 22:00, Paulo Zanoni wrote:
The confusing thing is that plane_blocks_per_line is listed as part of
the method 2 calculation but is also used for other things. We
calculated it in two different places and different ways: one inside
skl_wm_method2() and the other inside skl_compute_plane_wm(). The
skl_wm_method2() implementation is the one that matches the
specification.

With this patch we fix the skl_compute_plane_wm() calculation and just
pass it as a parameter to skl_wm_method2(). We also take care to not
modify the value of plane_bytes_per_line since we're going to rely on
it having a correct value in later patches.

This should affect the watermarks for Linear and Y-tiled.

 From my analysis, it looks like the two plane_blocks_per_line
variables got out of sync on 0fda65680e92, but we can't really say
that commit was a regression, it looks like just an incomplete fix.
There's always the possibility that 0fda65680e92 matched our
specification at that time, and then later the specification changed.

Yes, it wouldn't be a regression since before that commit changing tiling with page flips did not work at all.

Whether or not calculation was fully correct at the time I am not sure. The formulas changed at least twice after the initial implementation so both are possible.

Regards,

Tvrtko

v2: Try to add a "Fixes" tag (Maarten).

Fixes: 0fda65680e92 ("drm/i915/skl: Update watermarks for Y tiling")
Cc: stable@xxxxxxxxxxxxxxx
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Reviewed-by: Lyude <cpaul@xxxxxxxxxx>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@xxxxxxxxx>
---
  drivers/gpu/drm/i915/intel_pm.c | 39 +++++++++++++++------------------------
  1 file changed, 15 insertions(+), 24 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index a7f5f7f..a6ae7b7 100644
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3494,30 +3494,14 @@ static uint32_t skl_wm_method1(uint32_t pixel_rate, uint8_t cpp, uint32_t latenc
  }
static uint32_t skl_wm_method2(uint32_t pixel_rate, uint32_t pipe_htotal,
-			       uint32_t horiz_pixels, uint8_t cpp,
-			       uint64_t tiling, uint32_t latency,
-			       uint32_t y_min_scanlines)
+			       uint32_t latency, uint32_t plane_blocks_per_line)
  {
  	uint32_t ret;
-	uint32_t plane_bytes_per_line, plane_blocks_per_line;
  	uint32_t wm_intermediate_val;
if (latency == 0)
  		return UINT_MAX;
- plane_bytes_per_line = horiz_pixels * cpp;
-
-	if (tiling == I915_FORMAT_MOD_Y_TILED ||
-	    tiling == I915_FORMAT_MOD_Yf_TILED) {
-		plane_bytes_per_line *= y_min_scanlines;
-		plane_blocks_per_line = DIV_ROUND_UP(plane_bytes_per_line, 512);
-		plane_blocks_per_line /= y_min_scanlines;
-	} else if (tiling == DRM_FORMAT_MOD_NONE) {
-		plane_blocks_per_line = DIV_ROUND_UP(plane_bytes_per_line, 512) + 1;
-	} else {
-		plane_blocks_per_line = DIV_ROUND_UP(plane_bytes_per_line, 512);
-	}
-
  	wm_intermediate_val = latency * pixel_rate;
  	ret = DIV_ROUND_UP(wm_intermediate_val, pipe_htotal * 1000) *
  				plane_blocks_per_line;
@@ -3606,17 +3590,24 @@ static int skl_compute_plane_wm(const struct drm_i915_private *dev_priv,
  		y_min_scanlines = 4;
  	}
+ plane_bytes_per_line = width * cpp;
+	if (fb->modifier[0] == I915_FORMAT_MOD_Y_TILED ||
+	    fb->modifier[0] == I915_FORMAT_MOD_Yf_TILED) {
+		plane_blocks_per_line =
+		      DIV_ROUND_UP(plane_bytes_per_line * y_min_scanlines, 512);
+		plane_blocks_per_line /= y_min_scanlines;
+	} else if (fb->modifier[0] == DRM_FORMAT_MOD_NONE) {
+		plane_blocks_per_line = DIV_ROUND_UP(plane_bytes_per_line, 512)
+					+ 1;
+	} else {
+		plane_blocks_per_line = DIV_ROUND_UP(plane_bytes_per_line, 512);
+	}
+
  	method1 = skl_wm_method1(plane_pixel_rate, cpp, latency);
  	method2 = skl_wm_method2(plane_pixel_rate,
  				 cstate->base.adjusted_mode.crtc_htotal,
-				 width,
-				 cpp,
-				 fb->modifier[0],
  				 latency,
-				 y_min_scanlines);
-
-	plane_bytes_per_line = width * cpp;
-	plane_blocks_per_line = DIV_ROUND_UP(plane_bytes_per_line, 512);
+				 plane_blocks_per_line);
if (fb->modifier[0] == I915_FORMAT_MOD_Y_TILED ||
  	    fb->modifier[0] == I915_FORMAT_MOD_Yf_TILED) {

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