drm/i915: Use intel_plane_data_rate for min_cdclk calculation

There seems to be a bit of confusing redundancy in a way, how
plane data rate/min cdclk are calculated.
In fact both min cdclk, pixel rate and plane data rate are all
part of the same formula as per BSpec.

However currently we have intel_plane_data_rate, which is used
to calculate plane data rate and which is also used in bandwidth
calculations. However for calculating min_cdclk we have another
piece of code, doing almost same calculation, but a bit differently
and in a different place. However as both are actually part of same
formula, probably would be wise to use plane data rate calculations
as a basis anyway, thus avoiding code duplication and possible bugs
related to this.

Another thing is that I've noticed that during min_cdclk calculations
we account for plane scaling, while for plane data rate, we don't.
crtc->pixel_rate seems to account only for pipe ratio, however it is
clearly stated in BSpec that plane data rate also need to account
plane ratio as well.

So what this commit does is:
- Adds a plane ratio calculation to intel_plane_data_rate
- Removes redundant calculations from skl_plane_min_cdclk which is
  used for gen9+ and now uses intel_plane_data_rate as a basis from
  there as well.

v2: - Don't use 64 division if not needed(Ville Syrjälä)
    - Now use intel_plane_pixel_rate as a basis for calculations both
      at intel_plane_data_rate and skl_plane_min_cdclk(Ville Syrjälä)

v3: - Again fix the division macro
    - Fix plane_pixel_rate to pixel_rate at intel_plane_pixel_rate
      callsites

v4: - Renamed skl_plane_ratio function back(Ville Syrjälä)

v5: - Don't precalculate plane pixel rate for invisible plane,
      check for visibility first, as in invisible case it will
      have dst_w and dst_h equal to zero, causing divide error.

v6: - Removed useless warn in intel_plane_pixel_rate(Ville Syrjälä)
    - Fixed alignment in intel_plane_data_rate(Ville Syrjälä)
    - Changed pixel_rate type to be unsigned int in
      skl_plane_min_cdclk(Ville Syrjälä)
Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200227150935.2107-1-stanislav.lisovskiy@intel.com

drivers/gpu/drm/i915/display/intel_atomic_plane.c

@@ -133,15 +133,37 @@ intel_plane_destroy_state(struct drm_plane *plane,
 	kfree(plane_state);
 }
 
+unsigned int intel_plane_pixel_rate(const struct intel_crtc_state *crtc_state,
+				    const struct intel_plane_state *plane_state)
+{
+	unsigned int src_w, src_h, dst_w, dst_h;
+	unsigned int pixel_rate = crtc_state->pixel_rate;
+
+	src_w = drm_rect_width(&plane_state->uapi.src) >> 16;
+	src_h = drm_rect_height(&plane_state->uapi.src) >> 16;
+	dst_w = drm_rect_width(&plane_state->uapi.dst);
+	dst_h = drm_rect_height(&plane_state->uapi.dst);
+
+	/* Downscaling limits the maximum pixel rate */
+	dst_w = min(src_w, dst_w);
+	dst_h = min(src_h, dst_h);
+
+	return DIV_ROUND_UP_ULL(mul_u32_u32(pixel_rate, src_w * src_h),
+				dst_w * dst_h);
+}
+
 unsigned int intel_plane_data_rate(const struct intel_crtc_state *crtc_state,
 				   const struct intel_plane_state *plane_state)
 {
 	const struct drm_framebuffer *fb = plane_state->hw.fb;
 	unsigned int cpp;
+	unsigned int pixel_rate;
 
 	if (!plane_state->uapi.visible)
 		return 0;
 
+	pixel_rate = intel_plane_pixel_rate(crtc_state, plane_state);
+
 	cpp = fb->format->cpp[0];
 
 	/*
@@ -153,7 +175,7 @@ unsigned int intel_plane_data_rate(const struct intel_crtc_state *crtc_state,
 	if (fb->format->is_yuv && fb->format->num_planes > 1)
 		cpp *= 4;
 
-	return cpp * crtc_state->pixel_rate;
+	return pixel_rate * cpp;
 }
 
 int intel_plane_calc_min_cdclk(struct intel_atomic_state *state,

drivers/gpu/drm/i915/display/intel_atomic_plane.h

@@ -18,6 +18,9 @@ struct intel_plane_state;
 
 extern const struct drm_plane_helper_funcs intel_plane_helper_funcs;
 
+unsigned int intel_plane_pixel_rate(const struct intel_crtc_state *crtc_state,
+				    const struct intel_plane_state *plane_state);
+
 unsigned int intel_plane_data_rate(const struct intel_crtc_state *crtc_state,
 				   const struct intel_plane_state *plane_state);
 void intel_plane_copy_uapi_to_hw_state(struct intel_plane_state *plane_state,

drivers/gpu/drm/i915/display/intel_sprite.c

@@ -364,9 +364,8 @@ static int skl_plane_min_cdclk(const struct intel_crtc_state *crtc_state,
 			       const struct intel_plane_state *plane_state)
 {
 	struct drm_i915_private *dev_priv = to_i915(plane_state->uapi.plane->dev);
-	unsigned int pixel_rate = crtc_state->pixel_rate;
-	unsigned int src_w, src_h, dst_w, dst_h;
 	unsigned int num, den;
+	unsigned int pixel_rate = intel_plane_pixel_rate(crtc_state, plane_state);
 
 	skl_plane_ratio(crtc_state, plane_state, &num, &den);
 
@@ -374,17 +373,7 @@ static int skl_plane_min_cdclk(const struct intel_crtc_state *crtc_state,
 	if (INTEL_GEN(dev_priv) >= 10 || IS_GEMINILAKE(dev_priv))
 		den *= 2;
 
-	src_w = drm_rect_width(&plane_state->uapi.src) >> 16;
-	src_h = drm_rect_height(&plane_state->uapi.src) >> 16;
-	dst_w = drm_rect_width(&plane_state->uapi.dst);
-	dst_h = drm_rect_height(&plane_state->uapi.dst);
-
-	/* Downscaling limits the maximum pixel rate */
-	dst_w = min(src_w, dst_w);
-	dst_h = min(src_h, dst_h);
-
-	return DIV64_U64_ROUND_UP(mul_u32_u32(pixel_rate * num, src_w * src_h),
-				  mul_u32_u32(den, dst_w * dst_h));
+	return DIV_ROUND_UP(pixel_rate * num, den);
 }
 
 static unsigned int