drm/i915/skl: Make res_blocks/lines intermediate values 32 bits

To align with the ilk WM code and because it makes sense to test against
the upper bounds as soon as possible on variables that are bigger than
the number of bits in the register, let's move the maximum checks from
skl_compute_wm_results() to skl_compute_plane_wm().

v2: Leave the result values to 0 when overflowing the limits (Ville)
    Use 32 bits intermediate variables (Damien)

Instead of using the 16 and 8 bits space we have in the result
structure, use 32 bits local variables until we're sure they fit into
the constraints.

Suggested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_pm.c

@@ -3317,10 +3317,10 @@ static bool skl_compute_plane_wm(struct skl_pipe_wm_parameters *p,
 				   struct intel_plane_wm_parameters *p_params,
 				   uint16_t ddb_allocation,
 				   uint32_t mem_value,
-				   uint16_t *res_blocks, /* out */
-				   uint8_t *res_lines /* out */)
+				   uint16_t *out_blocks, /* out */
+				   uint8_t *out_lines /* out */)
 {
-	uint32_t method1, method2, plane_bytes_per_line;
+	uint32_t method1, method2, plane_bytes_per_line, res_blocks, res_lines;
 	uint32_t result_bytes;
 
 	if (mem_value == 0 || !p->active || !p_params->enabled)
@@ -3344,8 +3344,14 @@ static bool skl_compute_plane_wm(struct skl_pipe_wm_parameters *p,
 	else
 		result_bytes = method1;
 
-	*res_blocks = DIV_ROUND_UP(result_bytes, 512) + 1;
-	*res_lines = DIV_ROUND_UP(result_bytes, plane_bytes_per_line);
+	res_blocks = DIV_ROUND_UP(result_bytes, 512) + 1;
+	res_lines = DIV_ROUND_UP(result_bytes, plane_bytes_per_line);
+
+	if (res_blocks > ddb_allocation || res_lines > 31)
+		return false;
+
+	*out_blocks = res_blocks;
+	*out_lines = res_lines;
 
 	return true;
 }
@@ -3408,17 +3414,11 @@ static void skl_compute_wm_results(struct drm_device *dev,
 	enum pipe pipe = intel_crtc->pipe;
 
 	for (level = 0; level <= max_level; level++) {
-		uint16_t ddb_blocks;
 		uint32_t temp;
 		int i;
 
 		for (i = 0; i < intel_num_planes(intel_crtc); i++) {
 			temp = 0;
-			ddb_blocks = skl_ddb_entry_size(&r->ddb.plane[pipe][i]);
-
-			if ((p_wm->wm[level].plane_res_b[i] > ddb_blocks) ||
-				(p_wm->wm[level].plane_res_l[i] > 31))
-				p_wm->wm[level].plane_en[i] = false;
 
 			temp |= p_wm->wm[level].plane_res_l[i] <<
 					PLANE_WM_LINES_SHIFT;
@@ -3433,11 +3433,6 @@ static void skl_compute_wm_results(struct drm_device *dev,
 		}
 
 		temp = 0;
-		ddb_blocks = skl_ddb_entry_size(&r->ddb.cursor[pipe]);
-
-		if ((p_wm->wm[level].cursor_res_b > ddb_blocks) ||
-			(p_wm->wm[level].cursor_res_l > 31))
-			p_wm->wm[level].cursor_en = false;
 
 		temp |= p_wm->wm[level].cursor_res_l << PLANE_WM_LINES_SHIFT;
 		temp |= p_wm->wm[level].cursor_res_b;