drm/i915: Deal with machines that expose less than three QGV points

When SAGV is forced to disabled/min/med/max in the BIOS pcode will
only hand us a single QGV point instead of the normal three. Fix
the code to deal with that instead declaring the bandwidth limit
to be 0 MB/s (and thus preventing any planes from being enabled).

Also shrink the max_bw sturct a bit while at it, and change the
deratedbw type to unsigned since the code returns the bw as
an unsigned int.

Since we now keep track of how many qgv points we got from pcode
we can drop the earlier check added for the "pcode doesn't
support the memory subsystem query" case.

Cc: felix.j.degrood@intel.com
Cc: Mark Janes <mark.a.janes@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Clint Taylor <Clinton.A.Taylor@intel.com>
Fixes: c457d9c ("drm/i915: Make sure we have enough memory bandwidth on ICL")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110838
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190606124210.3482-1-ville.syrjala@linux.intel.com
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>

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

@@ -178,6 +178,8 @@ static int icl_get_bw_info(struct drm_i915_private *dev_priv)
 		clpchgroup = (sa->deburst * deinterleave / num_channels) << i;
 		bi->num_planes = (ipqdepth - clpchgroup) / clpchgroup + 1;
 
+		bi->num_qgv_points = qi.num_points;
+
 		for (j = 0; j < qi.num_points; j++) {
 			const struct intel_qgv_point *sp = &qi.points[j];
 			int ct, bw;
@@ -195,7 +197,7 @@ static int icl_get_bw_info(struct drm_i915_private *dev_priv)
 			bi->deratedbw[j] = min(maxdebw,
 					       bw * 9 / 10); /* 90% */
 
-			DRM_DEBUG_KMS("BW%d / QGV %d: num_planes=%d deratedbw=%d\n",
+			DRM_DEBUG_KMS("BW%d / QGV %d: num_planes=%d deratedbw=%u\n",
 				      i, j, bi->num_planes, bi->deratedbw[j]);
 		}
 
@@ -211,14 +213,17 @@ static unsigned int icl_max_bw(struct drm_i915_private *dev_priv,
 {
 	int i;
 
-	/* Did we initialize the bw limits successfully? */
-	if (dev_priv->max_bw[0].num_planes == 0)
-		return UINT_MAX;
-
 	for (i = 0; i < ARRAY_SIZE(dev_priv->max_bw); i++) {
 		const struct intel_bw_info *bi =
 			&dev_priv->max_bw[i];
 
+		/*
+		 * Pcode will not expose all QGV points when
+		 * SAGV is forced to off/min/med/max.
+		 */
+		if (qgv_point >= bi->num_qgv_points)
+			return UINT_MAX;
+
 		if (num_planes >= bi->num_planes)
 			return bi->deratedbw[qgv_point];
 	}

drivers/gpu/drm/i915/i915_drv.h

@@ -1673,8 +1673,9 @@ struct drm_i915_private {
 	} dram_info;
 
 	struct intel_bw_info {
-		int num_planes;
-		int deratedbw[3];
+		unsigned int deratedbw[3]; /* for each QGV point */
+		u8 num_qgv_points;
+		u8 num_planes;
 	} max_bw[6];
 
 	struct drm_private_obj bw_obj;