drm/i915: Use wait_for() to wait for Punit to change GPU freq on VLV

Use wait_for() instead of the open coded loop to avoid spreading the
same old timeout related bugs.

This changes the loop to use msleep(1) instead of udelay(10) when the
Punit had not yet completed the frequency change. In practice that
doesn't seem to hurt performance as the Punit appears to be ready pretty
much always.

Also give the status bit a name, instead of using the magic number 1.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_reg.h

@@ -363,6 +363,7 @@
 #define PUNIT_REG_GPU_LFM			0xd3
 #define PUNIT_REG_GPU_FREQ_REQ			0xd4
 #define PUNIT_REG_GPU_FREQ_STS			0xd8
+#define   GENFREQSTATUS				(1<<0)
 #define PUNIT_REG_MEDIA_TURBO_FREQ_REQ		0xdc
 
 #define PUNIT_FUSE_BUS2				0xf6 /* bits 47:40 */

drivers/gpu/drm/i915/intel_pm.c

@@ -3075,19 +3075,12 @@ void gen6_set_rps(struct drm_device *dev, u8 val)
  */
 static void vlv_update_rps_cur_delay(struct drm_i915_private *dev_priv)
 {
-	unsigned long timeout = jiffies + msecs_to_jiffies(10);
 	u32 pval;
 
 	WARN_ON(!mutex_is_locked(&dev_priv->rps.hw_lock));
 
-	do {
-		pval = vlv_punit_read(dev_priv, PUNIT_REG_GPU_FREQ_STS);
-		if (time_after(jiffies, timeout)) {
-			DRM_DEBUG_DRIVER("timed out waiting for Punit\n");
-			break;
-		}
-		udelay(10);
-	} while (pval & 1);
+	if (wait_for(((pval = vlv_punit_read(dev_priv, PUNIT_REG_GPU_FREQ_STS)) & GENFREQSTATUS) == 0, 10))
+		DRM_DEBUG_DRIVER("timed out waiting for Punit\n");
 
 	pval >>= 8;