Bug #11951: Fix an errno sign inversion on pre-FreeBSD 5.

Also, annotate where signs change, to hopefully remind the reader of these
issues in the future.

bsd-core/drmP.h

@@ -377,6 +377,7 @@ do {									\
 } while (0)
 
 #if defined(__FreeBSD__) && __FreeBSD_version > 500000
+/* Returns -errno to shared code */
 #define DRM_WAIT_ON( ret, queue, timeout, condition )		\
 for ( ret = 0 ; !ret && !(condition) ; ) {			\
 	DRM_UNLOCK();						\
@@ -388,11 +389,12 @@ for ( ret = 0 ; !ret && !(condition) ; ) {			\
 	DRM_LOCK();						\
 }
 #else
+/* Returns -errno to shared code */
 #define DRM_WAIT_ON( ret, queue, timeout, condition )	\
 for ( ret = 0 ; !ret && !(condition) ; ) {		\
         int s = spldrm();				\
 	if (!(condition))				\
-	   ret = tsleep( &(queue), PZERO | PCATCH, 	\
+	   ret = -tsleep( &(queue), PZERO | PCATCH, 	\
 			 "drmwtq", (timeout) );		\
 	splx(s);					\
 }

bsd-core/drm_dma.c

@@ -121,6 +121,7 @@ int drm_dma(drm_device_t *dev, void *data, struct drm_file *file_priv)
 {
 
 	if (dev->driver.dma_ioctl) {
+		/* shared code returns -errno */
 		return -dev->driver.dma_ioctl(dev, data, file_priv);
 	} else {
 		DRM_DEBUG("DMA ioctl on driver with no dma handler\n");

bsd-core/drm_fops.c

@@ -93,6 +93,7 @@ int drm_open_helper(struct cdev *kdev, int flags, int fmt, DRM_STRUCTPROC *p,
 		priv->authenticated	= DRM_SUSER(p);
 
 		if (dev->driver.open) {
+			/* shared code returns -errno */
 			retcode = -dev->driver.open(dev, priv);
 			if (retcode != 0) {
 				free(priv, M_DRM);

bsd-core/drm_irq.c

@@ -241,6 +241,7 @@ int drm_wait_vblank(drm_device_t *dev, void *data, struct drm_file *file_priv)
 		ret = EINVAL;
 	} else {
 		DRM_LOCK();
+		/* shared code returns -errno */
 		ret = -dev->driver.vblank_wait(dev,
 		    &vblwait->request.sequence);
 		DRM_UNLOCK();