[PATCH 1/5] drm: Propagate error from connector dpms function in drm_fb_helper_blank()

[Takashi Iwai]

Currently the DRM fbcon helper for console blank,
drm_fb_helper_blank(), simply calls drm_fb_helper_dpms() and always
returns zero, supposing the driver dealing with DPMS properly for
blanking the screen.  However, it turned out that the console blank
doesn't work at all on KVM/QEMU when DRM driver is used: most of the
relevant drivers (bochs, qxl, and virtio) just ignore DPMS, and even
cirrus driver doesn't work because the DPMS register bits the driver
fiddles with are also ignored by KVM/QEMU.

A simple fix for this problem would be not to rely on DPMS but let
fbcon performs the generic blank code.  This can be achieved just by
returning an error from drm_fb_helper_blank().

In this patch, we change the drm_fb_helper_dpms() to give back an
error code returned from the connector dpms callback, so that the
error is propagated to drm_fb_helper_blank().  After this change, each
driver needs just to return an error to fall back to the generic fbcon
blank mode.

Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 drivers/gpu/drm/drm_fb_helper.c | 30 ++++++++++++++++++++----------
 1 file changed, 20 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index 574af01d3ce9..db31747ae598 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -581,21 +581,22 @@ static struct sysrq_key_op sysrq_drm_fb_helper_restore_op = {
 static struct sysrq_key_op sysrq_drm_fb_helper_restore_op = { };
 #endif
 
-static void drm_fb_helper_dpms(struct fb_info *info, int dpms_mode)
+static int drm_fb_helper_dpms(struct fb_info *info, int dpms_mode)
 {
 	struct drm_fb_helper *fb_helper = info->par;
 	struct drm_device *dev = fb_helper->dev;
 	struct drm_crtc *crtc;
 	struct drm_connector *connector;
 	int i, j;
+	int ret = 0;
 
 	/*
 	 * For each CRTC in this fb, turn the connectors on/off.
 	 */
 	drm_modeset_lock_all(dev);
 	if (!drm_fb_helper_is_bound(fb_helper)) {
-		drm_modeset_unlock_all(dev);
-		return;
+		ret = -ENODEV;
+		goto out;
 	}
 
 	for (i = 0; i < fb_helper->crtc_count; i++) {
@@ -607,12 +608,16 @@ static void drm_fb_helper_dpms(struct fb_info *info, int dpms_mode)
 		/* Walk the connectors & encoders on this fb turning them on/off */
 		drm_fb_helper_for_each_connector(fb_helper, j) {
 			connector = fb_helper->connector_info[j]->connector;
-			connector->funcs->dpms(connector, dpms_mode);
+			ret = connector->funcs->dpms(connector, dpms_mode);
+			if (ret < 0)
+				goto out;
 			drm_object_property_set_value(&connector->base,
 				dev->mode_config.dpms_property, dpms_mode);
 		}
 	}
+ out:
 	drm_modeset_unlock_all(dev);
+	return ret;
 }
 
 /**
@@ -622,32 +627,37 @@ static void drm_fb_helper_dpms(struct fb_info *info, int dpms_mode)
  */
 int drm_fb_helper_blank(int blank, struct fb_info *info)
 {
+	int dpms_mode;
+
 	if (oops_in_progress)
 		return -EBUSY;
 
 	switch (blank) {
 	/* Display: On; HSync: On, VSync: On */
 	case FB_BLANK_UNBLANK:
-		drm_fb_helper_dpms(info, DRM_MODE_DPMS_ON);
+		dpms_mode = DRM_MODE_DPMS_ON;
 		break;
 	/* Display: Off; HSync: On, VSync: On */
 	case FB_BLANK_NORMAL:
-		drm_fb_helper_dpms(info, DRM_MODE_DPMS_STANDBY);
+		dpms_mode = DRM_MODE_DPMS_STANDBY;
 		break;
 	/* Display: Off; HSync: Off, VSync: On */
 	case FB_BLANK_HSYNC_SUSPEND:
-		drm_fb_helper_dpms(info, DRM_MODE_DPMS_STANDBY);
+		dpms_mode = DRM_MODE_DPMS_STANDBY;
 		break;
 	/* Display: Off; HSync: On, VSync: Off */
 	case FB_BLANK_VSYNC_SUSPEND:
-		drm_fb_helper_dpms(info, DRM_MODE_DPMS_SUSPEND);
+		dpms_mode = DRM_MODE_DPMS_SUSPEND;
 		break;
 	/* Display: Off; HSync: Off, VSync: Off */
 	case FB_BLANK_POWERDOWN:
-		drm_fb_helper_dpms(info, DRM_MODE_DPMS_OFF);
+		dpms_mode = DRM_MODE_DPMS_OFF;
 		break;
+	default:
+		return 0; /* ignored */
 	}
-	return 0;
+
+	return drm_fb_helper_dpms(info, dpms_mode);
 }
 EXPORT_SYMBOL(drm_fb_helper_blank);
 
-- 
2.13.3