[PATCH 3/3] drm/client: log: Implement struct drm_client_funcs.restore

[Thomas Zimmermann <tzimmermann@suse.de>]

Restore the log client's output when the DRM core invokes the restore
callback. Follow the existing behavior of fbdev emulation wrt. the
value of the force parameter.

If force is false, acquire the DRM master lock and reprogram the
display. This is the case when the user-space compositor exists and
the DRM core transfers the display back to the in-kernel client. This
also enables log output during reboots.

If force is true, reprogram without considering the master lock. This
overrides the current compositor and prints the log to the screen. In
case of system malfunction, users can enter SysRq+v to invoke the
emergency error reporting. See Documentation/admin-guide/sysrq.rst for
more information.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/clients/drm_log.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/gpu/drm/clients/drm_log.c b/drivers/gpu/drm/clients/drm_log.c
index 19e55aa0ed74..4d3005273b27 100644
--- a/drivers/gpu/drm/clients/drm_log.c
+++ b/drivers/gpu/drm/clients/drm_log.c
@@ -315,6 +315,18 @@ static void drm_log_client_unregister(struct drm_client_dev *client)
 	drm_client_release(client);
 }
 
+static int drm_log_client_restore(struct drm_client_dev *client, bool force)
+{
+	int ret;
+
+	if (force)
+		ret = drm_client_modeset_commit_locked(client);
+	else
+		ret = drm_client_modeset_commit(client);
+
+	return ret;
+}
+
 static int drm_log_client_hotplug(struct drm_client_dev *client)
 {
 	struct drm_log *dlog = client_to_drm_log(client);
@@ -348,6 +360,7 @@ static const struct drm_client_funcs drm_log_client_funcs = {
 	.owner		= THIS_MODULE,
 	.free		= drm_log_client_free,
 	.unregister	= drm_log_client_unregister,
+	.restore	= drm_log_client_restore,
 	.hotplug	= drm_log_client_hotplug,
 	.suspend	= drm_log_client_suspend,
 	.resume		= drm_log_client_resume,
-- 
2.51.1