[PATCH v2] drm/mediatek: Remove all conflicting aperture devices during probe

[Luca Leonardo Scorcia]

If a device has a framebuffer available it might be already used as
display by simple-framebuffer or simpledrm when mediatek-drm is probed.
This is actually helpful when porting to a new device as
framebuffers are simple to setup in device trees and fbcon can be
used to monitor the kernel boot process.

When drm-mediatek loads a new fb device is initialized, however
fbcon remains attached to the initial framebuffer which is no longer
connected to the actual display - the early fb is never removed.

We can gracefully transition from framebuffer handling to drm-managed
display by calling aperture_remove_all_conflicting_devices before
registering mediatek-drm. This takes care of unloading other fb
devices/drivers and disconnects fbcon which then automatically
reconnects to mediatekdrmfb as soon as it's available.

The function is invoked just before drm_dev_register() to kick out
the existing framebuffer as late as possible to reduce the time the
screen is unresponsive.

Signed-off-by: Luca Leonardo Scorcia <l.scorcia@xxxxxxxxx>
---
v2: Moved the call to aperture_remove_all_conflicting_devices to 
    right before drm_dev_register()

 drivers/gpu/drm/mediatek/mtk_drm_drv.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
index a94c51a83261..02effd9fc698 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
@@ -4,6 +4,7 @@
  * Author: YT SHEN <yt.shen@xxxxxxxxxxxx>
  */
 
+#include <linux/aperture.h>
 #include <linux/component.h>
 #include <linux/module.h>
 #include <linux/of.h>
@@ -670,6 +671,10 @@ static int mtk_drm_bind(struct device *dev)
 	if (ret < 0)
 		goto err_free;
 
+	ret = aperture_remove_all_conflicting_devices(DRIVER_NAME);
+	if (ret < 0)
+		dev_err(dev, "Error %d while removing conflicting aperture devices", ret);
+
 	ret = drm_dev_register(drm, 0);
 	if (ret < 0)
 		goto err_deinit;
-- 
2.43.0