On Mon, Nov 08, 2021 at 04:34:53PM +0100, Jocelyn Falempe wrote:

When using Xorg/Logind and an external monitor connected with an MST dock. After disconnecting the external monitor, switching to VT may not work, the (internal) monitor sill display Xorg, and you can't see what you are typing in the VT.

This is related to commit e2809c7db818 ("drm/fb_helper: move deferred fb checking into restore mode (v2)")

When switching to VT, with Xorg and logind, if there are pending hotplug event (like MST unplugged), the hotplug path may not be fulfilled, because logind may drop the master a bit later. It leads to the console not showing up on the monitor.

So when dropping the drm master, call the delayed hotplug function if needed.

v2: rewrote the patch by calling the hotplug function after dropping master

Signed-off-by: Jocelyn Falempe jfalempe@redhat.com

Lastclose console restore is a very gross hack, and generally doesn't work well.

The way this is supposed to work is: - userspace drops drm master (because drm master always wins) - userspace switches the console back to text mode (which will restore the console)

I guess we could also do this from dropmaster once more (like from lastclose), but that really feels like papering over userspace bugs. And given what a massive mess this entire area is already, I'm not eager to add more hacks here.

So ... can't we fix userspace?

Ofc if it's a regression then that's different, but then I think we need a bit clearer implementation. I'm not clear on why you clear the callback (plus the locking looks busted). -Daniel

---

drivers/gpu/drm/drm_auth.c | 7 +++++++ drivers/gpu/drm/drm_fb_helper.c | 6 +++--- include/drm/drm_fb_helper.h | 4 +++- 3 files changed, 13 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c index 60a6b21474b1..73acf1994d49 100644 --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -35,6 +35,7 @@ #include <drm/drm_file.h> #include <drm/drm_lease.h> #include <drm/drm_print.h> +#include <drm/drm_fb_helper.h>

#include "drm_internal.h" #include "drm_legacy.h" @@ -321,6 +322,12 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data, }

drm_drop_master(dev, file_priv);

• mutex_unlock(&dev->master_mutex);
• if (dev->fb_helper && dev->fb_helper->delayed_hotplug)

• dev->fb_helper->delayed_hotplug(dev->fb_helper);
  

• return ret;

out_unlock: mutex_unlock(&dev->master_mutex); return ret; diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c index 8e7a124d6c5a..e8d8cc3f47c3 100644 --- a/drivers/gpu/drm/drm_fb_helper.c +++ b/drivers/gpu/drm/drm_fb_helper.c @@ -252,9 +252,9 @@ __drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper, ret = drm_client_modeset_commit(&fb_helper->client); }

• do_delayed = fb_helper->delayed_hotplug;

• do_delayed = (fb_helper->delayed_hotplug != NULL); if (do_delayed)

• fb_helper->delayed_hotplug = false;
  

• fb_helper->delayed_hotplug = NULL;
  

  mutex_unlock(&fb_helper->lock);

  if (do_delayed)

@@ -1966,7 +1966,7 @@ int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper) }

if (!fb_helper->fb || !drm_master_internal_acquire(fb_helper->dev)) {

• fb_helper->delayed_hotplug = true;
  

• fb_helper->delayed_hotplug = drm_fb_helper_hotplug_event;
  

  mutex_unlock(&fb_helper->lock); return err; }

diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h index 3af4624368d8..c2131d1a0e23 100644 --- a/include/drm/drm_fb_helper.h +++ b/include/drm/drm_fb_helper.h @@ -160,8 +160,10 @@ struct drm_fb_helper { * A hotplug was received while fbdev wasn't in control of the DRM * device, i.e. another KMS master was active. The output configuration * needs to be reprobe when fbdev is in control again.

• * NULL, or a pointer to the hotplug function, so it can be called
  

• * by the drm drop function directly.
  

  */

• bool delayed_hotplug;

• int (*delayed_hotplug)(struct drm_fb_helper *helper);

  /**

  • @deferred_setup:

-- 2.33.1