VT console blank ignored by DRM drivers on QEMU

[Takashi Iwai]

On Mon, 10 Jul 2017 13:47:57 +0200,
Gerd Hoffmann wrote:
> 
>   Hi,
> 
> > But aside from that, can't we just teach these drivers to properly do
> > dpms? With the atomic framework dpms is implement as simply turning
> > the screen off, any driver should be able to support that properly.
> 
> Well, the virtual hardware simply has no dpms support, except maybe for
> cirrus which mimics physical hardware.
> 
> bochs could toggle the blank bit in vga register space.
> 
> virtio and qxl could unmap the plane, but that might have unwanted
> effects on the host side because qemu thinks the guest turned off the
> display altogether.
> 
> > For the fbcon issue, can we perhaps just unconditionally ask fbcon to
> > clear the screen when blanking? It's not really perf critical, so
> > doing that for everyone shouldn't hurt.
> 
> Sounds good to me.
> 
> I've seen this on real hardware too btw (arm board with non-working
> dpms).

So something like below?
(Adding Bartlomiej to Cc, as it's fbcon stuff)


Takashi

-- 8< --
From: Takashi Iwai <tiwai at suse.de>
Subject: [PATCH] fbcon: Perform generic blank unconditionally

Currently fbcon performs the manual clearance of console as a fallback
only when fb_blank() returns an error.  Unfortunately, all DRM fbcons
running on QEMU don't return the error but only adjust the non-working
DPMS, we end up just having the frozen screen upon blank call.
Also Gerd suggested that a similar issue could have seen on the bare
metal, too.

As a simple workaround suggested by Daniel, let's call
fbcon_generic_blank() unconditionally at fbcon_blank() so that it
always clears the console.

Suggested-by: Daniel Vetter <daniel at ffwll.ch>
Cc: Gerd Hoffmann <kraxel at redhat.com>
Cc: Alexander Graf <agraf at suse.de>
Signed-off-by: Takashi Iwai <tiwai at suse.de>
---
 drivers/video/console/fbcon.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
index 12ded23f1aaf..65169a5a1bca 100644
--- a/drivers/video/console/fbcon.c
+++ b/drivers/video/console/fbcon.c
@@ -2347,8 +2347,8 @@ static int fbcon_blank(struct vc_data *vc, int blank, int mode_switch)
 			ops->cursor_flash = (!blank);
 
 			if (!(info->flags & FBINFO_MISC_USEREVENT))
-				if (fb_blank(info, blank))
-					fbcon_generic_blank(vc, info, blank);
+				fb_blank(info, blank);
+				fbcon_generic_blank(vc, info, blank);
 		}
 
 		if (!blank)
-- 
2.13.2