Re: console.c unblank_screen problem

[Mikael Pettersson]

On Sun, 25 Mar 2001 18:40:03 +0200, Benjamin Herrenschmidt wrote:

>There is a problem with the power management code for console.c
>
>The current code calls do_blank_screen(0); on PM_SUSPEND, and
>unblank_screen() on PM_RESUME.
>
>The problem happens when X is the current display while putting the
>machine to sleep. The do_blank_screen(0) code will do nothing as
>the console is not in KD_TEXT mode.
>However, unblank_screen has no such protection. That means that
>on wakeup, the cursor timer & console blank timers will be re-enabled
>while X is frontmost, causing the blinking cursor to be displayed on
>top of X, and other possible issues.
>
>I hacked the following pacth to work around this. It appear to work
>fine, but since the console code is pretty complex, I'm not sure about
>possible side effects and I'd like some comments before submiting it
>to Linus:

Thanks for this patch. I've been using it on my Dell Latitude laptop
for the last 10 days, and it has been a significant improvement.

Before the patch: After a few days with a 2.4 kernel and RH7.0
(XFree86-4.0.1-1 and XFree86-SVGA-3.3.6-33) the latop would
misbehave at a resume event: when I opened the lid the screen would
unblank and then after less than a second the entire screen would
shift (wrap/rotate) left by about 40% of its width. Restarting X
would only fix this temporarily, as the next resume would have the
same problem. This does not occur with a 2.2 kernel or with the
Accelerated-X server I used before.

With the patch: No problem after 10 days with frequent suspend/resume
cycles. (2.4.2-ac24 + the patch)

[Alan, mind putting this in the next 2.4.3-ac? I've rediffed it
against 2.4.3-ac2.]

/Mikael

--- linux-2.4.3-ac2/drivers/char/console.c.~1~	Wed Apr  4 12:15:28 2001
+++ linux-2.4.3-ac2/drivers/char/console.c	Wed Apr  4 12:29:01 2001
@@ -2713,12 +2713,16 @@
 		printk("unblank_screen: tty %d not allocated ??\n", fg_console+1);
 		return;
 	}
+	currcons = fg_console;
+	if (vcmode != KD_TEXT) {
+		console_blanked = 0;
+		return;
+	}
 	console_timer.function = blank_screen;
 	if (blankinterval) {
 		mod_timer(&console_timer, jiffies + blankinterval);
 	}
 
-	currcons = fg_console;
 	console_blanked = 0;
 	if (console_blank_hook)
 		console_blank_hook(0);