[PATCH 6/7] Detaching fbcon: Add capability to attach/detach fbcon

[PATCH 6/7] Detaching fbcon: Add capability to attach/detach fbcon

[Antonino A. Daplas]

Add the ability to detach and attach the framebuffer console to and from
the vt layer. This is done by echo'ing any value to sysfs attributes located
in class/graphics/fbcon. The two attributes are:

      attach - bind fbcon to the vt layer
      detach - unbind fbcon from the vt layer

Once fbcon is detached from the vt layer, fbcon can be unloaded if compiled as
a module. This feature is quite useful for developers who work on the
framebuffer or console subsystem. This is also useful for users who want to
go to text mode or graphics mode without having to reboot.

Directly unloading the fbcon module is not possible because the vt layer
increments the module reference count for all bound consoles.  Detaching fbcon
decrements the module reference count to zero so unloading becomes possible.

Detaching fbcon may interfere with X and/or DRM.

Signed-off-by: Antonino Daplas <adaplas@pol.net>
---

 drivers/video/console/fbcon.c |  155 ++++++++++++++++++++++++++---------------
 1 files changed, 97 insertions(+), 58 deletions(-)

diff --git a/drivers/video/console/fbcon.c b/drivers/video/console/fbcon.c
index a8de822..b910eff 100644
--- a/drivers/video/console/fbcon.c
+++ b/drivers/video/console/fbcon.c
@@ -194,7 +194,8 @@ static void fbcon_redraw_move(struct vc_
 			      int line, int count, int dy);
 static void fbcon_modechanged(struct fb_info *info);
 static void fbcon_set_all_vcs(struct fb_info *info);
-
+static void fbcon_start(void);
+static void fbcon_exit(void);
 static struct class_device *fbcon_class_device;
 
 #ifdef CONFIG_MAC
@@ -391,15 +392,18 @@ static void fb_flashcursor(void *private
 	int c;
 	int mode;
 
-	if (ops->currcon != -1)
+	acquire_console_sem();
+	if (ops && ops->currcon != -1)
 		vc = vc_cons[ops->currcon].d;
 
 	if (!vc || !CON_IS_VISIBLE(vc) ||
 	    fbcon_is_inactive(vc, info) ||
  	    registered_fb[con2fb_map[vc->vc_num]] != info ||
-	    vc_cons[ops->currcon].d->vc_deccm != 1)
+	    vc_cons[ops->currcon].d->vc_deccm != 1) {
+		release_console_sem();
 		return;
-	acquire_console_sem();
+	}
+
 	p = &fb_display[vc->vc_num];
 	c = scr_readw((u16 *) vc->vc_pos);
 	mode = (!ops->cursor_flash || ops->cursor_state.enable) ?
@@ -2101,12 +2105,11 @@ static int fbcon_switch(struct vc_data *
 		if (info->fbops->fb_set_par)
 			info->fbops->fb_set_par(info);
 
-		if (old_info != info) {
+		if (old_info != info)
 			fbcon_del_cursor_timer(old_info);
-			fbcon_add_cursor_timer(info);
-		}
 	}
 
+	fbcon_add_cursor_timer(info);
 	set_blitting_type(vc, info);
 	ops->cursor_reset = 1;
 
@@ -2847,7 +2850,8 @@ static int fbcon_fb_registered(int idx)
 			ret = fbcon_takeover(1);
 	} else {
 		for (i = 0; i < MAX_NR_CONSOLES; i++) {
-			if (con2fb_map_boot[i] == idx)
+			if (con2fb_map_boot[i] == idx &&
+			    con2fb_map[i] == -1)
 				set_con2fb_map(i, idx, 0);
 		}
 	}
@@ -3046,9 +3050,32 @@ err:
 	return snprintf(buf, PAGE_SIZE, "%d\n", rotate);
 }
 
+static ssize_t store_attach(struct class_device *class_device,
+			    const char *buf, size_t count)
+{
+	if (info_idx == -1)
+		fbcon_start();
+
+	return count;
+}
+
+static ssize_t store_detach(struct class_device *class_device,
+			    const char *buf, size_t count)
+{
+	if (info_idx != -1) {
+		fbcon_exit();
+		give_up_console(&fb_con);
+	}
+
+	info_idx = -1;
+	return count;
+}
+
 static struct class_device_attribute class_device_attrs[] = {
 	__ATTR(rotate, S_IRUGO|S_IWUSR, show_rotate, store_rotate),
 	__ATTR(rotate_all, S_IWUSR, NULL, store_rotate_all),
+	__ATTR(attach, S_IWUSR, NULL, store_attach),
+	__ATTR(detach, S_IWUSR, NULL, store_detach),
 };
 
 static int fbcon_init_class_device(void)
@@ -3061,67 +3088,31 @@ static int fbcon_init_class_device(void)
 	return 0;
 }
 
-static int __init fb_console_init(void)
+static void fbcon_start(void)
 {
-	int i;
-
-	acquire_console_sem();
-	fb_register_client(&fbcon_event_notifier);
-	release_console_sem();
-
-	fbcon_class_device =
-	    class_device_create(fb_class, NULL,
-				MKDEV(FB_MAJOR, FB_MAX), NULL,
-				"fbcon");
-	if (IS_ERR(fbcon_class_device)) {
-	    printk(KERN_WARNING "Unable to create class_device "
-		   "for fbcon; errno = %ld\n",
-		   PTR_ERR(fbcon_class_device));
-	    fbcon_class_device = NULL;
-	} else
-	    fbcon_init_class_device();
+	if (num_registered_fb) {
+		int i;
 
-	for (i = 0; i < MAX_NR_CONSOLES; i++)
-		con2fb_map[i] = -1;
+		acquire_console_sem();
 
-	if (num_registered_fb) {
 		for (i = 0; i < FB_MAX; i++) {
 			if (registered_fb[i] != NULL) {
 				info_idx = i;
 				break;
 			}
 		}
+
+		release_console_sem();
 		fbcon_takeover(0);
 	}
-
-	return 0;
-}
-
-module_init(fb_console_init);
-
-#ifdef MODULE
-
-static void __exit fbcon_deinit_class_device(void)
-{
-	int i;
-
-	for (i = 0; i < ARRAY_SIZE(class_device_attrs); i++)
-		class_device_remove_file(fbcon_class_device,
-					 &class_device_attrs[i]);
 }
 
-static void __exit fbcon_exit(void)
+static void fbcon_exit(void)
 {
 	struct fb_info *info;
 	int i, j, mapped;
 
-	for (i = 0; i < FB_MAX; i++) {
-		info = registered_fb[i];
-
-		if (info && info->fbcon_par)
-			fbcon_del_cursor_timer(info);
-	}
-
+	acquire_console_sem();
 #ifdef CONFIG_ATARI
 	free_irq(IRQ_AUTO_4, fbcon_vbl_handler);
 #endif
@@ -3131,6 +3122,7 @@ #ifdef CONFIG_MAC
 #endif
 
 	kfree((void *)softback_buf);
+	softback_buf = 0UL;
 
 	for (i = 0; i < FB_MAX; i++) {
 		mapped = 0;
@@ -3150,22 +3142,69 @@ #endif
 			if (info->fbops->fb_release)
 				info->fbops->fb_release(info, 0);
 			module_put(info->fbops->owner);
-			kfree(info->fbcon_par);
-			info->fbcon_par = NULL;
+
+			if (info->fbcon_par) {
+				fbcon_del_cursor_timer(info);
+				kfree(info->fbcon_par);
+				info->fbcon_par = NULL;
+			}
+
+			if (info->queue.func == fb_flashcursor)
+				info->queue.func = NULL;
+
 		}
 	}
 
-	fbcon_deinit_class_device();
-	class_device_destroy(fb_class, MKDEV(FB_MAJOR, FB_MAX));
+	release_console_sem();
+}
+
+static int __init fb_console_init(void)
+{
+	int i;
+
+	acquire_console_sem();
+	fb_register_client(&fbcon_event_notifier);
+	fbcon_class_device =
+	    class_device_create(fb_class, NULL,
+				MKDEV(FB_MAJOR, FB_MAX), NULL,
+				"fbcon");
+
+	if (IS_ERR(fbcon_class_device)) {
+		printk(KERN_WARNING "Unable to create class_device "
+		       "for fbcon; errno = %ld\n",
+		       PTR_ERR(fbcon_class_device));
+		fbcon_class_device = NULL;
+	} else
+		fbcon_init_class_device();
+
+	for (i = 0; i < MAX_NR_CONSOLES; i++)
+		con2fb_map[i] = -1;
+
+	release_console_sem();
+	fbcon_start();
+	return 0;
+}
+
+module_init(fb_console_init);
+
+#ifdef MODULE
+
+static void fbcon_deinit_class_device(void)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(class_device_attrs); i++)
+		class_device_remove_file(fbcon_class_device,
+					 &class_device_attrs[i]);
 }
 
 static void __exit fb_console_exit(void)
 {
 	acquire_console_sem();
 	fb_unregister_client(&fbcon_event_notifier);
-	fbcon_exit();
+	fbcon_deinit_class_device();
+	class_device_destroy(fb_class, MKDEV(FB_MAJOR, FB_MAX));
 	release_console_sem();
-	give_up_console(&fb_con);
 }	
 
 module_exit(fb_console_exit);

Re: [PATCH 6/7] Detaching fbcon: Add capability to attach/detach fbcon

[Andrew Morton]

On Tue, 06 Jun 2006 19:09:00 +0800
"Antonino A. Daplas" <adaplas@gmail.com> wrote:

> Add the ability to detach and attach the framebuffer console to and from
> the vt layer. This is done by echo'ing any value to sysfs attributes located
> in class/graphics/fbcon. The two attributes are:
> 
>       attach - bind fbcon to the vt layer
>       detach - unbind fbcon from the vt layer

That's a bit unusual.  Normally a bind or unbind operation will operate
primarily upon the thing which is bound to, not upon the thing which is
bound.

I assume it makes sense this way, given the way the vt layer operates.  But
it rather rules out binding the fbcon layer to anything apart from the vt
layer (just thinking about it design-wise).

ummm, expressing it differently:

	echo "bind fbcon" > /sys/whatever/some-vt-file
	echo "unbind fbcon" > /sys/whatever/some-vt-file

would be more typical usage.

> Once fbcon is detached from the vt layer, fbcon can be unloaded if compiled as
> a module. This feature is quite useful for developers who work on the
> framebuffer or console subsystem. This is also useful for users who want to
> go to text mode or graphics mode without having to reboot.

Do we have a place where this can be documented?

> Directly unloading the fbcon module is not possible because the vt layer
> increments the module reference count for all bound consoles.  Detaching fbcon
> decrements the module reference count to zero so unloading becomes possible.

Right.  So the vt layer should be told to let go of the fbcon layer.  It's
a vt operation, not an fbcon one, yes?

Re: [PATCH 6/7] Detaching fbcon: Add capability to attach/detach fbcon

[Antonino A. Daplas]

Andrew Morton wrote:
> On Tue, 06 Jun 2006 19:09:00 +0800
> "Antonino A. Daplas" <adaplas@gmail.com> wrote:
> 
>> Add the ability to detach and attach the framebuffer console to and from
>> the vt layer. This is done by echo'ing any value to sysfs attributes located
>> in class/graphics/fbcon. The two attributes are:
>>
>>       attach - bind fbcon to the vt layer
>>       detach - unbind fbcon from the vt layer
> 
> That's a bit unusual.  Normally a bind or unbind operation will operate
> primarily upon the thing which is bound to, not upon the thing which is
> bound.

I'm not against this.

> 
> I assume it makes sense this way, given the way the vt layer operates.  But
> it rather rules out binding the fbcon layer to anything apart from the vt
> layer (just thinking about it design-wise).

The vt-layer is different in that the device themselves bind to it, not
the other way around.  As I've told Jon, if someone change the vt-layer so
it behaves in a standard way, I'm all for it (that someone is probably me).

But thinking about it, it is probably not very difficult to change the
vt-layer.  We just make the vt-layer keep a list of registered drivers. And 
we already have /sys/class/tty/console, so I can put the attribute there
for bind and unbind.

> 
> ummm, expressing it differently:
> 
> 	echo "bind fbcon" > /sys/whatever/some-vt-file
> 	echo "unbind fbcon" > /sys/whatever/some-vt-file
> 
> would be more typical usage.
> 
>> Once fbcon is detached from the vt layer, fbcon can be unloaded if compiled as
>> a module. This feature is quite useful for developers who work on the
>> framebuffer or console subsystem. This is also useful for users who want to
>> go to text mode or graphics mode without having to reboot.
> 
> Do we have a place where this can be documented?

In Documentation/fb/fbcon.txt.

> 
>> Directly unloading the fbcon module is not possible because the vt layer
>> increments the module reference count for all bound consoles.  Detaching fbcon
>> decrements the module reference count to zero so unloading becomes possible.
> 
> Right.  So the vt layer should be told to let go of the fbcon layer.  It's
> a vt operation, not an fbcon one, yes?

Yes. I'll take a stab at doing it this way. 

Tony