kernel/drivers/video/console/softcursor.c, branch linux-rolling-stable

fbcon: Make fbcon a built-time depency for fbdev

2017-08-01T15:32:07Z

There's a bunch of folks who're trying to make printk less contended and faster, but there's a problem: printk uses the console_lock, and the console lock has become the BKL for all things fbdev/fbcon, which in turn pulled in half the drm subsystem under that lock. That's awkward. There reasons for that is probably just a historical accident: - fbcon is a runtime option of fbdev, i.e. at runtime you can pick whether your fbdev driver instances are used as kernel consoles. Unfortunately this wasn't implemented with some module option, but through some module loading magic: As long as you don't load fbcon.ko, there's no fbdev console support, but loading it (in any order wrt fbdev drivers) will create console instances for all fbdev drivers. - This was implemented through a notifier chain. fbcon.ko enumerates all fbdev instances at load time and also registers itself as listener in the fbdev notifier. The fbdev core tries to register new fbdev instances with fbcon using the notifier. - On top of that the modifier chain is also used at runtime by the fbdev subsystem to e.g. control backlights for panels. - The problem is that the notifier puts a mutex locking context between fbdev and fbcon, which mixes up the locking contexts for both the runtime usage and the register time usage to notify fbcon. And at runtime fbcon (through the fbdev core) might call into the notifier from a printk critical section while console_lock is held. - This means console_lock must be an outer lock for the entire fbdev subsystem, which also means it must be acquired when registering a new framebuffer driver as the outermost lock since we might call into fbcon (through the notifier) which would result in a locking inversion if fbcon would acquire the console_lock from its notifier callback (which it needs to register the console). - console_lock can be held anywhere, since printk can be called anywhere, and through the above story, plus drm/kms being an fbdev driver, we pull in a shocking amount of locking hiercharchy underneath the console_lock. Which makes cleaning up printk really hard (not even splitting console_lock into an rwsem is all that useful due to this). There's various ways to address this, but the cleanest would be to make fbcon a compile-time option, where fbdev directly calls the fbcon register functions from register_framebuffer, or dummy static inline versions if fbcon is disabled. Maybe augmented with a runtime knob to disable fbcon, if that's needed (for debugging perhaps). But this could break some users who rely on the magic "loading fbcon.ko enables/disables fbdev framebuffers at runtime" thing, even if that's unlikely. Hence we must be careful: 1. Create a compile-time dependency between fbcon and fbdev in the least minimal way. This is what this patch does. 2. Wait at least 1 year to give possible users time to scream about how we broke their setup. Unlikely, since all distros make fbcon compile-in, and embedded platforms only compile stuff they know they need anyway. But still. 3. Convert the notifier to direct functions calls, with dummy static inlines if fbcon is disabled. We'll still need the fb notifier for the other uses (like backlights), but we can probably move it into the fb core (atm it must be built-into vmlinux). 4. Push console_lock down the call-chain, until it is down in console_register again. 5. Finally start to clean up and rework the printk/console locking. For context of this saga see commit 50e244cc793d511b86adea24972f3a7264cae114 Author: Alan Cox Date: Fri Jan 25 10:28:15 2013 +1000 fb: rework locking to fix lock ordering on takeover plus the pile of commits on top that tried to make this all work without terminally upsetting lockdep. We've uncovered all this when console_lock lockdep annotations where added in commit daee779718a319ff9f83e1ba3339334ac650bb22 Author: Daniel Vetter Date: Sat Sep 22 19:52:11 2012 +0200 console: implement lockdep support for console_lock On the patch itself: - Switch CONFIG_FRAMEBUFFER_CONSOLE to be a boolean, using the overall CONFIG_FB tristate to decided whether it should be a module or built-in. - At first I thought I could force the build depency with just a dummy symbol that fbcon.ko exports and fb.ko uses. But that leads to a module depency cycle (it works fine when built-in). Since this tight binding is the entire goal the simplest solution is to move all the fbcon modules (and there's a bunch of optinal source-files which are each modules of their own, for no good reason) into the overall fb.ko core module. That's a bit more than what I would have liked to do in this patch, but oh well. Signed-off-by: Daniel Vetter Cc: Alan Cox Cc: Sergey Senozhatsky Cc: Steven Rostedt Reviewed-by: Sean Paul Signed-off-by: Bartlomiej Zolnierkiewicz

drivers/video/console/softcursor.c: remove redundant NULL check before kfree()

2012-12-10T09:33:53Z

Signed-off-by: Sachin Kamat Cc: Florian Tobias Schandinat Cc: Tomi Valkeinen Signed-off-by: Andrew Morton Signed-off-by: Tomi Valkeinen

fbdev: change asm/uaccess.h to linux/uaccess.h

2007-10-16T16:43:17Z

This patch replaces with after the checkpatch.pl hint. The include of is removed if the driver does not use it. Signed-off-by: Krzysztof Helt Signed-off-by: Antonino Daplas Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

fix file specification in comments

2007-05-09T06:58:16Z

Many files include the filename at the beginning, serveral used a wrong one. Signed-off-by: Uwe Kleine-König Signed-off-by: Adrian Bunk

[PATCH] softcursor.c: avoid unaligned accesses

2006-12-08T16:29:07Z

Fix some possible unaligned accesses when accessing fields of 'image' pointer. Indeed this pointer was obtained by allocating a block of memory that embeds a temporary array plus an image structure. The temporary buffer was located at the start of the allocated block and depending on its size, the image structure which comes right after can be unaligned. For example when using mini fonts (4x6) (cursor's width is 4 and its height is 6) the temporary buf size is 6 bytes. Therefore this patch moves the image structure to the start of the block and moves the temporary buffer right after. It makes 'image' pointer always aligned and since the tempo buf is a buffer of char, it's always correctly aligned as well. It also fixes the file header alignement. Signed-off-by: Franck Bui-Huu Cc: James Simmons Cc: "Antonino A. Daplas" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

[PATCH] fbcon: Use persistent allocation for cursor blinking

2006-10-03T15:04:10Z

Every time the console cursor blinks, we do a kmalloc/kfree pair. This patch turns that into a single allocation. This allocation was the most frequent kmalloc I saw on my test box. [adaplas] Per Alan's suggestion, move global variables to fbcon's private structure. This would also avoid resource leaks when fbcon is unloaded. Signed-off-by: Dave Jones Acked-by: Alan Cox Signed-off-by: Antonino Daplas Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

[PATCH] vt: Remove VT-specific declarations and definitions from tty.h

2006-07-10T20:24:16Z

MAX_NR_CONSOLES, fg_console, want_console and last_console are more of a function of the VT layer than the TTY one. Moving these to vt.h and vt_kern.h allows all of the framebuffer and VT console drivers to remove their dependency on tty.h. [akpm@osdl.org: fix alpha build] Signed-off-by: Jon Smirl Signed-off-by: Antonino Daplas Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

[PATCH] drivers/video/: possible cleanups

2006-01-10T16:01:56Z

This patch contains the possible cleanups including the following: - every file should #include the headers containing the prototypes for it's global functions - make needlessly global functions static - kyro/STG4000Interface.h: #include video/kyro.h and linux/pci.h instead of a manual "struct pci_dev" - i810_main.{c,h}: prototypes for static functions belong to the C file Signed-off-by: Adrian Bunk Acked-by: "Antonino A. Daplas" Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

[PATCH] fbcon/fbdev: Move softcursor out of fbdev to fbcon

2005-11-07T15:53:50Z

According to Jon Smirl, filling in the field fb_cursor with soft_cursor for drivers that do not support hardware cursors is redundant. The soft_cursor function is usable by all drivers because it is just a wrapper around fb_imageblit. And because soft_cursor is an fbcon-specific hook, the file is moved to the console directory. Thus, drivers that do not support hardware cursors can leave the fb_cursor field blank. For drivers that do, they can fill up this field with their own version. The end result is a smaller code size. And if the framebuffer console is not loaded, module/kernel size is also reduced because the soft_cursor module will also not be loaded. Signed-off-by: Antonino Daplas Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds