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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 <alan@linux.intel.com>
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 <daniel.vetter@ffwll.ch>
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 <daniel.vetter@intel.com>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
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Use mask 0x10 for "soft cursor" detection on in function tile_cursor.
(Tile Blitting Operation in framebuffer console).
The old mask 0x01 for vc_cursor_type detects CUR_NONE, CUR_LOWER_THIRD
and every second mode value as "software cursor". This hides the cursor
for these modes (cursor.mode = 0). But, only CUR_NONE or "software cursor"
should hide the cursor.
See also 0x10 in functions add_softcursor, bit_cursor and cw_cursor.
Signed-off-by: Henry Nestler <henry.nestler@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
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The current attr_fgcol_ec / attr_bgcol_ec macros do a simple shift of bits
to get the color from vc_video_erase_char. For a monochrome display
however the attribute does not contain any color, only attribute bits.
Furthermore the reverse bit is lost because it is shifted out, the
resulting color is always 0.
This can bee seen on a monochrome console either directly or by setting it
to inverse mode via "setterm -inversescreen on" . Text is written with
correct color, fb_fillrects from a bit_clear / bit_clear_margins will get
wrong colors.
Signed-off-by: Thomas Pfaff <tpfaff@pcs.com>
Cc: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Signed-off-by: Jörn Engel <joern@wohnheim.fh-wedel.de>
Signed-off-by: Adrian Bunk <bunk@stusta.de>
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Do not pass the structure display since fbcon is already keeping the pointer
to the current display.
Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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This patch series implements generic code to rotate the console at 90, 180,
and 270 degrees. The implementation is completely done in the framebuffer
console level, thus no changes to the framebuffer layer or to the drivers
are needed.
Console rotation is required by some Sharp-based devices where the natural
orientation of the display is not at 0 degrees. Also, users that have
displays that can pivot will benefit by having a console in portrait mode
if they so desire.
The choice to implement the code in the console layer rather than in the
framebuffer layer is due to the following reasons:
- it's fast
- it does not require driver changes
- it can coexist with devices that can rotate the display at the hardware level
- it complements graphics applications that can do display rotation
The changes to core fbcon are minimal-- recognition of the console
rotation angle so it can swap directions, origins and axes (xres vs yres,
xpanstep vs ypanstep, xoffset vs yoffset, etc) and storage of the rotation
angle per display. The bulk of the code that does the actual drawing to the
screen are placed in separate files. Each angle of rotation has separate
methods (bmove, clear, putcs, cursor, update_start which is derived from
update_var, and clear_margins). To mimimize processing time, the fontdata
are pre-rotated at each console switch (only if the font or the angle has
changed).
The option can be compiled out (CONFIG_FRAMEBUFFER_CONSOLE_ROTATION = n) if
rotation is not needed.
Choosing the rotation angle can be done in several ways:
1. boot option fbcon=rotate:n, where
n = 0 - normal
n = 1 - 90 degrees (clockwise)
n = 2 - 180 degrees (upside down)
n = 3 - 270 degrees (counterclockwise)
2. echo n > /sys/class/graphics/fb[num]/con_rotate
where n is the same as described above. It sets the angle of rotation
of the current console
3 echo n > /sys/class/graphics/fb[num]/con_rotate_all
where n is the same as described above. Globally sets the angle of
rotation.
GOTCHAS:
The option, especially at angles of 90 and 270 degrees, will exercise
the least used code of drivers. Namely, at these angles, panning is done
in the x-axis, so it can reveal bugs in the driver if xpanstep is set
incorrectly. A workaround is to set xpanstep = 0.
Secondly, at these angles, the framebuffer memory access can be
unaligned if (fontheight * bpp) % 32 ~= 0 which can reveal bugs in the drivers
imageblit, fillrect and copyarea functions. (I think cfbfillrect may have
this buglet). A workaround is to use a standard 8x16 font.
Speed:
The scrolling speed difference between 0 and 180 degrees is minimal,
somewhere areound 1-2%. At 90 or 270 degress, speed drops down to a vicinity
of 30-40%. This is understandable because the blit direction is across the
framebuffer "direction." Scrolling will be helped at these angles if xpanstep
is not equal to zero, use of 8x16 fonts, and setting xres_virtual >= xres * 2.
Note: The code is tested on little-endian only, so I don't know if it will
work in big-endian. Please let me know, it will take only less than a minute
of your time.
This patch prepares fbcon for console rotation and contains the following
changes:
- add rotate field in struct fbcon_ops to keep fbcon's current rotation
angle
- add con_rotate field in struct display to store per-display rotation angle
- create a private copy of the current var to fbcon. This will prevent
fbcon from directly manipulating info->var, especially the fields xoffset,
yoffset and vmode.
- add ability to swap pertinent axes (xres, yres; xpanstep, ypanstep; etc)
depending on the rotation angle
- change global update_var() (function that sets the screen start address)
as an fbcon method update_start. This is required because the axes, start
offset, and/or direction can be reversed depending on the rotation angle.
- add fbcon method rotate_font() which will rotate each character bitmap to
the correct angle of rotation.
- add fbcon boot option 'rotate' to select the angle of rotation at bootime.
Currently does nothing until all patches are applied.
Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
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