diff mbox series

[1/3] fbcon: Disable accelerated scrolling

Message ID 20201029101428.4058311-1-daniel.vetter@ffwll.ch (mailing list archive)
State New, archived
Headers show
Series [1/3] fbcon: Disable accelerated scrolling | expand

Commit Message

Daniel Vetter Oct. 29, 2020, 10:14 a.m. UTC 
So ever since syzbot discovered fbcon, we have solid proof that it's
full of bugs. And often the solution is to just delete code and remove
features, e.g.  50145474f6ef ("fbcon: remove soft scrollback code").

Now the problem is that most modern-ish drivers really only treat
fbcon as an dumb kernel console until userspace takes over, and Oops
printer for some emergencies. Looking at drm drivers and the basic
vesa/efi fbdev drivers shows that only 3 drivers support any kind of
acceleration:

- nouveau, seems to be enabled by default
- omapdrm, when a DMM remapper exists using remapper rewriting for
  y/xpanning
- gma500, but that is getting deleted now for the GTT remapper trick,
  and the accelerated copyarea never set the FBINFO_HWACCEL_COPYAREA
  flag, so unused (and could be deleted already I think).

No other driver supportes accelerated fbcon. And fbcon is the only
user of this accel code (it's not exposed as uapi through ioctls),
which means we could garbage collect fairly enormous amounts of code
if we kill this.

Plus because syzbot only runs on virtual hardware, and none of the
drivers for that have acceleration, we'd remove a huge gap in testing.
And there's no other even remotely comprehensive testing aside from
syzbot.

This patch here just disables the acceleration code by always
redrawing when scrolling. The plan is that once this has been merged
for well over a year in released kernels, we can start to go around
and delete a lot of code.

v2:
- Drop a few more unused local variables, somehow I missed the
compiler warnings (Sam)
- Fix typo in comment (Jiri)
- add a todo entry for the cleanup (Thomas)

Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Ben Skeggs <bskeggs@redhat.com>
Cc: nouveau@lists.freedesktop.org
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Peilin Ye <yepeilin.cs@gmail.com>
Cc: George Kennedy <george.kennedy@oracle.com>
Cc: Nathan Chancellor <natechancellor@gmail.com>
Cc: Peter Rosin <peda@axentia.se>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
---
 Documentation/gpu/todo.rst       | 18 ++++++++++++++
 drivers/video/fbdev/core/fbcon.c | 42 ++++++--------------------------
 2 files changed, 25 insertions(+), 35 deletions(-)

Comments

kernel test robot Oct. 29, 2020, 12:42 p.m. UTC | #1 
Hi Daniel,

I love your patch! Perhaps something to improve:

[auto build test WARNING on drm-intel/for-linux-next]
[also build test WARNING on drm-tip/drm-tip drm-exynos/exynos-drm-next tegra-drm/drm/tegra/for-next linus/master drm/drm-next v5.10-rc1 next-20201028]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch]

url:    https://github.com/0day-ci/linux/commits/Daniel-Vetter/fbcon-Disable-accelerated-scrolling/20201029-181618
base:   git://anongit.freedesktop.org/drm-intel for-linux-next
config: sparc64-randconfig-r005-20201029 (attached as .config)
compiler: sparc64-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/0day-ci/linux/commit/b457f0ea024ca7202fa63f5a94f9d5abf65529f8
        git remote add linux-review https://github.com/0day-ci/linux
        git fetch --no-tags linux-review Daniel-Vetter/fbcon-Disable-accelerated-scrolling/20201029-181618
        git checkout b457f0ea024ca7202fa63f5a94f9d5abf65529f8
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=sparc64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kernel test robot <lkp@intel.com>

All warnings (new ones prefixed by >>):

   drivers/video/fbdev/core/fbcon.c: In function 'fbcon_init':
>> drivers/video/fbdev/core/fbcon.c:1089:6: warning: variable 'cap' set but not used [-Wunused-but-set-variable]
    1089 |  int cap, ret;
         |      ^~~
   drivers/video/fbdev/core/fbcon.c: In function 'fbcon_exit':
   drivers/video/fbdev/core/fbcon.c:3646:7: warning: variable 'pending' set but not used [-Wunused-but-set-variable]
    3646 |   int pending = 0;
         |       ^~~~~~~

vim +/cap +1089 drivers/video/fbdev/core/fbcon.c

^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1080  
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1081  static void fbcon_init(struct vc_data *vc, int init)
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1082  {
1f4ed2fb01f80f drivers/video/fbdev/core/fbcon.c Daniel Vetter             2019-05-28  1083  	struct fb_info *info;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1084  	struct fbcon_ops *ops;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1085  	struct vc_data **default_mode = vc->vc_display_fg;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1086  	struct vc_data *svc = *default_mode;
50233393f0cf9b drivers/video/fbdev/core/fbcon.c Daniel Vetter             2019-05-28  1087  	struct fbcon_display *t, *p = &fb_display[vc->vc_num];
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1088  	int logo = 1, new_rows, new_cols, rows, cols, charcnt = 256;
0fcf6ada2b8eb4 drivers/video/console/fbcon.c    Florian Tobias Schandinat 2009-09-22 @1089  	int cap, ret;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1090  
1f4ed2fb01f80f drivers/video/fbdev/core/fbcon.c Daniel Vetter             2019-05-28  1091  	if (WARN_ON(info_idx == -1))
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1092  	    return;
306958e8e8d150 drivers/video/console/fbcon.c    Adrian Bunk               2005-05-01  1093  
1f4ed2fb01f80f drivers/video/fbdev/core/fbcon.c Daniel Vetter             2019-05-28  1094  	if (con2fb_map[vc->vc_num] == -1)
1f4ed2fb01f80f drivers/video/fbdev/core/fbcon.c Daniel Vetter             2019-05-28  1095  		con2fb_map[vc->vc_num] = info_idx;
1f4ed2fb01f80f drivers/video/fbdev/core/fbcon.c Daniel Vetter             2019-05-28  1096  
1f4ed2fb01f80f drivers/video/fbdev/core/fbcon.c Daniel Vetter             2019-05-28  1097  	info = registered_fb[con2fb_map[vc->vc_num]];
306958e8e8d150 drivers/video/console/fbcon.c    Adrian Bunk               2005-05-01  1098  	cap = info->flags;
306958e8e8d150 drivers/video/console/fbcon.c    Adrian Bunk               2005-05-01  1099  
3c5a1b111373e6 drivers/video/fbdev/core/fbcon.c Andreas Schwab            2019-05-06  1100  	if (logo_shown < 0 && console_loglevel <= CONSOLE_LOGLEVEL_QUIET)
10993504d64735 drivers/video/fbdev/core/fbcon.c Prarit Bhargava           2019-02-08  1101  		logo_shown = FBCON_LOGO_DONTSHOW;
10993504d64735 drivers/video/fbdev/core/fbcon.c Prarit Bhargava           2019-02-08  1102  
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1103  	if (vc != svc || logo_shown == FBCON_LOGO_DONTSHOW ||
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1104  	    (info->fix.type == FB_TYPE_TEXT))
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1105  		logo = 0;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1106  
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1107  	if (var_to_display(p, &info->var, info))
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1108  		return;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1109  
d1baa4ffa677bf drivers/video/console/fbcon.c    Antonino A. Daplas        2007-07-17  1110  	if (!info->fbcon_par)
d1baa4ffa677bf drivers/video/console/fbcon.c    Antonino A. Daplas        2007-07-17  1111  		con2fb_acquire_newinfo(vc, info, vc->vc_num, -1);
d1baa4ffa677bf drivers/video/console/fbcon.c    Antonino A. Daplas        2007-07-17  1112  
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1113  	/* If we are not the first console on this
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1114  	   fb, copy the font from that console */
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1115  	t = &fb_display[fg_console];
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1116  	if (!p->fontdata) {
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1117  		if (t->fontdata) {
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1118  			struct vc_data *fvc = vc_cons[fg_console].d;
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1119  
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1120  			vc->vc_font.data = (void *)(p->fontdata =
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1121  						    fvc->vc_font.data);
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1122  			vc->vc_font.width = fvc->vc_font.width;
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1123  			vc->vc_font.height = fvc->vc_font.height;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1124  			p->userfont = t->userfont;
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1125  
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1126  			if (p->userfont)
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1127  				REFCOUNT(p->fontdata)++;
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1128  		} else {
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1129  			const struct font_desc *font = NULL;
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1130  
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1131  			if (!fontname[0] || !(font = find_font(fontname)))
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1132  				font = get_default_font(info->var.xres,
2d2699d9849248 drivers/video/console/fbcon.c    Antonino A. Daplas        2007-05-08  1133  							info->var.yres,
2d2699d9849248 drivers/video/console/fbcon.c    Antonino A. Daplas        2007-05-08  1134  							info->pixmap.blit_x,
2d2699d9849248 drivers/video/console/fbcon.c    Antonino A. Daplas        2007-05-08  1135  							info->pixmap.blit_y);
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1136  			vc->vc_font.width = font->width;
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1137  			vc->vc_font.height = font->height;
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1138  			vc->vc_font.data = (void *)(p->fontdata = font->data);
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1139  			vc->vc_font.charcount = 256; /* FIXME  Need to
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1140  							support more fonts */
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1141  		}
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1142  	}
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1143  
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1144  	if (p->userfont)
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1145  		charcnt = FNTCHARCNT(p->fontdata);
e614b18dcedb24 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-06-26  1146  
b8c909454f046b drivers/video/console/fbcon.c    Antonino A. Daplas        2005-09-09  1147  	vc->vc_can_do_color = (fb_get_color_depth(&info->var, &info->fix)!=1);
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1148  	vc->vc_complement_mask = vc->vc_can_do_color ? 0x7700 : 0x0800;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1149  	if (charcnt == 256) {
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1150  		vc->vc_hi_font_mask = 0;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1151  	} else {
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1152  		vc->vc_hi_font_mask = 0x100;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1153  		if (vc->vc_can_do_color)
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1154  			vc->vc_complement_mask <<= 1;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1155  	}
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1156  
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1157  	if (!*svc->vc_uni_pagedir_loc)
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1158  		con_set_default_unimap(svc);
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1159  	if (!*vc->vc_uni_pagedir_loc)
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1160  		con_copy_unimap(vc, svc);
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1161  
e4fc27618b7523 drivers/video/console/fbcon.c    Antonino A. Daplas        2005-11-08  1162  	ops = info->fbcon_par;
f235f664a8afab drivers/video/console/fbcon.c    Scot Doyle                2015-10-09  1163  	ops->cur_blink_jiffies = msecs_to_jiffies(vc->vc_cur_blink_ms);
c9e6a36492504e drivers/video/fbdev/core/fbcon.c Hans de Goede             2017-11-25  1164  
2428e59b530928 drivers/video/console/fbcon.c    Marcin Slusarz            2008-02-06  1165  	p->con_rotate = initial_rotation;
c9e6a36492504e drivers/video/fbdev/core/fbcon.c Hans de Goede             2017-11-25  1166  	if (p->con_rotate == -1)
c9e6a36492504e drivers/video/fbdev/core/fbcon.c Hans de Goede             2017-11-25  1167  		p->con_rotate = info->fbcon_rotate_hint;
c9e6a36492504e drivers/video/fbdev/core/fbcon.c Hans de Goede             2017-11-25  1168  	if (p->con_rotate == -1)
f2f4946b0adfd6 drivers/video/fbdev/core/fbcon.c Hans de Goede             2017-11-25  1169  		p->con_rotate = FB_ROTATE_UR;
c9e6a36492504e drivers/video/fbdev/core/fbcon.c Hans de Goede             2017-11-25  1170  
b73deed32d0874 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-01-09  1171  	set_blitting_type(vc, info);
e4fc27618b7523 drivers/video/console/fbcon.c    Antonino A. Daplas        2005-11-08  1172  
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1173  	cols = vc->vc_cols;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1174  	rows = vc->vc_rows;
e4fc27618b7523 drivers/video/console/fbcon.c    Antonino A. Daplas        2005-11-08  1175  	new_cols = FBCON_SWAP(ops->rotate, info->var.xres, info->var.yres);
e4fc27618b7523 drivers/video/console/fbcon.c    Antonino A. Daplas        2005-11-08  1176  	new_rows = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres);
e4fc27618b7523 drivers/video/console/fbcon.c    Antonino A. Daplas        2005-11-08  1177  	new_cols /= vc->vc_font.width;
e4fc27618b7523 drivers/video/console/fbcon.c    Antonino A. Daplas        2005-11-08  1178  	new_rows /= vc->vc_font.height;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1179  
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1180  	/*
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1181  	 * We must always set the mode. The mode of the previous console
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1182  	 * driver could be in the same resolution but we are using different
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1183  	 * hardware so we have to initialize the hardware.
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1184  	 *
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1185  	 * We need to do it in fbcon_init() to prevent screen corruption.
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1186  	 */
6ca8dfd78187d8 drivers/video/console/fbcon.c    Jiri Slaby                2016-06-23  1187  	if (con_is_visible(vc) && vc->vc_mode == KD_TEXT) {
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1188  		if (info->fbops->fb_set_par &&
0fcf6ada2b8eb4 drivers/video/console/fbcon.c    Florian Tobias Schandinat 2009-09-22  1189  		    !(ops->flags & FBCON_FLAGS_INIT)) {
0fcf6ada2b8eb4 drivers/video/console/fbcon.c    Florian Tobias Schandinat 2009-09-22  1190  			ret = info->fbops->fb_set_par(info);
0fcf6ada2b8eb4 drivers/video/console/fbcon.c    Florian Tobias Schandinat 2009-09-22  1191  
0fcf6ada2b8eb4 drivers/video/console/fbcon.c    Florian Tobias Schandinat 2009-09-22  1192  			if (ret)
0fcf6ada2b8eb4 drivers/video/console/fbcon.c    Florian Tobias Schandinat 2009-09-22  1193  				printk(KERN_ERR "fbcon_init: detected "
0fcf6ada2b8eb4 drivers/video/console/fbcon.c    Florian Tobias Schandinat 2009-09-22  1194  					"unhandled fb_set_par error, "
0fcf6ada2b8eb4 drivers/video/console/fbcon.c    Florian Tobias Schandinat 2009-09-22  1195  					"error code %d\n", ret);
0fcf6ada2b8eb4 drivers/video/console/fbcon.c    Florian Tobias Schandinat 2009-09-22  1196  		}
0fcf6ada2b8eb4 drivers/video/console/fbcon.c    Florian Tobias Schandinat 2009-09-22  1197  
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1198  		ops->flags |= FBCON_FLAGS_INIT;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1199  	}
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1200  
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1201  	ops->graphics = 0;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1202  
b457f0ea024ca7 drivers/video/fbdev/core/fbcon.c Daniel Vetter             2020-10-29  1203  	/*
b457f0ea024ca7 drivers/video/fbdev/core/fbcon.c Daniel Vetter             2020-10-29  1204  	 * No more hw acceleration for fbcon.
b457f0ea024ca7 drivers/video/fbdev/core/fbcon.c Daniel Vetter             2020-10-29  1205  	 *
b457f0ea024ca7 drivers/video/fbdev/core/fbcon.c Daniel Vetter             2020-10-29  1206  	 * FIXME: Garbage collect all the now dead code after sufficient time
b457f0ea024ca7 drivers/video/fbdev/core/fbcon.c Daniel Vetter             2020-10-29  1207  	 * has passed.
b457f0ea024ca7 drivers/video/fbdev/core/fbcon.c Daniel Vetter             2020-10-29  1208  	 */
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1209  	p->scrollmode = SCROLL_REDRAW;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1210  
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1211  	/*
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1212  	 *  ++guenther: console.c:vc_allocate() relies on initializing
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1213  	 *  vc_{cols,rows}, but we must not set those if we are only
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1214  	 *  resizing the console.
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1215  	 */
0035fe00f77d2b drivers/video/console/fbcon.c    Johannes Weiner           2009-08-06  1216  	if (init) {
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1217  		vc->vc_cols = new_cols;
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1218  		vc->vc_rows = new_rows;
0035fe00f77d2b drivers/video/console/fbcon.c    Johannes Weiner           2009-08-06  1219  	} else
0035fe00f77d2b drivers/video/console/fbcon.c    Johannes Weiner           2009-08-06  1220  		vc_resize(vc, new_cols, new_rows);
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1221  
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1222  	if (logo)
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1223  		fbcon_prepare_logo(vc, info, cols, rows, new_cols, new_rows);
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1224  
4d9c5b6eb42d9e drivers/video/console/fbcon.c    Antonino A. Daplas        2005-11-07  1225  	if (vc == svc && softback_buf)
4d9c5b6eb42d9e drivers/video/console/fbcon.c    Antonino A. Daplas        2005-11-07  1226  		fbcon_update_softback(vc);
e4fc27618b7523 drivers/video/console/fbcon.c    Antonino A. Daplas        2005-11-08  1227  
b73deed32d0874 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-01-09  1228  	if (ops->rotate_font && ops->rotate_font(info, vc)) {
e4fc27618b7523 drivers/video/console/fbcon.c    Antonino A. Daplas        2005-11-08  1229  		ops->rotate = FB_ROTATE_UR;
b73deed32d0874 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-01-09  1230  		set_blitting_type(vc, info);
e4fc27618b7523 drivers/video/console/fbcon.c    Antonino A. Daplas        2005-11-08  1231  	}
e4fc27618b7523 drivers/video/console/fbcon.c    Antonino A. Daplas        2005-11-08  1232  
1a37d5f51020b9 drivers/video/console/fbcon.c    Antonino A. Daplas        2006-03-31  1233  	ops->p = &fb_display[fg_console];
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1234  }
^1da177e4c3f41 drivers/video/console/fbcon.c    Linus Torvalds            2005-04-16  1235  

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all@lists.01.org
Thomas Zimmermann Oct. 29, 2020, 7:17 p.m. UTC | #2 
Am 29.10.20 um 11:14 schrieb Daniel Vetter:
> So ever since syzbot discovered fbcon, we have solid proof that it's
> full of bugs. And often the solution is to just delete code and remove
> features, e.g.  50145474f6ef ("fbcon: remove soft scrollback code").
> 
> Now the problem is that most modern-ish drivers really only treat
> fbcon as an dumb kernel console until userspace takes over, and Oops
> printer for some emergencies. Looking at drm drivers and the basic
> vesa/efi fbdev drivers shows that only 3 drivers support any kind of
> acceleration:
> 
> - nouveau, seems to be enabled by default
> - omapdrm, when a DMM remapper exists using remapper rewriting for
>   y/xpanning
> - gma500, but that is getting deleted now for the GTT remapper trick,
>   and the accelerated copyarea never set the FBINFO_HWACCEL_COPYAREA
>   flag, so unused (and could be deleted already I think).
> 
> No other driver supportes accelerated fbcon. And fbcon is the only
> user of this accel code (it's not exposed as uapi through ioctls),
> which means we could garbage collect fairly enormous amounts of code
> if we kill this.
> 
> Plus because syzbot only runs on virtual hardware, and none of the
> drivers for that have acceleration, we'd remove a huge gap in testing.
> And there's no other even remotely comprehensive testing aside from
> syzbot.
> 
> This patch here just disables the acceleration code by always
> redrawing when scrolling. The plan is that once this has been merged
> for well over a year in released kernels, we can start to go around
> and delete a lot of code.
> 
> v2:
> - Drop a few more unused local variables, somehow I missed the
> compiler warnings (Sam)
> - Fix typo in comment (Jiri)
> - add a todo entry for the cleanup (Thomas)

Thanks :)

> 
> Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Acked-by: Sam Ravnborg <sam@ravnborg.org>
> Cc: Jiri Slaby <jirislaby@kernel.org>
> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
> Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> Cc: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Ben Skeggs <bskeggs@redhat.com>
> Cc: nouveau@lists.freedesktop.org
> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Jiri Slaby <jirislaby@kernel.org>
> Cc: "Gustavo A. R. Silva" <gustavoars@kernel.org>
> Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> Cc: Peilin Ye <yepeilin.cs@gmail.com>
> Cc: George Kennedy <george.kennedy@oracle.com>
> Cc: Nathan Chancellor <natechancellor@gmail.com>
> Cc: Peter Rosin <peda@axentia.se>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> ---
>  Documentation/gpu/todo.rst       | 18 ++++++++++++++
>  drivers/video/fbdev/core/fbcon.c | 42 ++++++--------------------------
>  2 files changed, 25 insertions(+), 35 deletions(-)
> 
> diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
> index 6b224ef14455..bec99341a904 100644
> --- a/Documentation/gpu/todo.rst
> +++ b/Documentation/gpu/todo.rst
> @@ -277,6 +277,24 @@ Contact: Daniel Vetter, Noralf Tronnes
>  
>  Level: Advanced
>  
> +Garbage collect fbdev scrolling acceleration
> +--------------------------------------------
> +
> +Scroll acceleration is disabled in fbcon by hard-wiring p->scrollmode =
> +SCROLL_REDRAW. There's a ton of code this will allow us to remove:
> +- lots of code in fbcon.c
> +- a bunch of the hooks in fbcon_ops, maybe the remaining hooks could be called
> +  directly instead of the function table (with a switch on p->rotate)
> +- fb_copyarea is unused after this, and can be deleted from all drivers
> +
> +Note that not all acceleration code can be deleted, since clearing and cursor
> +support is still accelerated, which might be good candidates for further
> +deletion projects.
> +
> +Contact: Daniel Vetter
> +
> +Level: Intermediate
> +
>  idr_init_base()
>  ---------------
>  
> diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
> index cef437817b0d..a68253485244 100644
> --- a/drivers/video/fbdev/core/fbcon.c
> +++ b/drivers/video/fbdev/core/fbcon.c
> @@ -1147,11 +1147,13 @@ static void fbcon_init(struct vc_data *vc, int init)
>  
>  	ops->graphics = 0;
>  
> -	if ((cap & FBINFO_HWACCEL_COPYAREA) &&
> -	    !(cap & FBINFO_HWACCEL_DISABLED))
> -		p->scrollmode = SCROLL_MOVE;
> -	else /* default to something safe */
> -		p->scrollmode = SCROLL_REDRAW;
> +	/*
> +	 * No more hw acceleration for fbcon.
> +	 *
> +	 * FIXME: Garbage collect all the now dead code after sufficient time
> +	 * has passed.
> +	 */
> +	p->scrollmode = SCROLL_REDRAW;
>  
>  	/*
>  	 *  ++guenther: console.c:vc_allocate() relies on initializing
> @@ -1961,45 +1963,15 @@ static void updatescrollmode(struct fbcon_display *p,
>  {
>  	struct fbcon_ops *ops = info->fbcon_par;
>  	int fh = vc->vc_font.height;
> -	int cap = info->flags;
> -	u16 t = 0;
> -	int ypan = FBCON_SWAP(ops->rotate, info->fix.ypanstep,
> -				  info->fix.xpanstep);
> -	int ywrap = FBCON_SWAP(ops->rotate, info->fix.ywrapstep, t);
>  	int yres = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres);
>  	int vyres = FBCON_SWAP(ops->rotate, info->var.yres_virtual,
>  				   info->var.xres_virtual);
> -	int good_pan = (cap & FBINFO_HWACCEL_YPAN) &&
> -		divides(ypan, vc->vc_font.height) && vyres > yres;
> -	int good_wrap = (cap & FBINFO_HWACCEL_YWRAP) &&
> -		divides(ywrap, vc->vc_font.height) &&
> -		divides(vc->vc_font.height, vyres) &&
> -		divides(vc->vc_font.height, yres);
> -	int reading_fast = cap & FBINFO_READS_FAST;
> -	int fast_copyarea = (cap & FBINFO_HWACCEL_COPYAREA) &&
> -		!(cap & FBINFO_HWACCEL_DISABLED);
> -	int fast_imageblit = (cap & FBINFO_HWACCEL_IMAGEBLIT) &&
> -		!(cap & FBINFO_HWACCEL_DISABLED);
>  
>  	p->vrows = vyres/fh;
>  	if (yres > (fh * (vc->vc_rows + 1)))
>  		p->vrows -= (yres - (fh * vc->vc_rows)) / fh;
>  	if ((yres % fh) && (vyres % fh < yres % fh))
>  		p->vrows--;
> -
> -	if (good_wrap || good_pan) {
> -		if (reading_fast || fast_copyarea)
> -			p->scrollmode = good_wrap ?
> -				SCROLL_WRAP_MOVE : SCROLL_PAN_MOVE;
> -		else
> -			p->scrollmode = good_wrap ? SCROLL_REDRAW :
> -				SCROLL_PAN_REDRAW;
> -	} else {
> -		if (reading_fast || (fast_copyarea && !fast_imageblit))
> -			p->scrollmode = SCROLL_MOVE;
> -		else
> -			p->scrollmode = SCROLL_REDRAW;
> -	}
>  }
>  
>  #define PITCH(w) (((w) + 7) >> 3)
>
diff mbox series

Patch

diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
index 6b224ef14455..bec99341a904 100644
--- a/Documentation/gpu/todo.rst
+++ b/Documentation/gpu/todo.rst
@@ -277,6 +277,24 @@  Contact: Daniel Vetter, Noralf Tronnes
 
 Level: Advanced
 
+Garbage collect fbdev scrolling acceleration
+--------------------------------------------
+
+Scroll acceleration is disabled in fbcon by hard-wiring p->scrollmode =
+SCROLL_REDRAW. There's a ton of code this will allow us to remove:
+- lots of code in fbcon.c
+- a bunch of the hooks in fbcon_ops, maybe the remaining hooks could be called
+  directly instead of the function table (with a switch on p->rotate)
+- fb_copyarea is unused after this, and can be deleted from all drivers
+
+Note that not all acceleration code can be deleted, since clearing and cursor
+support is still accelerated, which might be good candidates for further
+deletion projects.
+
+Contact: Daniel Vetter
+
+Level: Intermediate
+
 idr_init_base()
 ---------------
 
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index cef437817b0d..a68253485244 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -1147,11 +1147,13 @@  static void fbcon_init(struct vc_data *vc, int init)
 
 	ops->graphics = 0;
 
-	if ((cap & FBINFO_HWACCEL_COPYAREA) &&
-	    !(cap & FBINFO_HWACCEL_DISABLED))
-		p->scrollmode = SCROLL_MOVE;
-	else /* default to something safe */
-		p->scrollmode = SCROLL_REDRAW;
+	/*
+	 * No more hw acceleration for fbcon.
+	 *
+	 * FIXME: Garbage collect all the now dead code after sufficient time
+	 * has passed.
+	 */
+	p->scrollmode = SCROLL_REDRAW;
 
 	/*
 	 *  ++guenther: console.c:vc_allocate() relies on initializing
@@ -1961,45 +1963,15 @@  static void updatescrollmode(struct fbcon_display *p,
 {
 	struct fbcon_ops *ops = info->fbcon_par;
 	int fh = vc->vc_font.height;
-	int cap = info->flags;
-	u16 t = 0;
-	int ypan = FBCON_SWAP(ops->rotate, info->fix.ypanstep,
-				  info->fix.xpanstep);
-	int ywrap = FBCON_SWAP(ops->rotate, info->fix.ywrapstep, t);
 	int yres = FBCON_SWAP(ops->rotate, info->var.yres, info->var.xres);
 	int vyres = FBCON_SWAP(ops->rotate, info->var.yres_virtual,
 				   info->var.xres_virtual);
-	int good_pan = (cap & FBINFO_HWACCEL_YPAN) &&
-		divides(ypan, vc->vc_font.height) && vyres > yres;
-	int good_wrap = (cap & FBINFO_HWACCEL_YWRAP) &&
-		divides(ywrap, vc->vc_font.height) &&
-		divides(vc->vc_font.height, vyres) &&
-		divides(vc->vc_font.height, yres);
-	int reading_fast = cap & FBINFO_READS_FAST;
-	int fast_copyarea = (cap & FBINFO_HWACCEL_COPYAREA) &&
-		!(cap & FBINFO_HWACCEL_DISABLED);
-	int fast_imageblit = (cap & FBINFO_HWACCEL_IMAGEBLIT) &&
-		!(cap & FBINFO_HWACCEL_DISABLED);
 
 	p->vrows = vyres/fh;
 	if (yres > (fh * (vc->vc_rows + 1)))
 		p->vrows -= (yres - (fh * vc->vc_rows)) / fh;
 	if ((yres % fh) && (vyres % fh < yres % fh))
 		p->vrows--;
-
-	if (good_wrap || good_pan) {
-		if (reading_fast || fast_copyarea)
-			p->scrollmode = good_wrap ?
-				SCROLL_WRAP_MOVE : SCROLL_PAN_MOVE;
-		else
-			p->scrollmode = good_wrap ? SCROLL_REDRAW :
-				SCROLL_PAN_REDRAW;
-	} else {
-		if (reading_fast || (fast_copyarea && !fast_imageblit))
-			p->scrollmode = SCROLL_MOVE;
-		else
-			p->scrollmode = SCROLL_REDRAW;
-	}
 }
 
 #define PITCH(w) (((w) + 7) >> 3)