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authorDaniel Vetter <daniel.vetter@ffwll.ch>2020-10-29 14:22:29 +0100
committerDaniel Vetter <daniel.vetter@ffwll.ch>2020-11-17 11:00:29 +0100
commit39aead8373b3c20bb5965c024dfb51a94e526151 (patch)
treed82fb5ce2e6a5ed098e526ae36f40eab8455eb5c /drivers/video
parentba236455ee750270f33998df57f982433cea4d8e (diff)
fbcon: Disable accelerated scrolling
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) v3: Remove more unused variables (0day) Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com> 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> Link: https://patchwork.freedesktop.org/patch/msgid/20201029132229.4068359-1-daniel.vetter@ffwll.ch
Diffstat (limited to 'drivers/video')
-rw-r--r--drivers/video/fbdev/core/fbcon.c45
1 files changed, 8 insertions, 37 deletions
diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 06520667fc07..bf61598bf1c3 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -1033,7 +1033,7 @@ static void fbcon_init(struct vc_data *vc, int init)
struct vc_data *svc = *default_mode;
struct fbcon_display *t, *p = &fb_display[vc->vc_num];
int logo = 1, new_rows, new_cols, rows, cols;
- int cap, ret;
+ int ret;
if (WARN_ON(info_idx == -1))
return;
@@ -1042,7 +1042,6 @@ static void fbcon_init(struct vc_data *vc, int init)
con2fb_map[vc->vc_num] = info_idx;
info = registered_fb[con2fb_map[vc->vc_num]];
- cap = info->flags;
if (logo_shown < 0 && console_loglevel <= CONSOLE_LOGLEVEL_QUIET)
logo_shown = FBCON_LOGO_DONTSHOW;
@@ -1144,11 +1143,13 @@ 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
@@ -1957,45 +1958,15 @@ 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)