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 <[email protected]> > Reviewed-by: Greg Kroah-Hartman <[email protected]> > Acked-by: Sam Ravnborg <[email protected]> > Cc: Jiri Slaby <[email protected]> > Cc: Bartlomiej Zolnierkiewicz <[email protected]> > Cc: Greg Kroah-Hartman <[email protected]> > Cc: Linus Torvalds <[email protected]> > Cc: Ben Skeggs <[email protected]> > Cc: [email protected] > Cc: Tomi Valkeinen <[email protected]> > Cc: Daniel Vetter <[email protected]> > Cc: Jiri Slaby <[email protected]> > Cc: "Gustavo A. R. Silva" <[email protected]> > Cc: Tetsuo Handa <[email protected]> > Cc: Peilin Ye <[email protected]> > Cc: George Kennedy <[email protected]> > Cc: Nathan Chancellor <[email protected]> > Cc: Peter Rosin <[email protected]> > Signed-off-by: Daniel Vetter <[email protected]> > --- > 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) > -- Thomas Zimmermann Graphics Driver Developer SUSE Software Solutions Germany GmbH Maxfeldstr. 5, 90409 Nürnberg, Germany (HRB 36809, AG Nürnberg) Geschäftsführer: Felix Imendörffer
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