Re: FAILED: patch "[PATCH] Revert "fbcon: Disable accelerated scrolling"" failed to apply to 5.10-stable tree

On Sat, Feb 5, 2022 at 7:36 PM Helge Deller deller@gmx.de wrote:

• gregkh@linuxfoundation.org gregkh@linuxfoundation.org:

...

The patch below does not apply to the 5.10-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

Hello Greg,

below is a rebased patch which you can use instead and which applies cleanly. The attached patch below is a 100% "git revert 397971e1d891", with added info to the commit message.

After applying the patch below, the other failed patch: "[PATCH] fbcon: Add option to enable legacy hardware acceleration" doesn't fail to apply any longer either.

Please make sure to apply BOTH patches (the one below and the other failed one) or NONE of those two patches.

Ideally, I'd suggest to wait until monday to get an Ack from Daniel for this.

Ack. -Daniel

Thanks, Helge

Replacement patch:

From 19081652e320da7caf1ae5b6a73751cb4ded1e68 Mon Sep 17 00:00:00 2001 From: Helge Deller deller@gmx.de Date: Sat, 5 Feb 2022 19:08:26 +0100 Subject: [PATCH] Revert "fbcon: Disable accelerated scrolling"

This reverts commit 397971e1d891f3af98f96da608ca03ac8cf75e94.

Revert the first (of 2) commits which disabled scrolling acceleration in fbcon/fbdev. It introduced a regression for fbdev-supported graphic cards because of the performance penalty by doing screen scrolling by software instead of using the existing graphic card 2D hardware acceleration.

Console scrolling acceleration was disabled by dropping code which checked at runtime the driver hardware capabilities for the BINFO_HWACCEL_COPYAREA or FBINFO_HWACCEL_FILLRECT flags and if set, it enabled scrollmode SCROLL_MOVE which uses hardware acceleration to move screen contents. After dropping those checks scrollmode was hard-wired to SCROLL_REDRAW instead, which forces all graphic cards to redraw every character at the new screen position when scrolling.

This change effectively disabled all hardware-based scrolling acceleration for ALL drivers, because now all kind of 2D hardware acceleration (bitblt, fillrect) in the drivers isn't used any longer.

The original commit message mentions that only 3 DRM drivers (nouveau, omapdrm and gma500) used hardware acceleration in the past and thus code for checking and using scrolling acceleration is obsolete.

This statement is NOT TRUE, because beside the DRM drivers there are around 35 other fbdev drivers which depend on fbdev/fbcon and still provide hardware acceleration for fbdev/fbcon.

The original commit message also states that syzbot found lots of bugs in fbcon and thus it's "often the solution to just delete code and remove features". This is true, and the bugs - which actually affected all users of fbcon, including DRM - were fixed, or code was dropped like e.g. the support for software scrollback in vgacon (commit 973c096f6a85).

So to further analyze which bugs were found by syzbot, I've looked through all patches in drivers/video which were tagged with syzbot or syzkaller back to year 2005. The vast majority fixed the reported issues on a higher level, e.g. when screen is to be resized, or when font size is to be changed. The few ones which touched driver code fixed a real driver bug, e.g. by adding a check.

But NONE of those patches touched code of either the SCROLL_MOVE or the SCROLL_REDRAW case.

That means, there was no real reason why SCROLL_MOVE had to be ripped-out and just SCROLL_REDRAW had to be used instead. The only reason I can imagine so far was that SCROLL_MOVE wasn't used by DRM and as such it was assumed that it could go away. That argument completely missed the fact that SCROLL_MOVE is still heavily used by fbdev (non-DRM) drivers.

Some people mention that using memcpy() instead of the hardware acceleration is pretty much the same speed. But that's not true, at least not for older graphic cards and machines where we see speed decreases by factor 10 and more and thus this change leads to console responsiveness way worse than before.

That's why the original commit is to be reverted. By reverting we reintroduce hardware-based scrolling acceleration and fix the performance regression for fbdev drivers.

There isn't any impact on DRM when reverting those patches.

Signed-off-by: Helge Deller deller@gmx.de Acked-by: Geert Uytterhoeven geert@linux-m68k.org Acked-by: Sven Schnelle svens@stackframe.org Cc: stable@vger.kernel.org # v5.10+ Signed-off-by: Helge Deller deller@gmx.de Signed-off-by: Daniel Vetter daniel.vetter@ffwll.ch Link: https://patchwork.freedesktop.org/patch/msgid/20220202135531.92183-3-deller@...

diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst index 7272a4bd74dd..28841609aa4f 100644 --- a/Documentation/gpu/todo.rst +++ b/Documentation/gpu/todo.rst @@ -273,24 +273,6 @@ 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 42c72d051158..66eb2dd2166c 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, charcnt = 256;

•   int ret;
  

•   int cap, ret;
  
    if (WARN_ON(info_idx == -1))
        return;
  

@@ -1042,6 +1042,7 @@ 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;
  

@@ -1146,13 +1147,11 @@ static void fbcon_init(struct vc_data *vc, int init)

    ops->graphics = 0;

•   /*
  

•    * No more hw acceleration for fbcon.
  

•    *
  

•    * FIXME: Garbage collect all the now dead code after sufficient time
  

•    * has passed.
  

•    */
  

•   p->scrollmode = SCROLL_REDRAW;
  

•   if ((cap & FBINFO_HWACCEL_COPYAREA) &&
  

•       !(cap & FBINFO_HWACCEL_DISABLED))
  

•           p->scrollmode = SCROLL_MOVE;
  

•   else /* default to something safe */
  

•           p->scrollmode = SCROLL_REDRAW;
  
    /*
     *  ++guenther: console.c:vc_allocate() relies on initializing
  

@@ -1965,15 +1964,45 @@ 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)