[PATCH 03/21] fbcon: Restore fbcon scrolling acceleration

[Daniel Vetter <daniel.vetter@xxxxxxxx>]

This functionally undoes 39aead8373b3 ("fbcon: Disable accelerated
scrolling"), but behind the FRAMEBUFFER_CONSOLE_LEGACY_ACCELERATION
option.

References: https://lore.kernel.org/dri-devel/feea8303-2b83-fc36-972c-4fc8ad723bde@xxxxxx/
Fixes: 39aead8373b3 ("fbcon: Disable accelerated scrolling")
Cc: Helge Deller <deller@xxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v5.11+
Cc: Claudio Suarez <cssk@xxxxxxxx>
Cc: Dave Airlie <airlied@xxxxxxxxx>
Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Linux Fbdev development list <linux-fbdev@xxxxxxxxxxxxxxx>
Cc: Pavel Machek <pavel@xxxxxx>
Cc: Sam Ravnborg <sam@xxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Javier Martinez Canillas <javierm@xxxxxxxxxx>
Cc: DRI Development <dri-devel@xxxxxxxxxxxxxxxxxxxxx>
Cc: Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>
Cc: Claudio Suarez <cssk@xxxxxxxx>
Cc: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Cc: Thomas Zimmermann <tzimmermann@xxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx>
Cc: Sven Schnelle <svens@xxxxxxxxxxxxxx>
Cc: Gerd Hoffmann <kraxel@xxxxxxxxxx>
Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx>
---
 drivers/video/fbdev/core/fbcon.c | 48 ++++++++++++++++++++++++++++----
 1 file changed, 42 insertions(+), 6 deletions(-)

diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c
index 2ff90061c7f3..39dc18a5de86 100644
--- a/drivers/video/fbdev/core/fbcon.c
+++ b/drivers/video/fbdev/core/fbcon.c
@@ -1125,13 +1125,15 @@ 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.
-	 */
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_ROTATION
+	if ((info->flags & FBINFO_HWACCEL_COPYAREA) &&
+	    !(info->flags & FBINFO_HWACCEL_DISABLED))
+		p->scrollmode = SCROLL_MOVE;
+	else /* default to something safe */
+		p->scrollmode = SCROLL_REDRAW;
+#else
 	p->scrollmode = SCROLL_REDRAW;
+#endif
 
 	/*
 	 *  ++guenther: console.c:vc_allocate() relies on initializing
@@ -1971,15 +1973,49 @@ 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;
+	}
+
+#ifndef CONFIG_FRAMEBUFFER_CONSOLE_ROTATION
+	p->scrollmode = SCROLL_REDRAW;
+#endif
 }
 
 #define PITCH(w) (((w) + 7) >> 3)
-- 
2.33.0