vt: Fix console corruption on driver hand-over.
After 02f0777a "vc_origin" is no longer reset to the screen buffer before calling the con_init() hook of the new console driver. If the old driver wasn't using a fixed scanout buffer (e.g. the case of vgacon) "vc_origin" may be a pointer to a VRAM location, and its contents aren't guaranteed to be preserved after calling con_deinit() on the old driver and con_init() on the new driver, i.e. the subsequent console resize may fill the framebuffer with garbage. It can be reproduced in the transition from vgacon to the nouveau framebuffer driver: in that case the legacy VGA aperture "vc_origin" points to becomes unreadable after fbcon_init(). This patch reverts the mentioned commit. To avoid the problem it intended to fix, stop using "vc_scr_end" in vc_do_resize() to calculate how many rows we have to copy (actually the code looks simpler this way without the help of "vc_scr_end"). Signed-off-by: Francisco Jerez <currojerez@riseup.net> Cc: qiaochong <qiaochong@loongson.cn> Cc: Greg Kroah-Hartman <gregkh@suse.de> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Alan Cox <alan@linux.intel.com> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
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