From: Yifeng Li Date: Mon, 1 Apr 2019 15:46:58 +0000 (+0200) Subject: fbdev: sm712fb: fix white screen of death on reboot, don't set CR3B-CR3F X-Git-Tag: v5.0.19~62 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=4badede3e74b5f59680e903211d4d218578da9a0;p=thirdparty%2Fkernel%2Fstable.git fbdev: sm712fb: fix white screen of death on reboot, don't set CR3B-CR3F commit 8069053880e0ee3a75fd6d7e0a30293265fe3de4 upstream. On a Thinkpad s30 (Pentium III / i440MX, Lynx3DM), rebooting with sm712fb framebuffer driver would cause a white screen of death on the next POST, presumably the proper timings for the LCD panel was not reprogrammed properly by the BIOS. Experiments showed a few CRTC Scratch Registers, including CRT3D, CRT3E and CRT3F may be used internally by BIOS as some flags. CRT3B is a hardware testing register, we shouldn't mess with it. CRT3C has blanking signal and line compare control, which is not needed for this driver. Stop writing to CR3B-CR3F (a.k.a CRT3B-CRT3F) registers. Even if these registers don't have side-effect on other systems, writing to them is also highly questionable. Signed-off-by: Yifeng Li Tested-by: Sudip Mukherjee Cc: Teddy Wang Cc: # v4.4+ Signed-off-by: Bartlomiej Zolnierkiewicz Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/video/fbdev/sm712fb.c b/drivers/video/fbdev/sm712fb.c index 1199895f5c34e..1a3d232c29161 100644 --- a/drivers/video/fbdev/sm712fb.c +++ b/drivers/video/fbdev/sm712fb.c @@ -1173,8 +1173,12 @@ static void sm7xx_set_timing(struct smtcfb_info *sfb) smtc_crtcw(i, vgamode[j].init_cr00_cr18[i]); /* init CRTC register CR30 - CR4D */ - for (i = 0; i < SIZE_CR30_CR4D; i++) + for (i = 0; i < SIZE_CR30_CR4D; i++) { + if ((i + 0x30) >= 0x3B && (i + 0x30) <= 0x3F) + /* side-effect, don't write to CR3B-CR3F */ + continue; smtc_crtcw(i + 0x30, vgamode[j].init_cr30_cr4d[i]); + } /* init CRTC register CR90 - CRA7 */ for (i = 0; i < SIZE_CR90_CRA7; i++)