From: Yifeng Li tomli@tomli.me
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 tomli@tomli.me Tested-by: Sudip Mukherjee sudipm.mukherjee@gmail.com Cc: Teddy Wang teddy.wang@siliconmotion.com Cc: stable@vger.kernel.org # v4.4+ Signed-off-by: Bartlomiej Zolnierkiewicz b.zolnierkie@samsung.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- drivers/video/fbdev/sm712fb.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
--- a/drivers/video/fbdev/sm712fb.c +++ b/drivers/video/fbdev/sm712fb.c @@ -1173,8 +1173,12 @@ static void sm7xx_set_timing(struct smtc 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++)