From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sasha Levin Date: Sat, 01 Jun 2019 13:25:51 +0000 Subject: [PATCH AUTOSEL 4.4 47/56] fbdev: sm712fb: fix white screen of death on reboot, don't set CR3B-CR3F Message-Id: <20190601132600.27427-47-sashal@kernel.org> List-Id: References: <20190601132600.27427-1-sashal@kernel.org> In-Reply-To: <20190601132600.27427-1-sashal@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Sasha Levin , linux-fbdev@vger.kernel.org, Teddy Wang , Bartlomiej Zolnierkiewicz , dri-devel@lists.freedesktop.org, Yifeng Li , Sudip Mukherjee From: Yifeng Li [ Upstream commit 8069053880e0ee3a75fd6d7e0a30293265fe3de4 ] 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: Sasha Levin --- drivers/video/fbdev/sm712fb.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/video/fbdev/sm712fb.c b/drivers/video/fbdev/sm712fb.c index 3f5840aaa1dd0..5148765f007cf 100644 --- a/drivers/video/fbdev/sm712fb.c +++ b/drivers/video/fbdev/sm712fb.c @@ -1182,8 +1182,12 @@ 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++) -- 2.20.1