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    Subject[PATCH 5.0 079/139] fbdev: sm712fb: fix white screen of death on reboot, dont set CR3B-CR3F
    Date
    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++)

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