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fbdev: sm712fb: fix VRAM detection, don't set SR70/71/74/75

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commit dcf9070595 upstream.

On a Thinkpad s30 (Pentium III / i440MX, Lynx3DM), the amount of Video
RAM is not detected correctly by the xf86-video-siliconmotion driver.
This is because sm712fb overwrites the GPR71 Scratch Pad Register, which
is set by BIOS on x86 and used to indicate amount of VRAM.

Other Scratch Pad Registers, including GPR70/74/75, don't have the same
side-effect, but overwriting to them is still questionable, as they are
not related to modesetting.

Stop writing to SR70/71/74/75 (a.k.a GPR70/71/74/75).

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>
This commit is contained in:
Yifeng Li
2019-04-01 17:46:58 +02:00
committed by Chris
parent 8e49f38ca2
commit 8835e366a3
1 changed files with 3 additions and 1 deletions
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4
drivers/video/fbdev/sm712fb.c
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@@ -1145,7 +1145,9 @@ static void sm7xx_set_timing(struct smtcfb_info *sfb)
/* init SEQ register SR30 - SR75 */
for (i = 0; i < SIZE_SR30_SR75; i++)
if ((i + 0x30) != 0x30 && (i + 0x30) != 0x62 &&
(i + 0x30) != 0x6a && (i + 0x30) != 0x6b)
(i + 0x30) != 0x6a && (i + 0x30) != 0x6b &&
(i + 0x30) != 0x70 && (i + 0x30) != 0x71 &&
(i + 0x30) != 0x74 && (i + 0x30) != 0x75)
smtc_seqw(i + 0x30,
vgamode[j].init_sr30_sr75[i]);