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Commit 263903a7 authored by Yifeng Li's avatar Yifeng Li Committed by Greg Kroah-Hartman
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fbdev: sm712fb: fix VRAM detection, don't set SR70/71/74/75 



commit dcf9070595e100942c539e229dde4770aaeaa4e9 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: default avatarYifeng Li <tomli@tomli.me>
Tested-by: default avatarSudip Mukherjee <sudipm.mukherjee@gmail.com>
Cc: Teddy Wang <teddy.wang@siliconmotion.com>
Cc: <stable@vger.kernel.org>  # v4.4+
Signed-off-by: default avatarBartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 066009cf

drivers/video/fbdev/sm712fb.c

+3 −1
Original line number Original line Diff line number Diff line
@@ -1145,7 +1145,9 @@ static void sm7xx_set_timing(struct smtcfb_info *sfb) 
		/* init SEQ register SR30 - SR75 */

		/* init SEQ register SR30 - SR75 */

		for (i = 0; i < SIZE_SR30_SR75; i++)

		for (i = 0; i < SIZE_SR30_SR75; i++)

			if ((i + 0x30) != 0x30 && (i + 0x30) != 0x62 &&

			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,

				smtc_seqw(i + 0x30,

					  vgamode[j].init_sr30_sr75[i]);

					  vgamode[j].init_sr30_sr75[i]);