drm/bochs: fix blanking

VGA_IS1_RC is the color mode register (VGA_IS1_RM the one for monochrome
mode, note C vs. M at the end).  So when using VGA_IS1_RC make sure the
vga device is actually in color mode and set the corresponding bit in the
misc register.

Reproducible when booting VMs in UEFI mode with some edk2 versions (edk2
fix is on the way too).  Doesn't happen in BIOS mode because in that
case the vgabios already flips the bit.

Fixes: 250e7439 ("drm/bochs: Add screen blanking support")
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: http://patchwork.freedesktop.org/patch/msgid/20220906142957.2763577-1-kraxel@redhat.com

drivers/gpu/drm/tiny/bochs.c

@@ -309,6 +309,8 @@ static void bochs_hw_fini(struct drm_device *dev)
 static void bochs_hw_blank(struct bochs_device *bochs, bool blank)
 {
 	DRM_DEBUG_DRIVER("hw_blank %d\n", blank);
+	/* enable color bit (so VGA_IS1_RC access works) */
+	bochs_vga_writeb(bochs, VGA_MIS_W, VGA_MIS_COLOR);
 	/* discard ar_flip_flop */
 	(void)bochs_vga_readb(bochs, VGA_IS1_RC);
 	/* blank or unblank; we need only update index and set 0x20 */