[Xen-devel] [PATCH RFC 2/3] x86/ACPI: restore VESA mode upon resume from S3

["Jan Beulich" <JBeulich@suse.com>]

In order for "acpi_sleep=s3_mode" to have any effect, we should record
the video mode we switched to during boot. Since right now there's mode
setting code for VESA modes only in the resume case, record the mode
just in that one case.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
---
RFC: On the box that I've been trying to test this on this didn't really
     make a difference (in the random cases where resume works in the
     first place there): The graphics card looks to remain powered off
     even after the Dom0 kernel has resumed. Additionally using
     "acpi_sleep=s3_bios" didn't make a difference either. Furthermore
     it looks like the serial console (connected via PCI card) doesn't
     work (yet) immediately after resume (I suppose it too is powered
     down), and resume hangs altogether with it in use. Hence it's sort
     of difficult to actually debug anything here.
---
I'm wondering actually whether the user having to explicitly request the
mode restoration is a good model: Why would we _not_ want to restore the
mode we've set during boot? In the worst case Dom0 kernel or X will
change the mode another time.

--- a/xen/arch/x86/boot/video.S
+++ b/xen/arch/x86/boot/video.S
@@ -455,14 +455,17 @@ check_vesa:
         cmpb    $0x99, %al
         jnz     _setbad                 # Doh! No linear frame buffer.
 
+        pushw   %bx
         subb    $VIDEO_FIRST_VESA>>8, %bh
         orw     $0x4000, %bx            # Use linear frame buffer
         movw    $0x4f02, %ax            # VESA BIOS mode set call
         int     $0x10
+        popw    %bx
         cmpw    $0x004f, %ax            # AL=4f if implemented
         jnz     _setbad                 # AH=0 if OK
 
         movb    $1, bootsym(graphic_mode)  # flag graphic mode
+        movw    %bx, bootsym(video_mode)
         stc
         ret
 





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