Messages in this thread Patch in this message | | | Date | Sun, 23 Apr 2006 12:08:27 -0700 | From | "Yum Rayan" <> | Subject | [RFC] VBE DDC bios call stalls boot |
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In my setup I have a monitor connected via a DLink KVM (DKVM 2K). The boot stalls forever during early boot phase until I physically disconnect the KVM from the video port at my CPU box and reconnect it. I was able to trace it to the VBE/DDC call in video.S. The bios call does not seem to return. When I disconnect the video, the bios call returns with failure and boot picks it back from there. When I directly connect my monitor bypassing the KVM, this issue does not happen.
There is a bios call to check if read EDID is supported. My first thought was that before doing read EDID, video.S should first check to see if the hardware supports the read EDID feature. Unfortunately that bios call too ends up in the woods until I physically disconnect/reconnect my CPU video output that feeds into the KVM. I see the same issue with user space programs such as read-edid and xwindows that also attempt to read EDID. They simply stall at the DDC call until I physically disconnect/reconnect my video.
I don't think boot should stall for any reason. Moreover given that user space programs are doing these VBE/DDC calls, I don't see any compelling reason why this code need to exist is such early boot stage. If it absolutely needs to be called in the kernel, at least if invoked sometime later, we could time out this call as a workaround.
Kindly suggest the best approach. The following patch works for me:
Thanks.
--- linux-2.6.15.4.a/arch/i386/boot/video.S 2006-02-09 23:22:48.000000000 -0800 +++ linux-2.6.15.4.b/arch/i386/boot/video.S 2006-04-23 11:19:01.000000000 -0700 @@ -1946,13 +1946,6 @@ store_edid: rep stosl
- movw $0x4f15, %ax # do VBE/DDC - movw $0x01, %bx - movw $0x00, %cx - movw $0x00, %dx - movw $0x140, %di - int $0x10 - popw %di # restore all registers popw %dx popw %cx - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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