[PATCH] Ghost EDD devices in /sys again

[Andrey Borzenkov]

On Friday 05 September 2008, Andrey Borzenkov wrote:
> This is regression but old enough. Apparently I had for whatever reasons
> EDD turned off till recently. This is 2.6.27-rc5 just in case.
> 
> In 2006 I fixed ghost devices due to buggy BIOS:
> 
> http://marc.info/?l=linux-kernel&m=114087765422490&w=2
> 
> Later edd.S has been rewritten in C, and apparently this patch has been
> lost:
> 
> {pts/1}% ls /sys/firmware/edd
> int13_dev80/  int13_dev84/  int13_dev88/  int13_dev8c/
> int13_dev81/  int13_dev85/  int13_dev89/  int13_dev8d/
> int13_dev82/  int13_dev86/  int13_dev8a/  int13_dev8e/
> int13_dev83/  int13_dev87/  int13_dev8b/  int13_dev8f/
> 
> But I have just a single disk. This is the same system BTW.
> 
> Unfortunately I do not speak asm language of C; if somebody could provide
> equivalent fix for current edd.c, I am more than ready to test it.

Was it really that simple?

Subject: [PATCH] Fix ghost devices under /sys/firmware/edd
From: Andrey Borzenkov <arvidjaar@xxxxxxx>

Some BIOSes do not always set CF on error before return from int13.
The patch adds additional check for status being zero (AH == 0).

This was fixed for edd.S in
http://marc.info/?l=linux-kernel&m=114087765422490&w=2, but lost
again when edd.S was rewritten in C.

Signed-off-by: Andrey Borzenkov <arvidjaar@xxxxxxx>

---

 arch/x86/boot/edd.c |    4 +++-
 1 files changed, 3 insertions(+), 1 deletions(-)


diff --git a/arch/x86/boot/edd.c b/arch/x86/boot/edd.c
index d93cbc6..bf4ae6f 100644
--- a/arch/x86/boot/edd.c
+++ b/arch/x86/boot/edd.c
@@ -32,7 +32,9 @@ static int read_mbr(u8 devno, void *buf)
 		     : "+a" (ax), "+c" (cx), "+d" (dx), "+b" (bx)
 		     : : "esi", "edi", "memory");
 
-	return -(u8)ax;		/* 0 or -1 */
+	/* Some BIOSes do not set carry flag on error but still return
+	 * error in AH. The condition below is expected to catch both */
+	return -!!ax;		/* 0 or -1 */
 }
 
 static u32 read_mbr_sig(u8 devno, struct edd_info *ei, u32 *mbrsig)

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