Re: Weird: 30 sec delay during early boot

[Matt Domsch]

David, Jeff, would you mind trying the patch below on your systems
which exhibit the long delays in the EDD real-mode code?

This does a few things:
1) it uses an int13 fn15 "Get Disk Type" command prior to doing the
fn02 "Read Sectors" command, to try to determine if there is a disk
present or not before reading its signature.

2) A few registers are more fully zeroed out, in case the BIOS cared
about things it shouldn't have.

Crossing my fingers that the delays are gone...
-Matt

-- 
Matt Domsch
Sr. Software Engineer, Lead Engineer
Dell Linux Solutions linux.dell.com & www.dell.com/linux
Linux on Dell mailing lists @ http://lists.us.dell.com

===== arch/i386/boot/edd.S 1.2 vs edited =====
--- 1.2/arch/i386/boot/edd.S	2004-06-29 09:44:48 -05:00
+++ edited/arch/i386/boot/edd.S	2004-07-13 16:48:50 -05:00
@@ -12,13 +12,31 @@
 #include <linux/edd.h>
 
 #if defined(CONFIG_EDD) || defined(CONFIG_EDD_MODULE)
-# Read the first sector of each BIOS disk device and store the 4-byte signature
 edd_mbr_sig_start:
+	xor	%ebx, %ebx
+	xor	%edx, %edx
 	movb	$0, (EDD_MBR_SIG_NR_BUF)	# zero value at EDD_MBR_SIG_NR_BUF
+       	movw	$EDD_MBR_SIG_BUF, %bx		# store buffer ptr in bx
 	movb	$0x80, %dl			# from device 80
-	movw	$EDD_MBR_SIG_BUF, %bx		# store buffer ptr in bx
+
 edd_mbr_sig_read:
-	movl	$0xFFFFFFFF, %eax
+# Do int13 fn15 first, as BIOS should know if a disk is present or not.
+# This avoids long (>30s) delays waiting for the READ_SECTORS to a non-present disk.
+	xor	%eax, %eax
+	xor	%ecx, %ecx
+       	movb	$GETDISKTYPE, %ah		# Function 15
+	pushw	%dx				# which stomps on dx
+	stc					# work around buggy BIOSes
+    	int	$0x13				# make the call
+	sti					# work around buggy BIOSes
+	popw	%dx				# so get back dx
+	jc	edd_mbr_sig_done		# no more BIOS devices
+	cmpb	$HARDDRIVEPRESENT, %ah		# is hard drive present?
+	jne	edd_mbr_sig_done		# no more BIOS devices
+
+# Read the first sector of each BIOS disk device and store the 4-byte signature
+	xor	%ecx, %ecx
+    	movl	$0xFFFFFFFF, %eax
 	movl	%eax, (%bx)			# assume failure
 	pushw	%bx
 	movb	$READ_SECTORS, %ah
===== include/linux/edd.h 1.11 vs edited =====
--- 1.11/include/linux/edd.h	2004-06-29 09:44:48 -05:00
+++ edited/include/linux/edd.h	2004-07-13 16:05:14 -05:00
@@ -49,6 +49,9 @@
 #define EDD_MBR_SIG_MAX 16        /* max number of signatures to store */
 #define EDD_MBR_SIG_NR_BUF 0x1ea  /* addr of number of MBR signtaures at EDD_MBR_SIG_BUF
 				     in boot_params - treat this as 1 byte  */
+#define GETDISKTYPE 0x15          /* int13 AH=0x15 is Get Disk Type command */
+#define HARDDRIVEPRESENT 0x03     /* int13 AH=15 return code in AH */
+
 #ifndef __ASSEMBLY__
 
 #define EDD_EXT_FIXED_DISK_ACCESS           (1 << 0)

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