From 57d5f9f808b7650a92f31e9cd3acd3f415a22530 Mon Sep 17 00:00:00 2001 From: Mike Waychison Date: Mon, 14 Mar 2011 23:58:45 -0700 Subject: x86: get_bios_ebda_length() Add a wrapper routine that tells us the length of the EBDA if it is present. This guy also ensures that the returned length doesn't let the EBDA run past the 640KiB mark. Signed-off-by: Mike Waychison Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/bios_ebda.h | 21 +++++++++++++++++++++ 1 file changed, 21 insertions(+) (limited to 'arch/x86/include/asm/bios_ebda.h') diff --git a/arch/x86/include/asm/bios_ebda.h b/arch/x86/include/asm/bios_ebda.h index 3c7521063d3f..5174cf0bf590 100644 --- a/arch/x86/include/asm/bios_ebda.h +++ b/arch/x86/include/asm/bios_ebda.h @@ -14,6 +14,27 @@ static inline unsigned int get_bios_ebda(void) return address; /* 0 means none */ } +/* + * Return the sanitized length of the EBDA in bytes, if it exists. + */ +static inline unsigned int get_bios_ebda_length(void) +{ + unsigned int address; + unsigned int length; + + address = get_bios_ebda(); + if (!address) + return 0; + + /* EBDA length is byte 0 of the EBDA (stored in KiB) */ + length = *(unsigned char *)phys_to_virt(address); + length <<= 10; + + /* Trim the length if it extends beyond 640KiB */ + length = min_t(unsigned int, (640 * 1024) - address, length); + return length; +} + void reserve_ebda_region(void); #ifdef CONFIG_X86_CHECK_BIOS_CORRUPTION -- cgit v1.2.2 From f548ccd47d608e88d432745091e13f927ced83f7 Mon Sep 17 00:00:00 2001 From: Mike Waychison Date: Mon, 14 Mar 2011 23:58:50 -0700 Subject: x86: Better comments for get_bios_ebda() Make the comments a bit clearer for get_bios_ebda so that it actually tells us what it is returning. Signed-off-by: Mike Waychison Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/bios_ebda.h | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) (limited to 'arch/x86/include/asm/bios_ebda.h') diff --git a/arch/x86/include/asm/bios_ebda.h b/arch/x86/include/asm/bios_ebda.h index 5174cf0bf590..aa6a3170ab5a 100644 --- a/arch/x86/include/asm/bios_ebda.h +++ b/arch/x86/include/asm/bios_ebda.h @@ -4,11 +4,14 @@ #include /* - * there is a real-mode segmented pointer pointing to the - * 4K EBDA area at 0x40E. + * Returns physical address of EBDA. Returns 0 if there is no EBDA. */ static inline unsigned int get_bios_ebda(void) { + /* + * There is a real-mode segmented pointer pointing to the + * 4K EBDA area at 0x40E. + */ unsigned int address = *(unsigned short *)phys_to_virt(0x40E); address <<= 4; return address; /* 0 means none */ -- cgit v1.2.2