Merge tag 'media/v4.5-2' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab...

[cascardo/linux.git] / 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 3c75210..aa6a317 100644 (file)
--- a/arch/x86/include/asm/bios_ebda.h
+++ b/arch/x86/include/asm/bios_ebda.h
@@ -4,16 +4,40 @@
 #include <asm/io.h>
 
 /*
- * 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 */
 }
 
+/*
+ * 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