Work around broken BIOSes which report random API subset support bitmaps

when checking for extended INT13 availability for CDROMs

svn path=/trunk/; revision=11741

diff --git a/freeldr/freeldr/arch/i386/pcdisk.c b/freeldr/freeldr/arch/i386/pcdisk.c
index 94be75b..b915141 100644 (file)
--- a/freeldr/freeldr/arch/i386/pcdisk.c
+++ b/freeldr/freeldr/arch/i386/pcdisk.c
@@ -266,11 +266,21 @@ static BOOL PcDiskReadLogicalSectorsCHS(U32 DriveNumber, U64 SectorNumber, U32 S
 
 static BOOL PcDiskInt13ExtensionsSupported(U32 DriveNumber)
 {
+       static U32      LastDriveNumber = 0xffffffff;
+       static BOOL     LastSupported;
        REGS    RegsIn;
        REGS    RegsOut;
 
        DbgPrint((DPRINT_DISK, "PcDiskInt13ExtensionsSupported()\n"));
 
+       if (DriveNumber == LastDriveNumber)
+       {
+               DbgPrint((DPRINT_DISK, "Using cached value %s for drive 0x%x\n", LastSupported ? "TRUE" : "FALSE", DriveNumber));
+               return LastSupported;
+       }
+
+       LastDriveNumber = DriveNumber;
+
        // IBM/MS INT 13 Extensions - INSTALLATION CHECK
        // AH = 41h
        // BX = 55AAh
@@ -305,12 +315,14 @@ static BOOL PcDiskInt13ExtensionsSupported(U32 DriveNumber)
        if (!INT386_SUCCESS(RegsOut))
        {
                // CF set on error (extensions not supported)
+               LastSupported = FALSE;
                return FALSE;
        }
 
        if (RegsOut.w.bx != 0xAA55)
        {
                // BX = AA55h if installed
+               LastSupported = FALSE;
                return FALSE;
        }
 
@@ -323,17 +335,21 @@ static BOOL PcDiskInt13ExtensionsSupported(U32 DriveNumber)
        {
                // CX = API subset support bitmap
                // Bit 0, extended disk access functions (AH=42h-44h,47h,48h) supported
+               LastSupported = FALSE;
                return FALSE;
        }
 #endif
 
-       // Use this relaxed check instead
-       if (RegsOut.w.cx == 0x0000)
+       // Use this relaxed check instead (most BIOSes seem to use 0x9f as CD-Rom)
+       if (RegsOut.w.cx == 0x0000 && DriveNumber != 0x9f)
        {
                // CX = API subset support bitmap
-               return FALSE;
+               printf("Suspicious API subset support bitmap 0x%x on device 0x%x\n", RegsOut.w.cx, DriveNumber);
+               LastSupported = FALSE;
+               return LastSupported;
        }
 
+       LastSupported = TRUE;
        return TRUE;
 }