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From: Hiroshi Miura <miura@da-cha.org>
To: sfr@canb.auug.org.au
Cc: linux-kernel@vger.kernel.org
Subject: APM work around for bad bios.
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Date: Fri, 18 Oct 2002 02:21:55 +0900 (JST)
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Hello,

I use CASIO CASSIOPEIA FIVA 101 and 103. (http://www.da-cha.org/fiva/fiva.html)
this use Cyrix MediaGX and Award BIOS.
This APM BIOS report broken value for dseg_len.
it asumes granularity is 1.

I made a work around for this situation.

  *  if (cseg_len < bios.offset) BIOS report BAD len value.
     -- segment length must be always larger than code offset

  *  if (dseg_len <= 0x40 ) BIOS asumes granularity =1.
     -- 0x40 * 4kB = 64kB, my pc reports 0x40.


diff -urB -x .config -x '*.[oasS]' -x '*.in' -x '*.rej' -x '*.orig' linux-2.5.43-orig/arch/i386/kernel/apm.c linux-2.5.43/arch/i386/kernel/apm.c
--- linux-2.5.43-orig/arch/i386/kernel/apm.c	2002-10-12 13:21:05.000000000 +0900
+++ linux-2.5.43/arch/i386/kernel/apm.c	2002-10-14 21:36:14.000000000 +0900
@@ -1980,6 +2141,14 @@
 				(apm_info.bios.cseg_16_len - 1) & 0xffff);
 			_set_limit((char *)&cpu_gdt_table[i][APM_DS >> 3],
 				(apm_info.bios.dseg_len - 1) & 0xffff);
+		      /* workaround for broken BIOSes */
+	                if (apm_info.bios.cseg_len <= apm_info.bios.offset)
+        	                _set_limit((char *)&cpu_gdt_table[i][APM_CS >> 3], 64 * 1024 -1);
+                       if (apm_info.bios.dseg_len <= 0x40) { /* 0x40 * 4kB == 64kB */
+                        	/* for the BIOS that assumes granularity = 1 */
+                        	cpu_gdt_table[i][APM_DS >> 3].b |= 0x800000;
+                        	printk(KERN_NOTICE "apm: we set the granularity of dseg.\n");
+        	        }
 		}
 #endif
 	}


-- 
Hiroshi Miura  --- http://www.da-cha.org/ 
NTTDATA Corp. Marketing & Business Strategy Planning Dept. --- miurahr@nttdata.co.jp 
Key fingerprint = 9117 9407 5684 FBF1 4063  15B4 401D D077 04AB 8617
-- My hacking life is happy as the day is long

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