APM work around for bad bios.

From: Hiroshi Miura (miura@da-cha.org)
Date: Thu Oct 17 2002 - 12:21:55 EST

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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This archive was generated by hypermail 2b29 : Wed Oct 23 2002 - 22:00:36 EST