[alpha] cleanup opDEC workaround

From: Richard Henderson (rth@redhat.com)
Date: Tue Nov 20 2001 - 02:23:55 EST

Would someone with an affected system (Multia or Jensen) try this out?

It removes two global variables, and avoids an extra test once we're
done with startup code.

r~

--- 2.4.15-7/arch/alpha/kernel/traps.c.~2~ Mon Nov 19 23:05:50 2001
+++ 2.4.15-7/arch/alpha/kernel/traps.c Mon Nov 19 23:07:32 2001
@@ -24,31 +24,32 @@
 
 #include "proto.h"
 
-/* data/code implementing a work-around for some SRMs which
- mishandle opDEC faults
-*/
-static int opDEC_testing = 0;
-static int opDEC_fix = 0;
-static unsigned long opDEC_test_pc = 0;
+/* Work-around for some SRMs which mishandle opDEC faults. */
+static int opDEC_fix;
 
 static void
 opDEC_check(void)
 {
- unsigned long test_pc;
+ unsigned long data;
 
- lock_kernel();
- opDEC_testing = 1;
+ /* We temporarily set opDEC_fix so that we skip forward to either
+ the cmpteq (for a broken srm) or the addt (for a working srm).
+ Because of this skip, at the end of the sequence $f0 will be 0
+ for a working srm, and 2.0 for a broken srm. */
 
- __asm__ __volatile__(
- " br %0,1f\n"
- "1: addq %0,8,%0\n"
- " stq %0,%1\n"
- " cvttq/svm $f31,$f31\n"
- : "=&r"(test_pc), "=m"(opDEC_test_pc)
- : );
+ opDEC_fix = 8;
 
- opDEC_testing = 0;
- unlock_kernel();
+ __asm__ __volatile__(
+ "fmov $f31, $f0\n\t"
+ "cvttq/svm $f31, $f31\n\t"
+ "cmpteq $f31, $f31, $f0\n\t"
+ "addt $f31, $f31, $f31\n\t"
+ "stt $f0, %0"
+ : "=m"(data));
+
+ opDEC_fix = data ? 4 : 0;
+ if (data)
+ printk("opDEC fixup enabled.\n");
 }
 
 void
@@ -231,24 +232,22 @@ do_entIF(unsigned long type, unsigned lo
          unsigned long a2, unsigned long a3, unsigned long a4,
          unsigned long a5, struct pt_regs regs)
 {
- if (!opDEC_testing || type != 4) {
- die_if_kernel((type == 1 ? "Kernel Bug" : "Instruction fault"),
- &regs, type, 0);
- }
-
         switch (type) {
- case 0: /* breakpoint */
+ case 0: /* breakpoint */
+ die_if_kernel("Breakpoint fault", &regs, type, 0);
                 if (ptrace_cancel_bpt(current)) {
                         regs.pc -= 4; /* make pc point to former bpt */
                 }
                 send_sig(SIGTRAP, current, 1);
                 return;
 
- case 1: /* bugcheck */
+ case 1: /* bugcheck */
+ die_if_kernel("Kernel Bug", &regs, type, 0);
                 send_sig(SIGTRAP, current, 1);
                 return;
 
- case 2: /* gentrap */
+ case 2: /* gentrap */
+ die_if_kernel("Divide by zero fault", &regs, type, 0);
                 /*
                  * The exception code should be passed on to the signal
                  * handler as the second argument. Linux doesn't do that
@@ -285,27 +284,14 @@ do_entIF(unsigned long type, unsigned lo
                 }
                 break;
 
- case 4: /* opDEC */
+ case 4: /* opDEC */
                 if (implver() == IMPLVER_EV4) {
- /* The some versions of SRM do not handle
- the opDEC properly - they return the PC of the
- opDEC fault, not the instruction after as the
- Alpha architecture requires. Here we fix it up.
- We do this by intentionally causing an opDEC
- fault during the boot sequence and testing if
- we get the correct PC. If not, we set a flag
- to correct it every time through.
- */
- if (opDEC_testing) {
- if (regs.pc == opDEC_test_pc) {
- opDEC_fix = 4;
- regs.pc += 4;
- printk("opDEC fixup enabled.\n");
- }
- return;
- }
+ /* Some versions of SRM do not handle opDEC properly.
+ They return the PC of the opDEC fault, not the
+ instruction after the fault as the architecture
+ requires. Here we fix it up. */
                         regs.pc += opDEC_fix;
-
+
                         /* EV4 does not implement anything except normal
                            rounding. Everything else will come here as
                            an illegal instruction. Emulate them. */
@@ -314,7 +300,7 @@ do_entIF(unsigned long type, unsigned lo
                 }
                 break;
 
- case 3: /* FEN fault */
+ case 3: /* FEN fault */
                 /* Irritating users can call PAL_clrfen to disable the
                    FPU for the process. The kernel will then trap in
                    do_switch_stack and undo_switch_stack when we try
@@ -328,10 +314,12 @@ do_entIF(unsigned long type, unsigned lo
                 __reload_thread(&current->thread);
                 return;
 
- case 5: /* illoc */
- default: /* unexpected instruction-fault type */
- ;
+ case 5: /* illoc */
+ default: /* unexpected instruction-fault type */
+ break;
         }
+
+ die_if_kernel("Instruction fault", &regs, type, 0);
         send_sig(SIGILL, current, 1);
 }
 
@@ -1014,9 +1002,7 @@ trap_init(void)
         wrent(entDbg, 6);
 
         /* Hack for Multia (UDB) and JENSEN: some of their SRMs have
- * a bug in the handling of the opDEC fault. Fix it up if so.
- */
- if (implver() == IMPLVER_EV4) {
+ a bug in the handling of the opDEC fault. Fix it up if so. */
+ if (implver() == IMPLVER_EV4)
                 opDEC_check();
- }
 }
-
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This archive was generated by hypermail 2b29 : Fri Nov 23 2001 - 21:00:22 EST