On Fri, Aug 19, 2022 at 10:31:30PM -0400, Daniel Dickman wrote:
> The below diff removes detection code for the Cyrix 486DLC and Cyrix 6x86
> CPUs from OpenBSD/i386.
>
> The Cyrix 486DLC is a 486-class CPU which we no longer support.
>
> The 6x86, also known as the M1, does not support CPUID by default. But it
> can be made to support this instruction if bit 7 in CCR4 is enabled. We
> don't do this in the tree today.
>
> The reason to remove support for the 6x86 is because it doesn't support
> the RDTSC instruction which we we use unconditionally. Therefore I don't
> believe Cyrix CPUs older than the 6x86MX (aka the M2) can run
> OpenBSD/i386.
>
> We keep the "cyrix6x86_cpu_setup" function in machdep because those quirks
> would still be needed on the M2.
>
> After this diff, the CPU detection code on i386 would assume that if the
> ID bit is missing from EFLAGS, we're running on an intel 486, while if we
> have the ID bit then we use the CPUID instruction for the detection logic.
>
> We also make the same change to amd64/include/specialreg.h to remove the
> defines for the Cyrix 486DLC. No Cyrix CPU supports amd64, so these
> defines have never made sense there.
>
ok jsg@
>
> Index: i386/i386/locore0.S
> ===================================================================
> RCS file: /cvs/src/sys/arch/i386/i386/locore0.S,v
> retrieving revision 1.7
> diff -u -p -u -r1.7 locore0.S
> --- i386/i386/locore0.S 15 Aug 2022 04:17:50 -0000 1.7
> +++ i386/i386/locore0.S 20 Aug 2022 02:07:30 -0000
> @@ -133,56 +133,6 @@ start: movw $0x1234,0x472 # warm
> boot
> jnz .Ltry586
> .Lis486: movl $CPU_486,RELOC(_C_LABEL(cpu))
>
> - /*
> - * Check Cyrix CPU
> - * Cyrix CPUs do not change the undefined flags following
> - * execution of the divide instruction which divides 5 by 2.
> - *
> - * Note: CPUID is enabled on M2, so it passes another way.
> - */
> - pushfl
> - movl $0x5555, %eax
> - xorl %edx, %edx
> - movl $2, %ecx
> - clc
> - divl %ecx
> - jnc .Ltrycyrix486
> - popfl
> - jmp 2f
> -.Ltrycyrix486:
> - movl $CPU_6x86,RELOC(_C_LABEL(cpu)) # set CPU type
> - /*
> - * Check for Cyrix 486 CPU by seeing if the flags change during a
> - * divide. This is documented in the Cx486SLC/e SMM Programmer's
> - * Guide.
> - */
> - xorl %edx,%edx
> - cmpl %edx,%edx # set flags to known state
> - pushfl
> - popl %ecx # store flags in ecx
> - movl $-1,%eax
> - movl $4,%ebx
> - divl %ebx # do a long division
> - pushfl
> - popl %eax
> - xorl %ecx,%eax # are the flags different?
> - testl $0x8d5,%eax # only check C|PF|AF|Z|N|V
> - jne 2f # yes; must not be Cyrix CPU
> - movl $CPU_486DLC,RELOC(_C_LABEL(cpu)) # set CPU type
> -
> - /* Disable caching of the ISA hole only. */
> - invd
> - movb $CCR0,%al # Configuration Register index (CCR0)
> - outb %al,$0x22
> - inb $0x23,%al
> - orb $(CCR0_NC1|CCR0_BARB),%al
> - movb %al,%ah
> - movb $CCR0,%al
> - outb %al,$0x22
> - movb %ah,%al
> - outb %al,$0x23
> - invd
> -
> jmp 2f
>
> .Ltry586: /* Use the `cpuid' instruction. */
> Index: i386/i386/machdep.c
> ===================================================================
> RCS file: /cvs/src/sys/arch/i386/i386/machdep.c,v
> retrieving revision 1.653
> diff -u -p -u -r1.653 machdep.c
> --- i386/i386/machdep.c 18 Aug 2022 13:05:43 -0000 1.653
> +++ i386/i386/machdep.c 20 Aug 2022 02:07:30 -0000
> @@ -498,14 +498,8 @@ char cpu_model[120];
> * We deal with the rest in a different way.
> */
> const struct cpu_nocpuid_nameclass i386_nocpuid_cpus[] = {
> - { CPUVENDOR_INTEL, "Intel", "486SX", CPUCLASS_486,
> - NULL}, /* CPU_486SX */
> { CPUVENDOR_INTEL, "Intel", "486DX", CPUCLASS_486,
> NULL}, /* CPU_486 */
> - { CPUVENDOR_CYRIX, "Cyrix", "486DLC", CPUCLASS_486,
> - NULL}, /* CPU_486DLC */
> - { CPUVENDOR_CYRIX, "Cyrix", "6x86", CPUCLASS_486,
> - cyrix6x86_cpu_setup}, /* CPU_6x86 */
> };
>
> const char *classnames[] = {
> @@ -2075,9 +2069,6 @@ identifycpu(struct cpu_info *ci)
> cpu_class = class;
>
> ci->cpu_class = class;
> -
> - if (cpu == CPU_486DLC)
> - printf("WARNING: CYRIX 486DLC CACHE UNCHANGED.\n");
>
> /*
> * Enable ring 0 write protection.
> Index: i386/include/cputypes.h
> ===================================================================
> RCS file: /cvs/src/sys/arch/i386/include/cputypes.h,v
> retrieving revision 1.13
> diff -u -p -u -r1.13 cputypes.h
> --- i386/include/cputypes.h 15 Aug 2022 04:17:51 -0000 1.13
> +++ i386/include/cputypes.h 20 Aug 2022 02:07:30 -0000
> @@ -37,19 +37,10 @@
> #define CPUCLASS_686 3
>
> /*
> - * Kinds of Processor. Only the first 7 are used, as they are processors
> - * that might not have a cpuid instruction.
> + * Kind of Processor.
> */
>
> -#define CPU_486SX 2 /* Intel 80486SX */
> -#define CPU_486 3 /* Intel 80486DX */
> -#define CPU_486DLC 4 /* Cyrix 486DLC */
> -#define CPU_6x86 5 /* Cyrix/IBM 6x86 */
> -#define CPU_586 7 /* Intel P.....m (I hate lawyers; it's
> TM) */
> -#define CPU_AM586 8 /* AMD Am486 and Am5x86 */
> -#define CPU_K5 9 /* AMD K5 */
> -#define CPU_K6 10 /* AMD K6 */
> -#define CPU_686 11 /* Intel P.....m Pro */
> +#define CPU_486 0 /* Intel 80486DX */
>
> /*
> * CPU vendors
> Index: i386/include/specialreg.h
> ===================================================================
> RCS file: /cvs/src/sys/arch/i386/include/specialreg.h,v
> retrieving revision 1.79
> diff -u -p -u -r1.79 specialreg.h
> --- i386/include/specialreg.h 21 Feb 2022 10:06:35 -0000 1.79
> +++ i386/include/specialreg.h 20 Aug 2022 02:07:30 -0000
> @@ -52,23 +52,6 @@
> #define CR0_CD 0x40000000 /* Cache Disable */
>
> /*
> - * Cyrix 486 DLC special registers, accessible as IO ports.
> - */
> -#define CCR0 0xc0 /* configuration control register 0 */
> -#define CCR0_NC0 0x01 /* first 64K of each 1M memory region is
> non-cacheable */
> -#define CCR0_NC1 0x02 /* 640K-1M region is non-cacheable */
> -#define CCR0_A20M 0x04 /* enables A20M# input pin */
> -#define CCR0_KEN 0x08 /* enables KEN# input pin */
> -#define CCR0_FLUSH 0x10 /* enables FLUSH# input pin */
> -#define CCR0_BARB 0x20 /* flushes internal cache when entering hold
> state */
> -#define CCR0_CO 0x40 /* cache org: 1=direct mapped, 0=2x set
> assoc */
> -#define CCR0_SUSPEND 0x80 /* enables SUSP# and SUSPA# pins */
> -
> -#define CCR1 0xc1 /* configuration control register 1 */
> -#define CCR1_RPL 0x01 /* enables RPLSET and RPLVAL# pins */
> -/* the remaining 7 bits of this register are reserved */
> -
> -/*
> * bits in CR3
> */
> #define CR3_PWT (1ULL << 3)
> Index: amd64/include/specialreg.h
> ===================================================================
> RCS file: /cvs/src/sys/arch/amd64/include/specialreg.h,v
> retrieving revision 1.92
> diff -u -p -u -r1.92 specialreg.h
> --- amd64/include/specialreg.h 26 Apr 2022 08:35:30 -0000 1.92
> +++ amd64/include/specialreg.h 20 Aug 2022 02:07:30 -0000
> @@ -53,23 +53,6 @@
> #define CR0_CD 0x40000000 /* Cache Disable */
>
> /*
> - * Cyrix 486 DLC special registers, accessible as IO ports.
> - */
> -#define CCR0 0xc0 /* configuration control register 0 */
> -#define CCR0_NC0 0x01 /* first 64K of each 1M memory region is
> non-cacheable */
> -#define CCR0_NC1 0x02 /* 640K-1M region is non-cacheable */
> -#define CCR0_A20M 0x04 /* enables A20M# input pin */
> -#define CCR0_KEN 0x08 /* enables KEN# input pin */
> -#define CCR0_FLUSH 0x10 /* enables FLUSH# input pin */
> -#define CCR0_BARB 0x20 /* flushes internal cache when entering hold
> state */
> -#define CCR0_CO 0x40 /* cache org: 1=direct mapped, 0=2x set
> assoc */
> -#define CCR0_SUSPEND 0x80 /* enables SUSP# and SUSPA# pins */
> -
> -#define CCR1 0xc1 /* configuration control register 1 */
> -#define CCR1_RPL 0x01 /* enables RPLSET and RPLVAL# pins */
> -/* the remaining 7 bits of this register are reserved */
> -
> -/*
> * bits in CR3
> */
> #define CR3_PCID 0xfffULL
>
>
