[PATCH v2 2/2] MIPS: cpu-probe: introduce exclusive R3k CPU probe

From: Thomas Bogendoerfer
Date: Thu Oct 08 2020 - 17:33:34 EST

Running a kernel on a R3k of machine definitly will never see one of
the newer CPU cores. And since R3k system usually are low on memory
we could save quite some kbytes:

text data bss dec hex filename
15070 88 32 15190 3b56 arch/mips/kernel/cpu-probe.o
844 4 16 864 360 arch/mips/kernel/cpu-r3k-probe.o

Signed-off-by: Thomas Bogendoerfer <tsbogend@xxxxxxxxxxxxxxxx>
---
arch/mips/kernel/Makefile | 8 +-
arch/mips/kernel/cpu-r3k-probe.c | 171 +++++++++++++++++++++++++++++++++++++++
2 files changed, 178 insertions(+), 1 deletion(-)
create mode 100644 arch/mips/kernel/cpu-r3k-probe.c

diff --git a/arch/mips/kernel/Makefile b/arch/mips/kernel/Makefile
index 026801c21724..2a05b923f579 100644
--- a/arch/mips/kernel/Makefile
+++ b/arch/mips/kernel/Makefile
@@ -5,11 +5,17 @@

extra-y := head.o vmlinux.lds

-obj-y += cmpxchg.o cpu-probe.o branch.o elf.o entry.o genex.o idle.o irq.o \
+obj-y += branch.o cmpxchg.o elf.o entry.o genex.o idle.o irq.o \
process.o prom.o ptrace.o reset.o setup.o signal.o \
syscall.o time.o topology.o traps.o unaligned.o watch.o \
vdso.o cacheinfo.o

+ifdef CONFIG_CPU_R3K_TLB
+obj-y += cpu-r3k-probe.o
+else
+obj-y += cpu-probe.o
+endif
+
ifdef CONFIG_FUNCTION_TRACER
CFLAGS_REMOVE_ftrace.o = -pg
CFLAGS_REMOVE_early_printk.o = -pg
diff --git a/arch/mips/kernel/cpu-r3k-probe.c b/arch/mips/kernel/cpu-r3k-probe.c
new file mode 100644
index 000000000000..abdbbe8c5a43
--- /dev/null
+++ b/arch/mips/kernel/cpu-r3k-probe.c
@@ -0,0 +1,171 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Processor capabilities determination functions.
+ *
+ * Copyright (C) xxxx the Anonymous
+ * Copyright (C) 1994 - 2006 Ralf Baechle
+ * Copyright (C) 2003, 2004 Maciej W. Rozycki
+ * Copyright (C) 2001, 2004, 2011, 2012 MIPS Technologies, Inc.
+ */
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/ptrace.h>
+#include <linux/smp.h>
+#include <linux/stddef.h>
+#include <linux/export.h>
+
+#include <asm/bugs.h>
+#include <asm/cpu.h>
+#include <asm/cpu-features.h>
+#include <asm/cpu-type.h>
+#include <asm/fpu.h>
+#include <asm/mipsregs.h>
+#include <asm/elf.h>
+
+#include "fpu-probe.h"
+
+/* Hardware capabilities */
+unsigned int elf_hwcap __read_mostly;
+EXPORT_SYMBOL_GPL(elf_hwcap);
+
+void __init check_bugs32(void)
+{
+
+}
+
+/*
+ * Probe whether cpu has config register by trying to play with
+ * alternate cache bit and see whether it matters.
+ * It's used by cpu_probe to distinguish between R3000A and R3081.
+ */
+static inline int cpu_has_confreg(void)
+{
+#ifdef CONFIG_CPU_R3000
+ extern unsigned long r3k_cache_size(unsigned long);
+ unsigned long size1, size2;
+ unsigned long cfg = read_c0_conf();
+
+ size1 = r3k_cache_size(ST0_ISC);
+ write_c0_conf(cfg ^ R30XX_CONF_AC);
+ size2 = r3k_cache_size(ST0_ISC);
+ write_c0_conf(cfg);
+ return size1 != size2;
+#else
+ return 0;
+#endif
+}
+
+static inline void set_elf_platform(int cpu, const char *plat)
+{
+ if (cpu == 0)
+ __elf_platform = plat;
+}
+
+const char *__cpu_name[NR_CPUS];
+const char *__elf_platform;
+const char *__elf_base_platform;
+
+void cpu_probe(void)
+{
+ struct cpuinfo_mips *c = &current_cpu_data;
+ unsigned int cpu = smp_processor_id();
+
+ /*
+ * Set a default elf platform, cpu probe may later
+ * overwrite it with a more precise value
+ */
+ set_elf_platform(cpu, "mips");
+
+ c->processor_id = PRID_IMP_UNKNOWN;
+ c->fpu_id = FPIR_IMP_NONE;
+ c->cputype = CPU_UNKNOWN;
+ c->writecombine = _CACHE_UNCACHED;
+
+ c->fpu_csr31 = FPU_CSR_RN;
+ c->fpu_msk31 = FPU_CSR_RSVD | FPU_CSR_ABS2008 | FPU_CSR_NAN2008 |
+ FPU_CSR_CONDX | FPU_CSR_FS;
+
+ c->srsets = 1;
+
+ c->processor_id = read_c0_prid();
+ switch (c->processor_id & (PRID_COMP_MASK | PRID_IMP_MASK)) {
+ case PRID_COMP_LEGACY | PRID_IMP_R2000:
+ c->cputype = CPU_R2000;
+ __cpu_name[cpu] = "R2000";
+ c->options = MIPS_CPU_TLB | MIPS_CPU_3K_CACHE |
+ MIPS_CPU_NOFPUEX;
+ if (__cpu_has_fpu())
+ c->options |= MIPS_CPU_FPU;
+ c->tlbsize = 64;
+ break;
+ case PRID_COMP_LEGACY | PRID_IMP_R3000:
+ if ((c->processor_id & PRID_REV_MASK) == PRID_REV_R3000A) {
+ if (cpu_has_confreg()) {
+ c->cputype = CPU_R3081E;
+ __cpu_name[cpu] = "R3081";
+ } else {
+ c->cputype = CPU_R3000A;
+ __cpu_name[cpu] = "R3000A";
+ }
+ } else {
+ c->cputype = CPU_R3000;
+ __cpu_name[cpu] = "R3000";
+ }
+ c->options = MIPS_CPU_TLB | MIPS_CPU_3K_CACHE |
+ MIPS_CPU_NOFPUEX;
+ if (__cpu_has_fpu())
+ c->options |= MIPS_CPU_FPU;
+ c->tlbsize = 64;
+ break;
+ case PRID_COMP_LEGACY | PRID_IMP_TX39:
+ c->options = MIPS_CPU_TLB | MIPS_CPU_TX39_CACHE;
+
+ if ((c->processor_id & 0xf0) == (PRID_REV_TX3927 & 0xf0)) {
+ c->cputype = CPU_TX3927;
+ __cpu_name[cpu] = "TX3927";
+ c->tlbsize = 64;
+ } else {
+ switch (c->processor_id & PRID_REV_MASK) {
+ case PRID_REV_TX3912:
+ c->cputype = CPU_TX3912;
+ __cpu_name[cpu] = "TX3912";
+ c->tlbsize = 32;
+ break;
+ case PRID_REV_TX3922:
+ c->cputype = CPU_TX3922;
+ __cpu_name[cpu] = "TX3922";
+ c->tlbsize = 64;
+ break;
+ }
+ }
+ break;
+ }
+
+ BUG_ON(!__cpu_name[cpu]);
+ BUG_ON(c->cputype == CPU_UNKNOWN);
+
+ /*
+ * Platform code can force the cpu type to optimize code
+ * generation. In that case be sure the cpu type is correctly
+ * manually setup otherwise it could trigger some nasty bugs.
+ */
+ BUG_ON(current_cpu_type() != c->cputype);
+
+ if (mips_fpu_disabled)
+ c->options &= ~MIPS_CPU_FPU;
+
+ if (c->options & MIPS_CPU_FPU)
+ cpu_set_fpu_opts(c);
+ else
+ cpu_set_nofpu_opts(c);
+}
+
+void cpu_report(void)
+{
+ struct cpuinfo_mips *c = &current_cpu_data;
+
+ pr_info("CPU%d revision is: %08x (%s)\n",
+ smp_processor_id(), c->processor_id, cpu_name_string());
+ if (c->options & MIPS_CPU_FPU)
+ pr_info("FPU revision is: %08x\n", c->fpu_id);
+}
--
2.16.4