diff mbox

[RFC,v2,1/2] utils: Add helper to read arm MIDR_EL1 register

Message ID 1471348968-4614-2-git-send-email-vijay.kilari@gmail.com
State Superseded
Headers show

Commit Message

Vijay Kilari Aug. 16, 2016, 12:02 p.m. UTC 
From: Vijaya Kumar K <Vijaya.Kumar@cavium.com>


Add helper API to read MIDR_EL1 registers to fetch
cpu identification information. This helps in
adding errata's and architecture specific features.

This is implemented only for arm architecture.

Signed-off-by: Vijaya Kumar K <Vijaya.Kumar@cavium.com>

---
 include/qemu/aarch64-cpuid.h |  9 +++++
 util/Makefile.objs           |  1 +
 util/aarch64-cpuid.c         | 94 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 104 insertions(+)

-- 
1.9.1

Comments

Peter Maydell Aug. 18, 2016, 2:14 p.m. UTC | #1 
On 18 August 2016 at 15:04, Richard Henderson <rth@twiddle.net> wrote:
> or (2) ifunc


While we're on the subject, can somebody explain to me why we
use ifuncs at all? I couldn't work out why it would be better than
just using a straightforward function pointer -- when I tried single
stepping through things the ifunc approach still seemed to indirect
through some table or other so it wasn't actually resolving to
a direct function call anyway.

thanks
-- PMM
Peter Maydell Aug. 18, 2016, 2:56 p.m. UTC | #2 
On 18 August 2016 at 15:46, Richard Henderson <rth@twiddle.net> wrote:
> On 08/18/2016 07:14 AM, Peter Maydell wrote:

>> While we're on the subject, can somebody explain to me why we

>> use ifuncs at all? I couldn't work out why it would be better than

>> just using a straightforward function pointer -- when I tried single

>> stepping through things the ifunc approach still seemed to indirect

>> through some table or other so it wasn't actually resolving to

>> a direct function call anyway.


> No reason, I suppose.

>

> It's particularly helpful for libraries, where we don't really want the

> overhead of the initialization when it's not used.


Ah, I see.

> But (1) we don't have many of these and (2) we really don't care *that* much

> about startup time.

>

> So a simple function pointer initialized by a constructor has the same

> effect.


That seems like it would be a worthwhile change since
(a) I think it's easier to understand than ifunc magic
(b) it means we don't unnecessarily restrict ourselves to a libc
with ifunc support (musl libc doesn't do ifuncs, for instance)

thanks
-- PMM
diff mbox

Patch

diff --git a/include/qemu/aarch64-cpuid.h b/include/qemu/aarch64-cpuid.h
new file mode 100644
index 0000000..3c11057
--- /dev/null
+++ b/include/qemu/aarch64-cpuid.h
@@ -0,0 +1,9 @@ 
+#ifndef QEMU_AARCH64_CPUID_H
+#define QEMU_AARCH64_CPUID_H
+
+#if defined (__aarch64__)
+uint64_t get_aarch64_cpu_id(void);
+bool is_thunderx_pass2_cpu(void);
+#endif
+
+#endif
diff --git a/util/Makefile.objs b/util/Makefile.objs
index 96cb1e0..aa07bc3 100644
--- a/util/Makefile.objs
+++ b/util/Makefile.objs
@@ -35,3 +35,4 @@  util-obj-y += log.o
 util-obj-y += qdist.o
 util-obj-y += qht.o
 util-obj-y += range.o
+util-obj-y += aarch64-cpuid.o
diff --git a/util/aarch64-cpuid.c b/util/aarch64-cpuid.c
new file mode 100644
index 0000000..42af704
--- /dev/null
+++ b/util/aarch64-cpuid.c
@@ -0,0 +1,94 @@ 
+/*
+ * Dealing with arm cpu identification information.
+ *
+ * Copyright (C) 2016 Cavium, Inc.
+ *
+ * Authors:
+ *  Vijaya Kumar K <Vijaya.Kumar@cavium.com>
+ *
+ * This work is licensed under the terms of the GNU LGPL, version 2.1
+ * or later.  See the COPYING.LIB file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qemu-common.h"
+#include "qemu/cutils.h"
+#include "qemu/aarch64-cpuid.h"
+
+#if defined (__aarch64__)
+#define MIDR_IMPLEMENTER_SHIFT  24
+#define MIDR_IMPLEMENTER_MASK   (0xffULL << MIDR_IMPLEMENTER_SHIFT)
+#define MIDR_ARCHITECTURE_SHIFT 16
+#define MIDR_ARCHITECTURE_MASK  (0xf << MIDR_ARCHITECTURE_SHIFT)
+#define MIDR_PARTNUM_SHIFT      4
+#define MIDR_PARTNUM_MASK       (0xfff << MIDR_PARTNUM_SHIFT)
+
+#define MIDR_CPU_PART(imp, partnum) \
+        (((imp)                 << MIDR_IMPLEMENTER_SHIFT)  | \
+        (0xf                    << MIDR_ARCHITECTURE_SHIFT) | \
+        ((partnum)              << MIDR_PARTNUM_SHIFT))
+
+#define ARM_CPU_IMP_CAVIUM        0x43
+#define CAVIUM_CPU_PART_THUNDERX  0x0A1
+
+#define MIDR_THUNDERX_PASS2  \
+               MIDR_CPU_PART(ARM_CPU_IMP_CAVIUM, CAVIUM_CPU_PART_THUNDERX)
+#define CPU_MODEL_MASK  (MIDR_IMPLEMENTER_MASK | MIDR_ARCHITECTURE_MASK | \
+                         MIDR_PARTNUM_MASK)
+
+static uint64_t qemu_read_aarch64_midr_el1(void)
+{
+#ifdef CONFIG_LINUX
+    const char *file = "/sys/devices/system/cpu/cpu0/regs/identification/midr_el1";
+    char *buf;
+    uint64_t midr = 0;
+
+#define BUF_SIZE 32
+    buf = g_malloc0(BUF_SIZE);
+    if (!buf) {
+        return 0;
+    }
+
+    if (!g_file_get_contents(file, &buf, 0, NULL)) {
+        goto out;
+    }
+
+    if (qemu_strtoull(buf, NULL, 0, &midr) < 0) {
+        goto out;
+    }
+
+out:
+    g_free(buf);
+
+    return midr;
+#else
+    return 0;
+#endif
+}
+
+static bool is_thunderx_cpu;
+static uint64_t aarch64_midr_val;
+uint64_t get_aarch64_cpu_id(void)
+{
+#ifdef CONFIG_LINUX
+    static bool cpu_info_read;
+
+    if (unlikely(!cpu_info_read)) {
+        aarch64_midr_val = qemu_read_aarch64_midr_el1();
+        aarch64_midr_val &= CPU_MODEL_MASK;
+        cpu_info_read = 1;
+        if (aarch64_midr_val == MIDR_THUNDERX_PASS2) {
+            is_thunderx_cpu = 1;
+        }
+    }
+    return aarch64_midr_val;
+#else
+    return 0;
+#endif
+}
+
+bool is_thunderx_pass2_cpu(void)
+{
+   return is_thunderx_cpu;
+}
+#endif