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Subject[PATCH v2 1/2] cpu: add generic support for CPU feature based module autoloading
Date
This patch adds support for advertising optional CPU features over udev
using the modalias, and for declaring compatibility with/dependency upon
such a feature in a module.

The mapping between feature numbers and actual features should be provided
by the architecture in a file called <asm/cpufeature.h> which exports the
following functions/macros:
- cpu_feature(FEAT), a preprocessor macro that maps token FEAT to a
numeric index;
- bool cpu_have_feature(n), returning whether this CPU has support for
feature #n;
- MAX_CPU_FEATURES, an upper bound for 'n' in the previous function.

The feature can then be enabled by setting CONFIG_GENERIC_CPU_AUTOPROBE
for the architecture.

For instance, a module that registers its module init function using

module_cpu_feature_match(FEAT_X, module_init_function)

will be probed automatically when the CPU's support for the 'FEAT_X'
feature is advertised over udev, and will only allow the module to be
loaded by hand if the 'FEAT_X' feature is supported.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
---
drivers/base/Kconfig | 8 ++++++
drivers/base/cpu.c | 50 ++++++++++++++++++++++++++++----
include/linux/cpufeature.h | 60 +++++++++++++++++++++++++++++++++++++++
include/linux/mod_devicetable.h | 9 ++++++
scripts/mod/devicetable-offsets.c | 3 ++
scripts/mod/file2alias.c | 10 +++++++
6 files changed, 135 insertions(+), 5 deletions(-)
create mode 100644 include/linux/cpufeature.h

diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
index ec36e77..3f0d373 100644
--- a/drivers/base/Kconfig
+++ b/drivers/base/Kconfig
@@ -185,6 +185,14 @@ config GENERIC_CPU_DEVICES
bool
default n

+config HAVE_CPU_AUTOPROBE
+ def_bool ARCH_HAS_CPU_AUTOPROBE
+
+config GENERIC_CPU_AUTOPROBE
+ bool
+ depends on !ARCH_HAS_CPU_AUTOPROBE
+ select HAVE_CPU_AUTOPROBE
+
config SOC_BUS
bool

diff --git a/drivers/base/cpu.c b/drivers/base/cpu.c
index f48370d..8a38bf8 100644
--- a/drivers/base/cpu.c
+++ b/drivers/base/cpu.c
@@ -15,6 +15,7 @@
#include <linux/percpu.h>
#include <linux/acpi.h>
#include <linux/of.h>
+#include <linux/cpufeature.h>

#include "base.h"

@@ -286,6 +287,45 @@ static void cpu_device_release(struct device *dev)
*/
}

+#ifdef CONFIG_HAVE_CPU_AUTOPROBE
+#ifdef CONFIG_GENERIC_CPU_AUTOPROBE
+static ssize_t print_cpu_modalias(struct device *dev,
+ struct device_attribute *attr,
+ char *buf)
+{
+ ssize_t n;
+ u32 i;
+
+ n = sprintf(buf, "cpu:type:" CPU_FEATURE_TYPEFMT ":feature:",
+ CPU_FEATURE_TYPEVAL);
+
+ for (i = 0; i < MAX_CPU_FEATURES; i++)
+ if (cpu_have_feature(i)) {
+ if (PAGE_SIZE < n + sizeof(",XXXX\n")) {
+ WARN(1, "CPU features overflow page\n");
+ break;
+ }
+ n += sprintf(&buf[n], ",%04X", i);
+ }
+ buf[n++] = '\n';
+ return n;
+}
+#else
+#define print_cpu_modalias arch_print_cpu_modalias
+#endif
+
+static int cpu_uevent(struct device *dev, struct kobj_uevent_env *env)
+{
+ char *buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
+ if (buf) {
+ print_cpu_modalias(NULL, NULL, buf);
+ add_uevent_var(env, "MODALIAS=%s", buf);
+ kfree(buf);
+ }
+ return 0;
+}
+#endif
+
/*
* register_cpu - Setup a sysfs device for a CPU.
* @cpu - cpu->hotpluggable field set to 1 will generate a control file in
@@ -306,8 +346,8 @@ int register_cpu(struct cpu *cpu, int num)
cpu->dev.offline_disabled = !cpu->hotpluggable;
cpu->dev.offline = !cpu_online(num);
cpu->dev.of_node = of_get_cpu_node(num, NULL);
-#ifdef CONFIG_ARCH_HAS_CPU_AUTOPROBE
- cpu->dev.bus->uevent = arch_cpu_uevent;
+#ifdef CONFIG_HAVE_CPU_AUTOPROBE
+ cpu->dev.bus->uevent = cpu_uevent;
#endif
cpu->dev.groups = common_cpu_attr_groups;
if (cpu->hotpluggable)
@@ -330,8 +370,8 @@ struct device *get_cpu_device(unsigned cpu)
}
EXPORT_SYMBOL_GPL(get_cpu_device);

-#ifdef CONFIG_ARCH_HAS_CPU_AUTOPROBE
-static DEVICE_ATTR(modalias, 0444, arch_print_cpu_modalias, NULL);
+#ifdef CONFIG_HAVE_CPU_AUTOPROBE
+static DEVICE_ATTR(modalias, 0444, print_cpu_modalias, NULL);
#endif

static struct attribute *cpu_root_attrs[] = {
@@ -344,7 +384,7 @@ static struct attribute *cpu_root_attrs[] = {
&cpu_attrs[2].attr.attr,
&dev_attr_kernel_max.attr,
&dev_attr_offline.attr,
-#ifdef CONFIG_ARCH_HAS_CPU_AUTOPROBE
+#ifdef CONFIG_HAVE_CPU_AUTOPROBE
&dev_attr_modalias.attr,
#endif
NULL
diff --git a/include/linux/cpufeature.h b/include/linux/cpufeature.h
new file mode 100644
index 0000000..c4d4eb8
--- /dev/null
+++ b/include/linux/cpufeature.h
@@ -0,0 +1,60 @@
+/*
+ * Copyright (C) 2014 Linaro Ltd. <ard.biesheuvel@linaro.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#ifndef __LINUX_CPUFEATURE_H
+#define __LINUX_CPUFEATURE_H
+
+#ifdef CONFIG_GENERIC_CPU_AUTOPROBE
+
+#include <linux/mod_devicetable.h>
+#include <asm/cpufeature.h>
+
+/*
+ * Macros imported from <asm/cpufeature.h>:
+ * - cpu_feature(x) ordinal value of feature called 'x'
+ * - cpu_have_feature(u32 n) whether feature #n is available
+ * - MAX_CPU_FEATURES upper bound for feature ordinal values
+ * Optional:
+ * - CPU_FEATURE_TYPEFMT format string fragment for printing the cpu type
+ * - CPU_FEATURE_TYPEVAL set of values matching the format string above
+ */
+
+#ifndef CPU_FEATURE_TYPEFMT
+#define CPU_FEATURE_TYPEFMT "%s"
+#endif
+
+#ifndef CPU_FEATURE_TYPEVAL
+#define CPU_FEATURE_TYPEVAL ELF_PLATFORM
+#endif
+
+/*
+ * Use module_cpu_feature_match(feature, module_init_function) to
+ * declare that
+ * a) the module shall be probed upon discovery of CPU feature 'feature'
+ * (typically at boot time using udev)
+ * b) the module must not be loaded if CPU feature 'feature' is not present
+ * (not even by manual insmod).
+ *
+ * For a list of legal values for 'feature', please consult the file
+ * 'asm/cpufeature.h' of your favorite architecture.
+ */
+#define module_cpu_feature_match(x, __init) \
+static struct cpu_feature const cpu_feature_match_ ## x[] = \
+ { { .feature = cpu_feature(x) }, { } }; \
+MODULE_DEVICE_TABLE(cpu, cpu_feature_match_ ## x); \
+ \
+static int cpu_feature_match_ ## x ## _init(void) \
+{ \
+ if (!cpu_have_feature(cpu_feature(x))) \
+ return -ENODEV; \
+ return __init(); \
+} \
+module_init(cpu_feature_match_ ## x ## _init)
+
+#endif
+#endif
diff --git a/include/linux/mod_devicetable.h b/include/linux/mod_devicetable.h
index 45e9214..f2ac87c 100644
--- a/include/linux/mod_devicetable.h
+++ b/include/linux/mod_devicetable.h
@@ -564,6 +564,15 @@ struct x86_cpu_id {
#define X86_MODEL_ANY 0
#define X86_FEATURE_ANY 0 /* Same as FPU, you can't test for that */

+/*
+ * Generic table type for matching CPU features.
+ * @feature: the bit number of the feature (0 - 65535)
+ */
+
+struct cpu_feature {
+ __u16 feature;
+};
+
#define IPACK_ANY_FORMAT 0xff
#define IPACK_ANY_ID (~0)
struct ipack_device_id {
diff --git a/scripts/mod/devicetable-offsets.c b/scripts/mod/devicetable-offsets.c
index bb5d115..f282516 100644
--- a/scripts/mod/devicetable-offsets.c
+++ b/scripts/mod/devicetable-offsets.c
@@ -174,6 +174,9 @@ int main(void)
DEVID_FIELD(x86_cpu_id, model);
DEVID_FIELD(x86_cpu_id, vendor);

+ DEVID(cpu_feature);
+ DEVID_FIELD(cpu_feature, feature);
+
DEVID(mei_cl_device_id);
DEVID_FIELD(mei_cl_device_id, name);

diff --git a/scripts/mod/file2alias.c b/scripts/mod/file2alias.c
index 2370863..8a69005 100644
--- a/scripts/mod/file2alias.c
+++ b/scripts/mod/file2alias.c
@@ -1135,6 +1135,16 @@ static int do_x86cpu_entry(const char *filename, void *symval,
}
ADD_TO_DEVTABLE("x86cpu", x86_cpu_id, do_x86cpu_entry);

+/* LOOKS like cpu:type:*:feature:*FEAT* */
+static int do_cpu_entry(const char *filename, void *symval, char *alias)
+{
+ DEF_FIELD(symval, cpu_feature, feature);
+
+ sprintf(alias, "cpu:type:*:feature:*%04X*", feature);
+ return 1;
+}
+ADD_TO_DEVTABLE("cpu", cpu_feature, do_cpu_entry);
+
/* Looks like: mei:S */
static int do_mei_entry(const char *filename, void *symval,
char *alias)
--
1.8.3.2


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