[PATCH] coresight-stm: adding driver for CoreSight STM component

On 5 February 2015 at 04:27, Paul Bolle [off-list ref] wrote:

On Wed, 2015-02-04 at 15:22 -0700, mathieu.poirier at linaro.org wrote:

quoted

From: Pratik Patel <redacted>

This driver adds support for the STM CoreSight IP block,
allowing any system compoment (HW or SW) to log and
aggregate messages via a single entity.

The STM exposes an application defined number of channels
called stimulus port.  Configuration is done using entries
in sysfs and channels made available to userspace via devfs.

Signed-off-by: Pratik Patel <redacted>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>

This needs "coresight: Adding coresight support for arm64
architecture" (https://lkml.org/lkml/2015/2/3/677 ) in order to get
applied. Perhaps that's obvious to the people working on this.

A few comments follow.

quoted

---
 .../ABI/testing/sysfs-bus-coresight-devices-stm    |   62 ++
 Documentation/trace/coresight.txt                  |   88 +-
 drivers/coresight/Kconfig                          |   10 +
 drivers/coresight/Makefile                         |    1 +
 drivers/coresight/coresight-stm.c                  | 1090 ++++++++++++++++++++
 include/linux/coresight-stm.h                      |   35 +
 include/uapi/linux/coresight-stm.h                 |   23 +
 7 files changed, 1307 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/ABI/testing/sysfs-bus-coresight-devices-stm
 create mode 100644 drivers/coresight/coresight-stm.c
 create mode 100644 include/linux/coresight-stm.h
 create mode 100644 include/uapi/linux/coresight-stm.h

[...]

diff --git a/drivers/coresight/Kconfig b/drivers/coresight/Kconfig
index fc1f1ae7a49d..08806cc7d737 100644
--- a/drivers/coresight/Kconfig
+++ b/drivers/coresight/Kconfig

@@ -58,4 +58,14 @@ config CORESIGHT_SOURCE_ETM3X
        which allows tracing the instructions that a processor is executing
        This is primarily useful for instruction level tracing.  Depending
        the ETM version data tracing may also be available.
+
+config CORESIGHT_STM
+     bool "CoreSight System Trace Macrocell driver"
+     depends on (ARM && !(CPU_32v4 || CPU_32v4T)) || ARM64 || (64BIT && COMPILE_TEST)

I'm _guessing_ that CPU_32v4 and CPU_32v4T are needed for the ldrd and
strd assembler instructions. If that's right a next _guess_ would be
that you also need to mention CPU_32v3 here.

Sorry for the late reply - I've been travelling.

After taking a closer at the Kconfig files I will indeed add CPU_32v3
to the condition.  On the flip side I don't see what the advantage
would be to write  !CPU_32v3 && !CPU_32v4 && !CPU_32v4T as you
suggested.

Furthermore, this file is only sourced by arch/arm/Kconfig.debug and
arch/arm64/Kconfig.debug. So 64BIT should always be equal to ARM64 and
the
     || (64BIT && COMPILE_TEST)

part shouldn't be needed, isn't it?

Correct.

quoted

+     select CORESIGHT_LINKS_AND_SINKS
+     help
+       This driver provides support for hardware assisted software
+       instrumentation based tracing. This is primarily used for
+       logging useful software events or data coming from various entities
+       in the system, possibly running different OSs
 endif
[...]

diff --git a/drivers/coresight/coresight-stm.c b/drivers/coresight/coresight-stm.c
new file mode 100644
index 000000000000..e59b0fe01d87
--- /dev/null
+++ b/drivers/coresight/coresight-stm.c

@@ -0,0 +1,1090 @@

[...]
+#ifndef CONFIG_64BIT
+static inline void __raw_writeq(u64 val, volatile void __iomem *addr)
+{
+     asm volatile("strd %1, %0"
+                  : "+Qo" (*(volatile u64 __force *)addr)
+                  : "r" (val));
+}
+
+static inline u64 __raw_readq(const volatile void __iomem *addr)
+{
+     u64 val;
+
+     asm volatile("ldrd %1, %0"
+                  : "+Qo" (*(volatile u64 __force *)addr),
+                    "=r" (val));
+     return val;
+}
+
+#undef readq_relaxed
+#define readq_relaxed(c) ({ u64 __r = le64_to_cpu((__force __le64) \
+                                     __raw_readq(c)); __r; })

I spotted no users of readq_relaxed. Is it needed?

quoted

+#undef writeq_relaxed
+#define writeq_relaxed(v, c) __raw_writeq((__force u64) cpu_to_le64(v), c)
+#endif
+
[...]

quoted

+static ssize_t entities_show(struct device *dev,
+                          struct device_attribute *attr, char *buf)
+{
+     struct stm_drvdata *drvdata = dev_get_drvdata(dev->parent);
+     ssize_t len;
+
+     len = bitmap_scnprintf(buf, PAGE_SIZE, drvdata->entities,
+                            STM_ENTITY_MAX);
+

bitmap_scnprintf is gone in current linux-next. I changed it to
        len = scnprintf(buf, PAGE_SIZE, "%*pb", STM_ENTITY_MAX,
                        drvdata->entities);

to get this file to compile. (On x86_64, that is, but please don't tell
anybody!)


Paul Bolle