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

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Message-ID: <1423135651.27378.32.camel@x220>
Date:	Thu, 05 Feb 2015 12:27:31 +0100
From:	Paul Bolle <pebolle@...cali.nl>
To:	mathieu.poirier@...aro.org
Cc:	corbet@....net, pratikp@...eaurora.org, al.grant@....com,
	liviu.dudau@....com, kaixu.xia@...aro.org,
	jeenu.viswambharan@....com, gregkh@...uxfoundation.org,
	linux-arm-kernel@...ts.infradead.org, linux-api@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH] coresight-stm: adding driver for CoreSight STM component

On Wed, 2015-02-04 at 15:22 -0700, mathieu.poirier@...aro.org wrote:
> From: Pratik Patel <pratikp@...eaurora.org>
> 
> 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 <pratikp@...eaurora.org>
> Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.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.

> ---
>  .../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.

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?

> +	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?

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

> +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

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