diff mbox series

[v2] stm: class: Add MIPI OST protocol support

Message ID 20230419141328.37472-1-quic_jinlmao@quicinc.com (mailing list archive)
State New, archived
Headers show
Series [v2] stm: class: Add MIPI OST protocol support | expand

Commit Message

Mao Jinlong April 19, 2023, 2:13 p.m. UTC
Add MIPI OST(Open System Trace) protocol support for stm to format
the traces. OST over STP packet consists of Header/Payload/End. In
header, there will be STARTSIMPLE/VERSION/ENTITY/PROTOCOL. STARTSIMPLE
is used to signal the beginning of a simplified OST base protocol
packet.The Entity ID field is a one byte unsigned number that identifies
the source. FLAG packet is used for END token.

Signed-off-by: Tingwei Zhang <quic_tingweiz@quicinc.com>
Signed-off-by: Yuanfang Zhang <quic_yuanfang@quicinc.com>
Signed-off-by: Mao Jinlong <quic_jinlmao@quicinc.com>
---
 .../ABI/testing/configfs-stp-policy-p_ost     |  13 ++
 Documentation/trace/p_ost.rst                 |  40 ++++
 drivers/hwtracing/stm/Kconfig                 |  14 ++
 drivers/hwtracing/stm/Makefile                |   2 +
 drivers/hwtracing/stm/p_ost.c                 | 213 ++++++++++++++++++
 5 files changed, 282 insertions(+)
 create mode 100644 Documentation/ABI/testing/configfs-stp-policy-p_ost
 create mode 100644 Documentation/trace/p_ost.rst
 create mode 100644 drivers/hwtracing/stm/p_ost.c

Comments

kernel test robot April 19, 2023, 6:25 p.m. UTC | #1
Hi Mao,

kernel test robot noticed the following build errors:

[auto build test ERROR on atorgue-stm32/stm32-next]
[also build test ERROR on linus/master v6.3-rc7 next-20230418]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Mao-Jinlong/stm-class-Add-MIPI-OST-protocol-support/20230419-221653
base:   https://git.kernel.org/pub/scm/linux/kernel/git/atorgue/stm32.git stm32-next
patch link:    https://lore.kernel.org/r/20230419141328.37472-1-quic_jinlmao%40quicinc.com
patch subject: [PATCH v2] stm: class: Add MIPI OST protocol support
config: sparc-allyesconfig (https://download.01.org/0day-ci/archive/20230420/202304200216.kvZgZcao-lkp@intel.com/config)
compiler: sparc64-linux-gcc (GCC) 12.1.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # https://github.com/intel-lab-lkp/linux/commit/54db7d137859caf5a14de2b166d80913b0c80218
        git remote add linux-review https://github.com/intel-lab-lkp/linux
        git fetch --no-tags linux-review Mao-Jinlong/stm-class-Add-MIPI-OST-protocol-support/20230419-221653
        git checkout 54db7d137859caf5a14de2b166d80913b0c80218
        # save the config file
        mkdir build_dir && cp config build_dir/.config
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=sparc olddefconfig
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-12.1.0 make.cross W=1 O=build_dir ARCH=sparc SHELL=/bin/bash drivers/

If you fix the issue, kindly add following tag where applicable
| Reported-by: kernel test robot <lkp@intel.com>
| Link: https://lore.kernel.org/oe-kbuild-all/202304200216.kvZgZcao-lkp@intel.com/

All error/warnings (new ones prefixed by >>):

   drivers/hwtracing/stm/p_ost.c: In function 'ost_write':
>> drivers/hwtracing/stm/p_ost.c:174:46: error: implicit declaration of function 'get_current'; did you mean 'get_cred'? [-Werror=implicit-function-declaration]
     174 |         *(u64 *)(trc_hdr + 8) = task_tgid_nr(get_current());
         |                                              ^~~~~~~~~~~
         |                                              get_cred
>> drivers/hwtracing/stm/p_ost.c:174:46: warning: passing argument 1 of 'task_tgid_nr' makes pointer from integer without a cast [-Wint-conversion]
     174 |         *(u64 *)(trc_hdr + 8) = task_tgid_nr(get_current());
         |                                              ^~~~~~~~~~~~~
         |                                              |
         |                                              int
   In file included from include/linux/sched/mm.h:7,
                    from include/linux/xarray.h:19,
                    from include/linux/radix-tree.h:21,
                    from include/linux/idr.h:15,
                    from include/linux/kernfs.h:12,
                    from include/linux/sysfs.h:16,
                    from include/linux/kobject.h:20,
                    from include/linux/module.h:21,
                    from drivers/hwtracing/stm/p_ost.c:9:
   include/linux/sched.h:1582:54: note: expected 'struct task_struct *' but argument is of type 'int'
    1582 | static inline pid_t task_tgid_nr(struct task_struct *tsk)
         |                                  ~~~~~~~~~~~~~~~~~~~~^~~
   cc1: some warnings being treated as errors


vim +174 drivers/hwtracing/stm/p_ost.c

   131	
   132	static ssize_t notrace ost_write(struct stm_data *data,
   133			struct stm_output *output, unsigned int chan,
   134			const char *buf, size_t count)
   135	{
   136		unsigned int c = output->channel + chan;
   137		unsigned int m = output->master;
   138		const unsigned char nil = 0;
   139		u32 header = DATA_HEADER;
   140		u8 trc_hdr[16];
   141		ssize_t sz;
   142	
   143		struct ost_output *op = output->pdrv_private;
   144	
   145		/*
   146		 * Identify the source by entity type.
   147		 * If entity type is not set, return error value.
   148		 */
   149		if (op->node.entity_type == OST_ENTITY_TYPE_FTRACE) {
   150			header |= OST_ENTITY_FTRACE;
   151		} else if (op->node.entity_type == OST_ENTITY_TYPE_CONSOLE) {
   152			header |= OST_ENTITY_CONSOLE;
   153		} else {
   154			pr_debug("p_ost: Entity must be set for trace data.");
   155			return -EINVAL;
   156		}
   157	
   158		/*
   159		 * STP framing rules for OST frames:
   160		 *   * the first packet of the OST frame is marked;
   161		 *   * the last packet is a FLAG with timestamped tag.
   162		 */
   163		/* Message layout: HEADER / DATA / TAIL */
   164		/* HEADER */
   165		sz = data->packet(data, m, c, STP_PACKET_DATA, STP_PACKET_MARKED,
   166				  4, (u8 *)&header);
   167		if (sz <= 0)
   168			return sz;
   169	
   170		/* DATA */
   171		*(u16 *)(trc_hdr) = STM_MAKE_VERSION(0, 4);
   172		*(u16 *)(trc_hdr + 2) = STM_HEADER_MAGIC;
   173		*(u32 *)(trc_hdr + 4) = raw_smp_processor_id();
 > 174		*(u64 *)(trc_hdr + 8) = task_tgid_nr(get_current());
   175		sz = stm_data_write(data, m, c, false, trc_hdr, sizeof(trc_hdr));
   176		if (sz <= 0)
   177			return sz;
   178	
   179		sz = stm_data_write(data, m, c, false, buf, count);
   180	
   181		/* TAIL */
   182		if (sz > 0)
   183			data->packet(data, m, c, STP_PACKET_FLAG,
   184				STP_PACKET_TIMESTAMPED, 0, &nil);
   185	
   186		return sz;
   187	}
   188
Alexander Shishkin April 20, 2023, 10:02 a.m. UTC | #2
Mao Jinlong <quic_jinlmao@quicinc.com> writes:

> Add MIPI OST(Open System Trace) protocol support for stm to format
> the traces. OST over STP packet consists of Header/Payload/End. In
> header, there will be STARTSIMPLE/VERSION/ENTITY/PROTOCOL. STARTSIMPLE
> is used to signal the beginning of a simplified OST base protocol
> packet.The Entity ID field is a one byte unsigned number that identifies
> the source. FLAG packet is used for END token.

We'd need a better explanation of what OST is, maybe a link to the spec
if one exists.

Another thing that this patch does is adding source identification,
which needs to be described better.

[...]

> +CONFIG_STM_PROTO_OST is for p_ost driver enablement. Once this config
> +is enabled, you can select the p_ost protocol by command below:
> +
> +# mkdir /sys/kernel/config/stp-policy/stm0:p_ost.policy
> +
> +The policy name format is extended like this:
> +    <device_name>:<protocol_name>.<policy_name>
> +
> +With coresight-stm device, it will be look like "stm0:p_ost.policy".

The part about protocol selection should probably be in stm.rst
instead.

> +You can check if the protocol is set successfully by:
> +# cat /sys/kernel/config/stp-policy/stm0:p_ost.policy/protocol
> +p_ost

A successful mkdir is technically enough.

> +With MIPI OST protocol driver, the attributes for each protocol node is:
> +# mkdir /sys/kernel/config/stp-policy/stm0:p_ost.policy/default
> +# ls /sys/kernel/config/stp-policy/stm0:p_ost.policy/default
> +channels  entity    masters

Where's "entity_available"?

> +The entity here is the set the entity that p_ost supports. Currently
> +p_ost supports ftrace and console entity.
> +
> +Get current available entity that p_ost supports:
> +# cat /sys/kernel/config/stp-policy/stm0:p_ost.policy/default/entity_available
> +ftrace console
> +
> +Set entity:
> +# echo 'ftrace' > /sys/kernel/config/stp-policy/stm0:p_ost.policy/default/entity

This is not a very good example, as it will flag everything that goes
through STM as "ftrace", which is probably not what anybody wants.

The bigger question is, why do we need to set the source type (for
which "entity" is not a very good name, btw) in the configfs when
corresponding stm source drivers already carry this information.
There should be a way to propagate the source type from stm source
driver to the protocol driver without relying on the user to set it
correctly.

> +See Documentation/ABI/testing/configfs-stp-policy-p_ost for more details.
> diff --git a/drivers/hwtracing/stm/Kconfig b/drivers/hwtracing/stm/Kconfig
> index eda6b11d40a1..daa4aa09f64d 100644
> --- a/drivers/hwtracing/stm/Kconfig
> +++ b/drivers/hwtracing/stm/Kconfig
> @@ -40,6 +40,20 @@ config STM_PROTO_SYS_T
>  
>  	  If you don't know what this is, say N.
>  
> +config STM_PROTO_OST
> +	tristate "MIPI OST STM framing protocol driver"
> +	default CONFIG_STM
> +	help
> +	  This is an implementation of MIPI OST protocol to be used
> +	  over the STP transport. In addition to the data payload, it
> +	  also carries additional metadata for entity, better
> +	  means of trace source identification, etc.

What does "entity" mean here?

[...]

> +#define OST_TOKEN_STARTSIMPLE		(0x10)
> +#define OST_VERSION_MIPI1		(0x10 << 8)

Either write them as bits (BIT(12)) or as a hex value (0x1000).

> +/* entity id to identify the source*/
> +#define OST_ENTITY_FTRACE		(0x01 << 16)
> +#define OST_ENTITY_CONSOLE		(0x02 << 16)
> +
> +#define OST_CONTROL_PROTOCOL		(0x0 << 24)

Zero, really? At this point I'm wondering if this code has even been
tested.

[...]

> +static ssize_t
> +ost_t_policy_entity_store(struct config_item *item, const char *page,
> +			size_t count)
> +{
> +	struct mutex *mutexp = &item->ci_group->cg_subsys->su_mutex;
> +	struct ost_policy_node *pn = to_pdrv_policy_node(item);
> +	char str[10] = "";
> +
> +	mutex_lock(mutexp);
> +	if (sscanf(page, "%s", str) != 1)
> +		return -EINVAL;
> +	mutex_unlock(mutexp);

You forgot to release the mutex in the error path.
Also, why do you need a mutex around sscanf() in the first place?
Also, the sscanf() can overrun str.

> +	if (!strcmp(str, str_ost_entity_type[OST_ENTITY_TYPE_FTRACE]))
> +		pn->entity_type = OST_ENTITY_TYPE_FTRACE;
> +	else if (!strcmp(str, str_ost_entity_type[OST_ENTITY_TYPE_CONSOLE]))
> +		pn->entity_type = OST_ENTITY_TYPE_CONSOLE;

Why can't you strcmp() on the page directly?
Also, this is where you do want to hold the mutex.
Also, what if there are more source types?

> +	else
> +		return -EINVAL;
> +	return count;
> +}
> +CONFIGFS_ATTR(ost_t_policy_, entity);
> +
> +static ssize_t ost_t_policy_entity_available_show(struct config_item *item,
> +				char *page)
> +{
> +	return scnprintf(page, PAGE_SIZE, "%s\n", "ftrace console");

Don't hardcode these.

> +}
> +CONFIGFS_ATTR_RO(ost_t_policy_, entity_available);
> +
> +static struct configfs_attribute *ost_t_policy_attrs[] = {
> +	&ost_t_policy_attr_entity,
> +	&ost_t_policy_attr_entity_available,
> +	NULL,
> +};
> +
> +static ssize_t notrace ost_write(struct stm_data *data,
> +		struct stm_output *output, unsigned int chan,
> +		const char *buf, size_t count)
> +{
> +	unsigned int c = output->channel + chan;
> +	unsigned int m = output->master;
> +	const unsigned char nil = 0;
> +	u32 header = DATA_HEADER;
> +	u8 trc_hdr[16];
> +	ssize_t sz;
> +
> +	struct ost_output *op = output->pdrv_private;

As said above, the stm source driver that calls here already knows its
own source type, there's no need to store it separately.

> +
> +	/*
> +	 * Identify the source by entity type.
> +	 * If entity type is not set, return error value.
> +	 */
> +	if (op->node.entity_type == OST_ENTITY_TYPE_FTRACE) {
> +		header |= OST_ENTITY_FTRACE;
> +	} else if (op->node.entity_type == OST_ENTITY_TYPE_CONSOLE) {
> +		header |= OST_ENTITY_CONSOLE;
> +	} else {
> +		pr_debug("p_ost: Entity must be set for trace data.");

You forgot a newline.
Also, this message seems to be quite useless: it's either a nop or a
dmesg storm. In general, it's a bad idea to printk() in the write
callback.

> +		return -EINVAL;
> +	}
> +
> +	/*
> +	 * STP framing rules for OST frames:
> +	 *   * the first packet of the OST frame is marked;
> +	 *   * the last packet is a FLAG with timestamped tag.
> +	 */
> +	/* Message layout: HEADER / DATA / TAIL */
> +	/* HEADER */
> +	sz = data->packet(data, m, c, STP_PACKET_DATA, STP_PACKET_MARKED,
> +			  4, (u8 *)&header);
> +	if (sz <= 0)
> +		return sz;
> +
> +	/* DATA */
> +	*(u16 *)(trc_hdr) = STM_MAKE_VERSION(0, 4);
> +	*(u16 *)(trc_hdr + 2) = STM_HEADER_MAGIC;
> +	*(u32 *)(trc_hdr + 4) = raw_smp_processor_id();
> +	*(u64 *)(trc_hdr + 8) = task_tgid_nr(get_current());

What's the value in exporting PIDs when there are PID namespaces? How is
this useful? Also, neither console nor ftrace are required to come in a
task context.

I already asked in the previous version, why is trc_hdr not a struct?

There also used to be a timestamp field in trc_hdr, what happened to it?

Regards,
--
Alex
diff mbox series

Patch

diff --git a/Documentation/ABI/testing/configfs-stp-policy-p_ost b/Documentation/ABI/testing/configfs-stp-policy-p_ost
new file mode 100644
index 000000000000..7ad11ae21760
--- /dev/null
+++ b/Documentation/ABI/testing/configfs-stp-policy-p_ost
@@ -0,0 +1,13 @@ 
+What:		/config/stp-policy/<device>:p_ost.<policy>/<node>/entity_available
+Date:		April 2023
+KernelVersion:	6.3
+Description:
+		Show entity that p_ost supports, RO.
+
+What:		/config/stp-policy/<device>:p_ost.<policy>/<node>/entity
+Date:		April 2023
+KernelVersion:	6.3
+Description:
+		Set the entity which is to identify the source, RW.
+		The available entity can be gotten by reading entity_available.
+
diff --git a/Documentation/trace/p_ost.rst b/Documentation/trace/p_ost.rst
new file mode 100644
index 000000000000..8d7afa341b9e
--- /dev/null
+++ b/Documentation/trace/p_ost.rst
@@ -0,0 +1,40 @@ 
+.. SPDX-License-Identifier: GPL-2.0
+
+===================
+MIPI OST over STP
+===================
+
+The OST(Open System Trace) driver is used with STM class devices to
+generate standardized trace stream. Trace sources can be identified
+by different entity ids.
+
+CONFIG_STM_PROTO_OST is for p_ost driver enablement. Once this config
+is enabled, you can select the p_ost protocol by command below:
+
+# mkdir /sys/kernel/config/stp-policy/stm0:p_ost.policy
+
+The policy name format is extended like this:
+    <device_name>:<protocol_name>.<policy_name>
+
+With coresight-stm device, it will be look like "stm0:p_ost.policy".
+
+You can check if the protocol is set successfully by:
+# cat /sys/kernel/config/stp-policy/stm0:p_ost.policy/protocol
+p_ost
+
+With MIPI OST protocol driver, the attributes for each protocol node is:
+# mkdir /sys/kernel/config/stp-policy/stm0:p_ost.policy/default
+# ls /sys/kernel/config/stp-policy/stm0:p_ost.policy/default
+channels  entity    masters
+
+The entity here is the set the entity that p_ost supports. Currently
+p_ost supports ftrace and console entity.
+
+Get current available entity that p_ost supports:
+# cat /sys/kernel/config/stp-policy/stm0:p_ost.policy/default/entity_available
+ftrace console
+
+Set entity:
+# echo 'ftrace' > /sys/kernel/config/stp-policy/stm0:p_ost.policy/default/entity
+
+See Documentation/ABI/testing/configfs-stp-policy-p_ost for more details.
diff --git a/drivers/hwtracing/stm/Kconfig b/drivers/hwtracing/stm/Kconfig
index eda6b11d40a1..daa4aa09f64d 100644
--- a/drivers/hwtracing/stm/Kconfig
+++ b/drivers/hwtracing/stm/Kconfig
@@ -40,6 +40,20 @@  config STM_PROTO_SYS_T
 
 	  If you don't know what this is, say N.
 
+config STM_PROTO_OST
+	tristate "MIPI OST STM framing protocol driver"
+	default CONFIG_STM
+	help
+	  This is an implementation of MIPI OST protocol to be used
+	  over the STP transport. In addition to the data payload, it
+	  also carries additional metadata for entity, better
+	  means of trace source identification, etc.
+
+	  The receiving side must be able to decode this protocol in
+	  addition to the MIPI STP, in order to extract the data.
+
+	  If you don't know what this is, say N.
+
 config STM_DUMMY
 	tristate "Dummy STM driver"
 	help
diff --git a/drivers/hwtracing/stm/Makefile b/drivers/hwtracing/stm/Makefile
index 1692fcd29277..715fc721891e 100644
--- a/drivers/hwtracing/stm/Makefile
+++ b/drivers/hwtracing/stm/Makefile
@@ -5,9 +5,11 @@  stm_core-y		:= core.o policy.o
 
 obj-$(CONFIG_STM_PROTO_BASIC) += stm_p_basic.o
 obj-$(CONFIG_STM_PROTO_SYS_T) += stm_p_sys-t.o
+obj-$(CONFIG_STM_PROTO_OST) += stm_p_ost.o
 
 stm_p_basic-y		:= p_basic.o
 stm_p_sys-t-y		:= p_sys-t.o
+stm_p_ost-y		:= p_ost.o
 
 obj-$(CONFIG_STM_DUMMY)	+= dummy_stm.o
 
diff --git a/drivers/hwtracing/stm/p_ost.c b/drivers/hwtracing/stm/p_ost.c
new file mode 100644
index 000000000000..fe99b68569d3
--- /dev/null
+++ b/drivers/hwtracing/stm/p_ost.c
@@ -0,0 +1,213 @@ 
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2023 Qualcomm Innovation Center, Inc. All rights reserved.
+ *
+ * MIPI OST framing protocol for STM devices.
+ */
+
+#include <linux/configfs.h>
+#include <linux/module.h>
+#include <linux/device.h>
+#include <linux/slab.h>
+#include <linux/stm.h>
+#include "stm.h"
+
+
+#define OST_TOKEN_STARTSIMPLE		(0x10)
+#define OST_VERSION_MIPI1		(0x10 << 8)
+
+/* entity id to identify the source*/
+#define OST_ENTITY_FTRACE		(0x01 << 16)
+#define OST_ENTITY_CONSOLE		(0x02 << 16)
+
+#define OST_CONTROL_PROTOCOL		(0x0 << 24)
+
+/*
+ * OST Base Protocol Header
+ *
+ * Position	Bits	Field Name
+ *      0       8       STARTSIMPLE
+ *      1       8       Version
+ *      2       8       Entity ID
+ *      3       8       protocol ID
+ */
+#define DATA_HEADER (OST_TOKEN_STARTSIMPLE | OST_VERSION_MIPI1 | \
+			OST_CONTROL_PROTOCOL)
+
+#define STM_MAKE_VERSION(ma, mi)	((ma << 8) | mi)
+#define STM_HEADER_MAGIC		(0x5953)
+
+enum ost_entity_type {
+	OST_ENTITY_TYPE_NONE,
+	OST_ENTITY_TYPE_FTRACE,
+	OST_ENTITY_TYPE_CONSOLE,
+};
+
+static const char * const str_ost_entity_type[] = {
+	[OST_ENTITY_TYPE_NONE]		= "none",
+	[OST_ENTITY_TYPE_FTRACE]	= "ftrace",
+	[OST_ENTITY_TYPE_CONSOLE]	= "console",
+};
+
+struct ost_policy_node {
+	enum ost_entity_type	entity_type;
+};
+
+struct ost_output {
+	struct ost_policy_node	node;
+};
+
+/* Set default entity type as none */
+static void ost_policy_node_init(void *priv)
+{
+	struct ost_policy_node *pn = priv;
+
+	pn->entity_type = OST_ENTITY_TYPE_NONE;
+}
+
+static int ost_output_open(void *priv, struct stm_output *output)
+{
+	struct ost_policy_node *pn = priv;
+	struct ost_output *opriv;
+
+	opriv = kzalloc(sizeof(*opriv), GFP_ATOMIC);
+	if (!opriv)
+		return -ENOMEM;
+
+	memcpy(&opriv->node, pn, sizeof(opriv->node));
+	output->pdrv_private = opriv;
+	return 0;
+}
+
+static void ost_output_close(struct stm_output *output)
+{
+	kfree(output->pdrv_private);
+}
+
+static ssize_t ost_t_policy_entity_show(struct config_item *item,
+				char *page)
+{
+	struct ost_policy_node *pn = to_pdrv_policy_node(item);
+
+	return scnprintf(page, PAGE_SIZE, "%s\n",
+			str_ost_entity_type[pn->entity_type]);
+}
+
+static ssize_t
+ost_t_policy_entity_store(struct config_item *item, const char *page,
+			size_t count)
+{
+	struct mutex *mutexp = &item->ci_group->cg_subsys->su_mutex;
+	struct ost_policy_node *pn = to_pdrv_policy_node(item);
+	char str[10] = "";
+
+	mutex_lock(mutexp);
+	if (sscanf(page, "%s", str) != 1)
+		return -EINVAL;
+	mutex_unlock(mutexp);
+
+	if (!strcmp(str, str_ost_entity_type[OST_ENTITY_TYPE_FTRACE]))
+		pn->entity_type = OST_ENTITY_TYPE_FTRACE;
+	else if (!strcmp(str, str_ost_entity_type[OST_ENTITY_TYPE_CONSOLE]))
+		pn->entity_type = OST_ENTITY_TYPE_CONSOLE;
+	else
+		return -EINVAL;
+	return count;
+}
+CONFIGFS_ATTR(ost_t_policy_, entity);
+
+static ssize_t ost_t_policy_entity_available_show(struct config_item *item,
+				char *page)
+{
+	return scnprintf(page, PAGE_SIZE, "%s\n", "ftrace console");
+}
+CONFIGFS_ATTR_RO(ost_t_policy_, entity_available);
+
+static struct configfs_attribute *ost_t_policy_attrs[] = {
+	&ost_t_policy_attr_entity,
+	&ost_t_policy_attr_entity_available,
+	NULL,
+};
+
+static ssize_t notrace ost_write(struct stm_data *data,
+		struct stm_output *output, unsigned int chan,
+		const char *buf, size_t count)
+{
+	unsigned int c = output->channel + chan;
+	unsigned int m = output->master;
+	const unsigned char nil = 0;
+	u32 header = DATA_HEADER;
+	u8 trc_hdr[16];
+	ssize_t sz;
+
+	struct ost_output *op = output->pdrv_private;
+
+	/*
+	 * Identify the source by entity type.
+	 * If entity type is not set, return error value.
+	 */
+	if (op->node.entity_type == OST_ENTITY_TYPE_FTRACE) {
+		header |= OST_ENTITY_FTRACE;
+	} else if (op->node.entity_type == OST_ENTITY_TYPE_CONSOLE) {
+		header |= OST_ENTITY_CONSOLE;
+	} else {
+		pr_debug("p_ost: Entity must be set for trace data.");
+		return -EINVAL;
+	}
+
+	/*
+	 * STP framing rules for OST frames:
+	 *   * the first packet of the OST frame is marked;
+	 *   * the last packet is a FLAG with timestamped tag.
+	 */
+	/* Message layout: HEADER / DATA / TAIL */
+	/* HEADER */
+	sz = data->packet(data, m, c, STP_PACKET_DATA, STP_PACKET_MARKED,
+			  4, (u8 *)&header);
+	if (sz <= 0)
+		return sz;
+
+	/* DATA */
+	*(u16 *)(trc_hdr) = STM_MAKE_VERSION(0, 4);
+	*(u16 *)(trc_hdr + 2) = STM_HEADER_MAGIC;
+	*(u32 *)(trc_hdr + 4) = raw_smp_processor_id();
+	*(u64 *)(trc_hdr + 8) = task_tgid_nr(get_current());
+	sz = stm_data_write(data, m, c, false, trc_hdr, sizeof(trc_hdr));
+	if (sz <= 0)
+		return sz;
+
+	sz = stm_data_write(data, m, c, false, buf, count);
+
+	/* TAIL */
+	if (sz > 0)
+		data->packet(data, m, c, STP_PACKET_FLAG,
+			STP_PACKET_TIMESTAMPED, 0, &nil);
+
+	return sz;
+}
+
+static const struct stm_protocol_driver ost_pdrv = {
+	.owner			= THIS_MODULE,
+	.name			= "p_ost",
+	.write			= ost_write,
+	.policy_attr		= ost_t_policy_attrs,
+	.output_open		= ost_output_open,
+	.output_close		= ost_output_close,
+	.policy_node_init	= ost_policy_node_init,
+};
+
+static int ost_stm_init(void)
+{
+	return stm_register_protocol(&ost_pdrv);
+}
+
+static void ost_stm_exit(void)
+{
+	stm_unregister_protocol(&ost_pdrv);
+}
+
+module_init(ost_stm_init);
+module_exit(ost_stm_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("MIPI Open System Trace STM framing protocol driver");