.../ABI/testing/configfs-stp-policy-p_ost | 9 + Documentation/trace/index.rst | 1 + Documentation/trace/p_ost.rst | 39 ++++ drivers/hwtracing/stm/Kconfig | 14 ++ drivers/hwtracing/stm/Makefile | 2 + drivers/hwtracing/stm/p_ost.c | 241 +++++++++++++++++++++ 6 files changed, 306 insertions(+)
Add MIPI OST (Open System Trace) protocol support for stm to format the
traces. The OST Protocol abstracts the underlying layers from the sending
and receiving applications, thus removing dependencies on the connection
media and platform implementation.
OST over STP packet consists of Header/Payload/End. Header is designed to
include the information required by all OST packets. Information that is
not shared by all packets is left to the higher layer protocols. Thus, the
OST Protocol Header can be regarded as the first part of a complete OST
Packet Header, while a higher layer header can be regarded as an extension
designed for a specific purpose.
+--------+--------+--------+--------+
| start |version |entity |protocol|
+--------+--------+--------+--------+
| stm version | magic |
+-----------------------------------+
| cpu |
+-----------------------------------+
| timestamp |
| |
+-----------------------------------+
| tgid |
| |
+-----------------------------------+
| payload |
+-----------------------------------+
| ... | end |
+-----------------------------------+
In header, there will be STARTSIMPLE/VERSION/ENTITY/PROTOCOL.
STARTSIMPLE is used to signal the beginning of a simplified OST protocol.
The Version field is a one byte, unsigned number identifying the version
of the OST Protocol. The Entity ID field is a one byte unsigned number
that identifies the source.
Entity ID values (0~239) are defined and controlled by the TS owner, and
shall be unique for the whole TS. The configfs entity attribute allows the
user to configure which Entity ID is associated with each policy node.
The Protocol ID field is a one byte unsigned number identifying the higher
layer protocol of the OST Packet, i.e. identifying the format of the data
after the OST Protocol Header. OST Control Protocol ID value represents
the common control protocol, the remaining Protocol ID values may be used
by any higher layer protocols capable of being transported by the OST
Protocol.
Co-developed-by: Tingwei Zhang <tingwei.zhang@oss.qualcomm.com>
Signed-off-by: Tingwei Zhang <tingwei.zhang@oss.qualcomm.com>
Co-developed-by: Yuanfang Zhang <yuanfang.zhang@oss.qualcomm.com>
Signed-off-by: Yuanfang Zhang <yuanfang.zhang@oss.qualcomm.com>
Co-developed-by: Jinlong Mao <jinlong.mao@oss.qualcomm.com>
Signed-off-by: Jinlong Mao <jinlong.mao@oss.qualcomm.com>
Signed-off-by: Yingchao Deng <yingchao.deng@oss.qualcomm.com>
---
Changes in v6:
1. Rebase on top of linux-next-20260518.
2. Fix Kconfig: 'default CONFIG_STM' -> 'default STM'.
3. Fix documentation grammar issues.
4. Add p_ost entry to Documentation/trace/index.rst.
5. Add missing priv_sz field to stm_protocol_driver registration.
6. Use kzalloc_obj() instead of kzalloc() in ost_output_open().
7. Add mutex protection in entity configfs store handler.
8. Keep the configfs entity attribute: entity ID values (0~239) are
defined and controlled by the TS owner and are deployment-specific.
stm_source_type only carries a small number of in-kernel source
classifications and cannot represent the full range of OST entity
assignments needed in practice. The configfs attribute allows each
policy node to declare its entity.
OST_ENTITY_TYPE_NONE is an enum sentinel (not entity ID 0) that causes
ost_write() to return -EINVAL when no entity is configured, preventing
emission of packets with an unintended entity field.
OST_ENTITY_DIAG (0xEE) is a TS-owner-defined value used by Qualcomm's
diagnostic framework as the standard entity identifier for diagnostic
trace sources.
Link to v5: https://lore.kernel.org/all/20260129-p_ost-v5-1-2b14fff39428@oss.qualcomm.com/
Changes in v5:
1. Add Co-developed-by tag.
2. Use yearless copyright for new file.
- Link to v4: https://lore.kernel.org/all/20251024-p_ost-v4-1-3652a06fd055@oss.qualcomm.com/
Changes in v4:
1. Delete unused variable 'i'.
2. Fix build error: call to undeclared function 'task_tgid_nr'.
Link to v3 - https://lore.kernel.org/all/20251022071834.1658684-1-yingchao.deng@oss.qualcomm.com/
Changes in v3:
1. Add more details about OST.
2. Delete 'entity_available' node, and 'entity' node will show available
and currently selected (shown in square brackets) entity.
3. Removed the usage of config_item->ci_group->cg_subsys->su_mutex.
Link to v2 - https://lore.kernel.org/all/20230419141328.37472-1-quic_jinlmao@quicinc.com/
---
.../ABI/testing/configfs-stp-policy-p_ost | 9 +
Documentation/trace/index.rst | 1 +
Documentation/trace/p_ost.rst | 39 ++++
drivers/hwtracing/stm/Kconfig | 14 ++
drivers/hwtracing/stm/Makefile | 2 +
drivers/hwtracing/stm/p_ost.c | 241 +++++++++++++++++++++
6 files changed, 306 insertions(+)
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..8fb160b50c40
--- /dev/null
+++ b/Documentation/ABI/testing/configfs-stp-policy-p_ost
@@ -0,0 +1,9 @@
+What: /config/stp-policy/<device>:p_ost.<policy>/<node>/entity
+Date: May 2026
+KernelVersion: 7.1
+Description:
+ Set the entity ID which identifies the trace source in the
+ OST packet header. Entity ID values (0~239) are defined by
+ the TS owner. Currently supported values are ftrace, console
+ and diag. RW.
+
diff --git a/Documentation/trace/index.rst b/Documentation/trace/index.rst
index 5d9bf4694d5d..9cd1e0b5af6d 100644
--- a/Documentation/trace/index.rst
+++ b/Documentation/trace/index.rst
@@ -72,6 +72,7 @@ interactions and system performance.
intel_th
stm
sys-t
+ p_ost
coresight/index
rv/index
hisi-ptt
diff --git a/Documentation/trace/p_ost.rst b/Documentation/trace/p_ost.rst
new file mode 100644
index 000000000000..2b92e2229653
--- /dev/null
+++ b/Documentation/trace/p_ost.rst
@@ -0,0 +1,39 @@
+.. 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 a coresight-stm device, it will look like "stm0:p_ost.policy".
+
+With the MIPI OST protocol driver, the attributes for each protocol node are:
+
+# 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 of entities that p_ost supports. Currently
+p_ost supports ftrace, console and diag entities.
+
+Set entity:
+# echo 'ftrace' > /sys/kernel/config/stp-policy/stm0:p_ost.policy/default/entity
+
+Get available and currently selected (shown in square brackets) entity:
+# cat /sys/kernel/config/stp-policy/stm0:p_ost.policy/default/entity
+[ftrace] console diag
+
+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 cd7f0b0f3fbe..4c83da5d95a0 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 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..d9c8615849b9 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..d2174872b761
--- /dev/null
+++ b/drivers/hwtracing/stm/p_ost.c
@@ -0,0 +1,241 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) Qualcomm Technologies, Inc. and/or its subsidiaries.
+ *
+ * MIPI OST framing protocol for STM devices.
+ */
+
+#include <linux/pid.h>
+#include <linux/sched/clock.h>
+#include <linux/slab.h>
+#include <linux/stm.h>
+#include "stm.h"
+
+/*
+ * OST Base Protocol Header
+ *
+ * Position Bits Field Name
+ * 0 8 STARTSIMPLE
+ * 1 8 Version
+ * 2 8 Entity ID
+ * 3 8 Protocol ID
+ */
+#define OST_FIELD_STARTSIMPLE 0
+#define OST_FIELD_VERSION 8
+#define OST_FIELD_ENTITY 16
+#define OST_FIELD_PROTOCOL 24
+
+#define OST_TOKEN_STARTSIMPLE 0x10
+#define OST_VERSION_MIPI1 0x10
+
+/* entity id to identify the source */
+#define OST_ENTITY_FTRACE 0x01
+#define OST_ENTITY_CONSOLE 0x02
+#define OST_ENTITY_DIAG 0xEE
+
+#define OST_CONTROL_PROTOCOL 0x0
+
+#define DATA_HEADER ((OST_TOKEN_STARTSIMPLE << OST_FIELD_STARTSIMPLE) | \
+ (OST_VERSION_MIPI1 << OST_FIELD_VERSION) | \
+ (OST_CONTROL_PROTOCOL << OST_FIELD_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,
+ OST_ENTITY_TYPE_DIAG,
+};
+
+static const char * const str_ost_entity_type[] = {
+ [OST_ENTITY_TYPE_NONE] = "none",
+ [OST_ENTITY_TYPE_FTRACE] = "ftrace",
+ [OST_ENTITY_TYPE_CONSOLE] = "console",
+ [OST_ENTITY_TYPE_DIAG] = "diag",
+};
+
+static const u32 ost_entity_value[] = {
+ [OST_ENTITY_TYPE_NONE] = 0,
+ [OST_ENTITY_TYPE_FTRACE] = OST_ENTITY_FTRACE,
+ [OST_ENTITY_TYPE_CONSOLE] = OST_ENTITY_CONSOLE,
+ [OST_ENTITY_TYPE_DIAG] = OST_ENTITY_DIAG,
+};
+
+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_obj(*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);
+ ssize_t sz = 0;
+ int i;
+
+ for (i = 1; i < ARRAY_SIZE(str_ost_entity_type); i++) {
+ if (i == pn->entity_type)
+ sz += sysfs_emit_at(page, sz, "[%s] ", str_ost_entity_type[i]);
+ else
+ sz += sysfs_emit_at(page, sz, "%s ", str_ost_entity_type[i]);
+ }
+
+ sz += sysfs_emit_at(page, sz, "\n");
+ return sz;
+}
+
+static int entity_index(const char *str)
+{
+ int i;
+
+ for (i = 1; i < ARRAY_SIZE(str_ost_entity_type); i++) {
+ if (sysfs_streq(str, str_ost_entity_type[i]))
+ return i;
+ }
+
+ return 0;
+}
+
+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);
+ int i;
+
+ i = entity_index(page);
+ if (i) {
+ mutex_lock(mutexp);
+ pn->entity_type = i;
+ mutex_unlock(mutexp);
+ } else {
+ return -EINVAL;
+ }
+
+ return count;
+}
+CONFIGFS_ATTR(ost_t_policy_, entity);
+
+static struct configfs_attribute *ost_t_policy_attrs[] = {
+ &ost_t_policy_attr_entity,
+ NULL,
+};
+
+static ssize_t
+notrace ost_write(struct stm_data *data, struct stm_output *output,
+ unsigned int chan, const char *buf, size_t count,
+ struct stm_source_data *source)
+{
+ struct ost_output *op = output->pdrv_private;
+ unsigned int c = output->channel + chan;
+ unsigned int m = output->master;
+ const unsigned char nil = 0;
+ u32 header = DATA_HEADER;
+ struct trc_hdr {
+ u16 version;
+ u16 magic;
+ u32 cpu;
+ u64 timestamp;
+ u64 tgid;
+ } hdr;
+ ssize_t sz;
+
+ /*
+ * Identify the source by entity type.
+ * If entity type is not set, return error value.
+ */
+ if (op->node.entity_type)
+ header |= (ost_entity_value[op->node.entity_type] << OST_FIELD_ENTITY);
+ else
+ 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 */
+ hdr.version = STM_MAKE_VERSION(0, 3);
+ hdr.magic = STM_HEADER_MAGIC;
+ hdr.cpu = raw_smp_processor_id();
+ hdr.timestamp = sched_clock();
+ hdr.tgid = task_tgid_nr(current);
+ sz = stm_data_write(data, m, c, false, &hdr, sizeof(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",
+ .priv_sz = sizeof(struct ost_policy_node),
+ .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);
+}
+module_init(ost_stm_init);
+
+static void ost_stm_exit(void)
+{
+ stm_unregister_protocol(&ost_pdrv);
+}
+module_exit(ost_stm_exit);
+
+MODULE_LICENSE("GPL");
+MODULE_DESCRIPTION("MIPI Open System Trace STM framing protocol driver");
---
base-commit: 80dd246accce631c328ea43294e53b2b2dd2aa32
change-id: 20260521-stm_p_ost-3489f42a9e8c
Best regards,
--
Yingchao Deng <yingchao.deng@oss.qualcomm.com>© 2016 - 2026 Red Hat, Inc.