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Message-ID: <c978a8b8-7373-4ecd-8a64-84b712b49926@quicinc.com>
Date: Fri, 14 Nov 2025 14:05:46 +0800
From: "Yingchao Deng (Consultant)" <quic_yingdeng@...cinc.com>
To: Yingchao Deng <yingchao.deng@....qualcomm.com>,
Steven Rostedt
<rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
"Mathieu
Desnoyers" <mathieu.desnoyers@...icios.com>,
Jonathan Corbet
<corbet@....net>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Maxime Coquelin <mcoquelin.stm32@...il.com>,
Alexandre Torgue
<alexandre.torgue@...s.st.com>
CC: <linux-kernel@...r.kernel.org>, <linux-trace-kernel@...r.kernel.org>,
<linux-doc@...r.kernel.org>,
<linux-stm32@...md-mailman.stormreply.com>,
<linux-arm-kernel@...ts.infradead.org>,
Tingwei Zhang
<tingwei.zhang@....qualcomm.com>,
Yuanfang Zhang
<yuanfang.zhang@....qualcomm.com>,
Jinlong Mao <jinlong.mao@....qualcomm.com>
Subject: Re: [PATCH v4] stm: class: Add MIPI OST protocol support
On 10/24/2025 3:05 PM, Yingchao Deng wrote:
> 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.
>
> 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.
>
> Signed-off-by: Tingwei Zhang <tingwei.zhang@....qualcomm.com>
> Signed-off-by: Yuanfang Zhang <yuanfang.zhang@....qualcomm.com>
> Signed-off-by: Jinlong Mao <jinlong.mao@....qualcomm.com>
> Signed-off-by: Yingchao Deng <yingchao.deng@....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 | 6 +
> Documentation/trace/p_ost.rst | 36 ++++
> drivers/hwtracing/stm/Kconfig | 14 ++
> drivers/hwtracing/stm/Makefile | 2 +
> drivers/hwtracing/stm/p_ost.c | 236 +++++++++++++++++++++
> 5 files changed, 294 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..498739b49da0
> --- /dev/null
> +++ b/Documentation/ABI/testing/configfs-stp-policy-p_ost
> @@ -0,0 +1,6 @@
> +What: /config/stp-policy/<device>:p_ost.<policy>/<node>/entity
> +Date: Oct 2025
> +KernelVersion: 6.18
> +Description:
> + Set the entity which is to identify the source, RW.
> +
> diff --git a/Documentation/trace/p_ost.rst b/Documentation/trace/p_ost.rst
> new file mode 100644
> index 000000000000..df93b889eb4c
> --- /dev/null
> +++ b/Documentation/trace/p_ost.rst
> @@ -0,0 +1,36 @@
> +.. 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".
> +
> +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, console and diag entity.
> +
> +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 that p_ost supports:
> +# 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 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..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..ac9492ed5c2c
> --- /dev/null
> +++ b/drivers/hwtracing/stm/p_ost.c
> @@ -0,0 +1,236 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2025 Qualcomm Innovation Center, Inc. All rights reserved.
> + *
> + * 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_PROTOCOL) | \
> + (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(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);
> + 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 ost_policy_node *pn = to_pdrv_policy_node(item);
> + int i;
> +
> + i = entity_index(page);
> + if (i)
> + pn->entity_type = i;
> + 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];
> + 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",
> + .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: efb26a23ed5f5dc3554886ab398f559dcb1de96b
> change-id: 20251024-p_ost-d5052b4a3173
>
> Best regards,
Gentle reminder.
thanks,
Yingchao.
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