87 lines
3.0 KiB
Diff
87 lines
3.0 KiB
Diff
From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Alexander Shishkin <alexander.shishkin@linux.intel.com>
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Date: Fri, 5 Oct 2018 15:43:01 +0300
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Subject: [PATCH] stm class: Document the MIPI SyS-T protocol usage
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Add a document describing MIPI SyS-T protocol driver usage.
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Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
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Tested-by: Mathieu Poirier <mathieu.poirier@linaro.org>
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Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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---
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Documentation/trace/sys-t.rst | 62 +++++++++++++++++++++++++++++++++++
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1 file changed, 62 insertions(+)
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create mode 100644 Documentation/trace/sys-t.rst
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diff --git a/Documentation/trace/sys-t.rst b/Documentation/trace/sys-t.rst
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new file mode 100644
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index 000000000000..3d8eb92735e9
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--- /dev/null
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+++ b/Documentation/trace/sys-t.rst
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@@ -0,0 +1,62 @@
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+.. SPDX-License-Identifier: GPL-2.0
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+
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+===================
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+MIPI SyS-T over STP
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+===================
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+
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+The MIPI SyS-T protocol driver can be used with STM class devices to
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+generate standardized trace stream. Aside from being a standard, it
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+provides better trace source identification and timestamp correlation.
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+
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+In order to use the MIPI SyS-T protocol driver with your STM device,
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+first, you'll need CONFIG_STM_PROTO_SYS_T.
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+
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+Now, you can select which protocol driver you want to use when you create
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+a policy for your STM device, by specifying it in the policy name:
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+
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+# mkdir /config/stp-policy/dummy_stm.0:p_sys-t.my-policy/
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+
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+In other words, the policy name format is extended like this:
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+
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+ <device_name>:<protocol_name>.<policy_name>
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+
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+With Intel TH, therefore it can look like "0-sth:p_sys-t.my-policy".
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+
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+If the protocol name is omitted, the STM class will chose whichever
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+protocol driver was loaded first.
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+
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+You can also double check that everything is working as expected by
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+
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+# cat /config/stp-policy/dummy_stm.0:p_sys-t.my-policy/protocol
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+p_sys-t
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+
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+Now, with the MIPI SyS-T protocol driver, each policy node in the
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+configfs gets a few additional attributes, which determine per-source
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+parameters specific to the protocol:
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+
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+# mkdir /config/stp-policy/dummy_stm.0:p_sys-t.my-policy/default
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+# ls /config/stp-policy/dummy_stm.0:p_sys-t.my-policy/default
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+channels
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+clocksync_interval
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+do_len
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+masters
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+ts_interval
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+uuid
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+
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+The most important one here is the "uuid", which determines the UUID
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+that will be used to tag all data coming from this source. It is
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+automatically generated when a new node is created, but it is likely
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+that you would want to change it.
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+
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+do_len switches on/off the additional "payload length" field in the
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+MIPI SyS-T message header. It is off by default as the STP already
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+marks message boundaries.
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+
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+ts_interval and clocksync_interval determine how much time in milliseconds
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+can pass before we need to include a protocol (not transport, aka STP)
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+timestamp in a message header or send a CLOCKSYNC packet, respectively.
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+
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+See Documentation/ABI/testing/configfs-stp-policy-p_sys-t for more
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+details.
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+
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+* [1] https://www.mipi.org/specifications/sys-t
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--
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https://clearlinux.org
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