platform/surface: aggregator: Improve documentation and handling of message target and source IDs

The `tid_in` and `tid_out` fields of the serial hub protocol command
struct (struct ssh_command) are actually source and target IDs,
indicating the peer from which the message originated and the peer for
which it is intended.

Change the naming of those fields accordingly and improve the protocol
documentation. Additionally, introduce an enum containing all currently
known peers, i.e. targets and sources.

Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Link: https://lore.kernel.org/r/20221202223327.690880-3-luzmaximilian@gmail.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

2 files changed, 21 insertions, 19 deletions

diff --git a/Documentation/driver-api/surface_aggregator/client.rst b/Documentation/driver-api/surface_aggregator/client.rst
index 27f95abdbe99..9d7411223a84 100644
--- a/Documentation/driver-api/surface_aggregator/client.rst
+++ b/Documentation/driver-api/surface_aggregator/client.rst
@@ -191,7 +191,7 @@ data received from it is converted from little-endian to host endianness.
             *       they do not correspond to an actual SAM/EC request.
             */
            rqst.target_category = SSAM_SSH_TC_SAM;
-           rqst.target_id = 0x01;
+           rqst.target_id = SSAM_SSH_TID_SAM;
            rqst.command_id = 0x02;
            rqst.instance_id = 0x03;
            rqst.flags = SSAM_REQUEST_HAS_RESPONSE;
@@ -241,7 +241,7 @@ one of the generator macros, for example via:
 
    SSAM_DEFINE_SYNC_REQUEST_W(__ssam_tmp_perf_mode_set, __le32, {
            .target_category = SSAM_SSH_TC_TMP,
-           .target_id       = 0x01,
+           .target_id       = SSAM_SSH_TID_SAM,
            .command_id      = 0x03,
            .instance_id     = 0x00,
    });
diff --git a/Documentation/driver-api/surface_aggregator/ssh.rst b/Documentation/driver-api/surface_aggregator/ssh.rst
index bf007d6c9873..18fd0f0aee84 100644
--- a/Documentation/driver-api/surface_aggregator/ssh.rst
+++ b/Documentation/driver-api/surface_aggregator/ssh.rst
@@ -13,6 +13,7 @@
 .. |DATA_NSQ| replace:: ``DATA_NSQ``
 .. |TC| replace:: ``TC``
 .. |TID| replace:: ``TID``
+.. |SID| replace:: ``SID``
 .. |IID| replace:: ``IID``
 .. |RQID| replace:: ``RQID``
 .. |CID| replace:: ``CID``
@@ -219,13 +220,13 @@ following fields, packed together and in order:
      - |u8|
      - Target category.
 
-   * - |TID| (out)
+   * - |TID|
      - |u8|
-     - Target ID for outgoing (host to EC) commands.
+     - Target ID for commands/messages.
 
-   * - |TID| (in)
+   * - |SID|
      - |u8|
-     - Target ID for incoming (EC to host) commands.
+     - Source ID for commands/messages.
 
    * - |IID|
      - |u8|
@@ -286,19 +287,20 @@ general, however, a single target category should map to a single reserved
 event request ID.
 
 Furthermore, requests, responses, and events have an associated target ID
-(``TID``). This target ID is split into output (host to EC) and input (EC to
-host) fields, with the respecting other field (e.g. output field on incoming
-messages) set to zero. Two ``TID`` values are known: Primary (``0x01``) and
-secondary (``0x02``). In general, the response to a request should have the
-same ``TID`` value, however, the field (output vs. input) should be used in
-accordance to the direction in which the response is sent (i.e. on the input
-field, as responses are generally sent from the EC to the host).
-
-Note that, even though requests and events should be uniquely identifiable
-by target category and command ID alone, the EC may require specific
-target ID and instance ID values to accept a command. A command that is
-accepted for ``TID=1``, for example, may not be accepted for ``TID=2``
-and vice versa.
+(``TID``) and source ID (``SID``). These two fields indicate where a message
+originates from (``SID``) and what the intended target of the message is
+(``TID``). Note that a response to a specific request therefore has the source
+and target IDs swapped when compared to the original request (i.e. the request
+target is the response source and the request source is the response target).
+See (:c:type:`enum ssh_request_id <ssh_request_id>`) for possible values of
+both.
+
+Note that, even though requests and events should be uniquely identifiable by
+target category and command ID alone, the EC may require specific target ID and
+instance ID values to accept a command. A command that is accepted for
+``TID=1``, for example, may not be accepted for ``TID=2`` and vice versa. While
+this may not always hold in reality, you can think of different target/source
+IDs indicating different physical ECs with potentially different feature sets.
 
 
 Limitations and Observations