docs/designs/uart-mux-support.md

13 To support this configuration, obmc-console needs to provide a method for
14 console selection to avoid manually setting GPIOs.
18 There are already [open changes for obmc-console][obmc-console-uart-mux-series]
21 [obmc-console-uart-mux-series]:
22   https://gerrit.openbmc.org/c/openbmc/obmc-console/+/71864
30 - The user can select a console to be muxed
33   console depending on the host state and other information.
35 - It is clear to whoever is reading the logs of that console when a console was
41 - Console selection (implies mux control) must be possible from an external
44 The scope of this change is obmc-console and other projects which rely on the
52 obmc-console:
77    1. The console IO regardless of the mux state
78    2. The console IO isolated to a specific mux port
91   then it can't provide the console IO of another mux port (4.1) as that's
119    the host console.
137 interact with the host console).
142 user connecting to the host console endpoint to immediately disrupt the update
146 on the initiation of a connection (2.3), the user connecting to the host console
149 However, we can presume the user is connecting to the host console endpoint for
158 Should it be the responsibility of obmc-console to coordinate otherwise
166 obmc-console should implement a mechanism to control the mux state, but likely
172 1. The dropbear/obmc-console-client integration exposing consoles via SSH
184 - Assume that a user connecting to the exposed console endpoint wants to select
185   that console if it's behind a mux
197 console. The net result is no behavioural difference from obmc-console
204 Every console will have its own D-Bus name, as this is backwards-compatible with
214 In unified-tree, one console is reachable via the D-Bus name of another,
220 busctl set-property xyz.openbmc_project.Console.host1 \
221 /xyz/openbmc_project/console/host2 \
222 xyz.openbmc_project.Console.Access Connect ""
231 busctl tree --user xyz.openbmc_project.Console.host1
234     └─/xyz/openbmc_project/console
235       ├─/xyz/openbmc_project/console/host1
236       └─/xyz/openbmc_project/console/host2
242 busctl tree --user xyz.openbmc_project.Console.host1
245     └─/xyz/openbmc_project/console
246       └─/xyz/openbmc_project/console/host1
248 busctl tree --user xyz.openbmc_project.Console.host2
251     └─/xyz/openbmc_project/console
252       └─/xyz/openbmc_project/console/host2
259 1. Implement an interface on each console object that defines a boolean `Active`
261    being implemented on the console object, has all the context it needs to
263    property is `true` when the mux is configured for the console of interest,
270    a given console.
281 `Mux` interface (e.g. at `/xyz/openbmc_project/console`). This is desired to
299 To help shape the choices here, we have the existing behaviours of obmc-console
302 1. We already have support for concurrent console server instances
304 2. Concurrent console support is implemented as one obmc-console-server process
307 3. As each Linux TTY device is paired with its obmc-console-server process, each
308    obmc-console-server D-Bus connection needs a unique name
310 4. We use the unique console-ids to name global resources, including both the
313 As in the linked discussion, given the `console-id` value really represents
316 Taking this approach avoids adding a new endpoint ABI to obmc-console and
356   https://gerrit.openbmc.org/c/openbmc/obmc-console/+/71228/comment/62a5fce9_60c3ad3e/
358   https://gerrit.openbmc.org/c/openbmc/obmc-console/+/71867/comment/756f0abe_5ebe8d66/
367 achieves the desired console behaviour. It's worth noting that design option `F`
376 It's proposed that we use one obmc-console-server process to expose the `N`
377 consoles connected to a UART mux, where each console represents one mux port.
382 The internal datastructures of obmc-console will change to accomodate the
407 | xyz.openbmc_project.Console.host1 +-----+         +-----+ ttyS0 +-----+ UART0 +-----+     |     +…
410                                           | console |                                 | MUX |
413 | xyz.openbmc_project.Console.host2 +-----+         +-------------------+ GPIO  +-----+     |     +…
421 To inform people who may be reading log files for a console, connection and
422 disconnection events of a console via mux control will produce messages for
427 - Making it clear this message is from obmc-console
438 [obmc-console] %Y-%m-%d %H:%M:%S UTC CONNECTED
439 [obmc-console] %Y-%m-%d %H:%M:%S UTC DISCONNECTED
455 ### Multiple obmc-console-server processes for the multiple consoles
483   obmc-console, docs