Re: [PATCH 2/2] soundwire: Intel: stop sdw clock in system suspend

[Pierre-Louis Bossart]

> If the Manager doesn't send a clock-stop, the peripherals don't get a
> notification that they can enter a lower-power mode. The clock suddenly
> disappears without warning and without the peripherals being notified
> why, so they don't have any information to know what is happening.

that's not quite right, see below.

> The Manager should send a clock-stop notification before stopping the
> clock.

That's exactly the existing logic in drivers/soundwire/bus.c, the core does notify all peripheral drivers of a clock stop transition.

sdw_slave_clk_stop_callback(slave, SDW_CLK_PRE_PREPARE);
sdw_slave_clk_stop_callback(slave, SDW_CLK_POST_PREPARE);

These pre- and post callback that can be used by the peripheral for imp-def actions.

I am not sure if the POST_PREPARE makes sense, since the clock is already stopped the peripheral cannot be programmed. IIRC it was added for symmetry.
The PRE_PREPARE is most likely what you are looking for in the implementation of the drv->ops->clk_stop callback.

Hope this helps!