Re: [PATCH v3 3/5] soundwire: stream: allow flagged BPT firmware download while streams are idle

[Pierre-Louis Bossart <pierre-louis.bossart@linux.dev>]

> diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h
> index f710e5932b4b..9a3904f42078 100644
> --- a/include/linux/soundwire/sdw.h
> +++ b/include/linux/soundwire/sdw.h
> @@ -1005,6 +1005,19 @@ struct sdw_stream_runtime {
>   * @bpt_stream_refcount: number of BTP streams currently using this bus (should
>   * be zero or one, multiple streams per link is not supported).
>   * @bpt_stream: pointer stored to handle BTP streams.
> + * @bpt_fw_download: set by a BPT-capable manager to flag a resume-time firmware
> + * download (BPT/BRA). BPT and active audio are mutually exclusive on the bus;
> + * this flag marks the one narrow exception -- a power-off-mode resume where the
> + * codec must re-download firmware over BPT before its stream (left DISABLED
> + * across suspend) is re-enabled. The manager guarantees no audio stream is made
> + * active on the bus for the duration, so sdw_master_rt_alloc() permits the BPT
> + * allocation even when idle audio streams are still allocated; an actively
> + * streaming audio stream (PREPARED/ENABLED) still blocks BPT. It is not a
> + * mechanism for running audio concurrently with a download. Written with
> + * WRITE_ONCE() by the manager before it enters the stream allocation path and
> + * cleared (also WRITE_ONCE()) after the transfer; read with READ_ONCE() in
> + * sdw_master_rt_alloc() under bus_lock. Single-BPT exclusivity
> + * (bpt_stream_refcount) means no concurrent writer races the lock-protected read.
>   * @ops: Master callback ops
>   * @port_ops: Master port callback ops
>   * @prop: Master properties
> @@ -1045,6 +1058,7 @@ struct sdw_bus {
>  	int stream_refcount;
>  	int bpt_stream_refcount;
>  	struct sdw_stream_runtime *bpt_stream;
> +	bool bpt_fw_download;

nit-pick: I would add this one line above to leave pointers and
structures grouped, this would be nicer in terms of alignment.

>  	const struct sdw_master_ops *ops;
>  	const struct sdw_master_port_ops *port_ops;
>  	struct sdw_master_prop prop;