Re: [RFC PATCH 08/16] soundwire: bus: add bpt_stream pointer

[Vinod Koul <vkoul@xxxxxxxxxx>]

On 18-12-23, 14:20, Pierre-Louis Bossart wrote:
> 
> 
> On 12/18/23 05:55, Vinod Koul wrote:
> > On 07-12-23, 16:29, Pierre-Louis Bossart wrote:
> >> Add a convenience pointer to the 'sdw_bus' structure. BPT is a
> >> dedicated stream which will typically not be handled by DAIs or
> >> dailinks. Since there's only one BPT stream per link, storing the
> >> pointer at the link level seems rather natural.
> >>
> >> Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxxxxxxxx>
> >> ---
> >>  include/linux/soundwire/sdw.h | 2 ++
> >>  1 file changed, 2 insertions(+)
> >>
> >> diff --git a/include/linux/soundwire/sdw.h b/include/linux/soundwire/sdw.h
> >> index e54c5bbd2b91..8db0cd7d0d89 100644
> >> --- a/include/linux/soundwire/sdw.h
> >> +++ b/include/linux/soundwire/sdw.h
> >> @@ -965,6 +965,7 @@ struct sdw_master_ops {
> >>   * @stream_refcount: number of streams currently using this bus
> >>   * @btp_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 for convenience.
> >>   */
> >>  struct sdw_bus {
> >>  	struct device *dev;
> >> @@ -996,6 +997,7 @@ struct sdw_bus {
> >>  	int hw_sync_min_links;
> >>  	int stream_refcount;
> >>  	int bpt_stream_refcount;
> >> +	struct sdw_stream_runtime *bpt_stream;
> > 
> > So we are limiting to single stream? Can we have multiple transfers
> > queued up, which I guess might imply multiple streams?
> 
> 
> Yes for now there is a BTP/BRA single stream active when there are no
> audio transfers taking place. This is the only way to guarantee
> predictable download/resume times.
> 
> There is no mechanism to queue up transfers, be it from the same
> peripheral device or different ones. It would be up to the peripheral
> driver to wait for the BTP stream to be available.
> 
> Adding a queuing mechanism is a bridge too far for now, most platforms
> only have 1 or 2 devices only, and a peripheral driver may or may not be
> ok with delayed downloads. For now the main ask is to reduce download
> times, a single stream is already a good start. There are other
> refinements we need to add as well, such as changing clocks to use the
> fastest gear. I'd like to proceed with baby steps...

Since the API is async in nature, I think it is very reasonable that we
add the queue support (a simple list would do) and notify when the
transfer is complete..

-- 
~Vinod