linux-kernel - Re: [PATCH v2 1/3] ALSA: compress: document the compress audio state machine

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Message-ID: <20200622151334.GW71940@ediswmail.ad.cirrus.com>
Date:   Mon, 22 Jun 2020 15:13:34 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
CC:     Vinod Koul <vkoul@...nel.org>, Takashi Iwai <tiwai@...e.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        <alsa-devel@...a-project.org>, <linux-arm-msm@...r.kernel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] ALSA: compress: document the compress audio state
 machine

On Mon, Jun 22, 2020 at 08:28:48AM -0500, Pierre-Louis Bossart wrote:
> On 6/22/20 1:58 AM, Vinod Koul wrote:
> >+                                        +----------+
> >+                                        |          |
> >+                                        |   OPEN   |
> >+                                        |          |
> >+                                        +----------+
> >+                                             |
> >+                                             |
> >+                                             | compr_set_params()
> >+                                             |
> >+                                             v
> >+         compr_free()                   +----------+
> >+  +-------------------------------------|          |
> >+  |                                     |   SETUP  |
> >+  |           +------------------------>|          |<---------------------------------+
> >+  |           | compr_drain_notify()    +----------+                                  |
> >+  |           |                              |                                        |
> >+  |           |                              |                                        |
> >+  |           |                              | compr_write()                          |
> >+  |           |                              |                                        |
> >+  |           |                              v                                        |
> >+  |           |                         +----------+                                  |
> >+  |           |                         |          |                                  |
> >+  |           |                         |  PREPARE |                                  |
> >+  |           |                         |          |                                  |
> >+  |           |                         +----------+                                  |
> >+  |           |                              |                                        |
> >+  |           |                              |                                        |
> >+  |           |                              | compr_start()                          |
> >+  |           |                              |                                        |
> >+  |           |                              v                                        |
> >+  |     +----------+                    +----------+  compr_pause()  +----------+     |
> >+  |     |          |    compr_drain()   |          |---------------->|          |     |
> >+  |     |  DRAIN   |<-------------------|  RUNNING |                 |  PAUSE   |     |
> >+  |     |          |                    |          |<----------------|          |     |
> >+  |     +----------+                    +----------+  compr_resume() +----------+     |
> >+  |           |                           |      |                                    |
> >+  |           |                           |      |                                    |
> >+  |           |                           |      |                                    |
> >+  |           |                           |      |          compr_stop()              |
> >+  |           |                           |      +------------------------------------+
> >+  |           |       +----------+        |
> >+  |           |       |          |        |
> >+  +-----------+------>|          |<-------+
> >+     compr_free()     |   FREE   |  compr_free()
> >+                      |          |
> >+                      +----------+
> a) can you clarify if we can go from running to free directly? is
> this really a legit transition? There's already the option of doing
> a stop and a a drain.
> 

This is allowed in the current code, the kernel sends the stop
internally in this case, so it kinda does go through the setup
state just not from the users view point. I am not sure I have a
good handle on if that makes sense or not.

> c) no way to stop a paused stream?

Currently the code does allow this and it certainly makes sense
so should probably be added.

Thanks,
Charles