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From: Jaroslav Kysela <perex@perex.cz>
To: Vinod Koul <vkoul@kernel.org>
Cc: alsa-devel@alsa-project.org, khw0178.kim@samsung.com,
	lgirdwood@gmail.com, Takashi Iwai <tiwai@suse.de>,
	s47.kang@samsung.com, tiwai@suse.com,
	'Pierre-Louis Bossart' <pierre-louis.bossart@linux.intel.com>,
	kimty@samsung.com, hmseo@samsung.com,
	Gyeongtaek Lee <gt82.lee@samsung.com>,
	pilsun.jang@samsung.com, tkjung@samsung.com
Subject: Re: [PATCH] ALSA: compress: allow pause and resume during draining
Date: Mon, 12 Oct 2020 16:10:10 +0200
Message-ID: <777e0046-1e3a-e702-c070-cac4c0525ccd@perex.cz> (raw)
In-Reply-To: <20201012135540.GK2968@vkoul-mobl>

Dne 12. 10. 20 v 15:55 Vinod Koul napsal(a):
> On 12-10-20, 15:29, Jaroslav Kysela wrote:
>> Dne 12. 10. 20 v 14:24 Vinod Koul napsal(a):
>>> On 12-10-20, 09:01, Takashi Iwai wrote:
>>>> On Mon, 12 Oct 2020 07:25:25 +0200,
>>>
>>>>> So what if we add another state but keep it in kernel (hidden from
>>>>> userspace)...?
>>>>
>>>> That's fine, then it's just a kernel's business, and it should be
>>>> determined which one makes the code better.
>>>>
>>>> But, there are things to be considered, though:
>>>>
>>>> - SNDRV_PCM_STATE_* is defined as snd_pcm_state_t with __bitwise.
>>>>   This indicates that the type has to be defined in that way
>>>>   explicitly.
>>>>
>>>> - Having a value over SNDRV_PCM_STATE_LAST internally is hackish.
>>>>
>>>>> Right now tinycompress does not make use of PCM streams, kernel handles
>>>>> these. I am not aware of any other implementation.
>>>>>
>>>>> So if the scope if within compress then it might work...
>>>>
>>>> Yes.  But currently the API uses SND_PCM_* even for the compress
>>>> stuff.  Changing this value means to have influence on PCM, even if
>>>> PCM stuff doesn't use it yet.  (At least you'd need to increase
>>>> SND_PCM_STATE_LAST, for example.)
>>>>
>>>> That said, if we want to change only for compress API by assuming that
>>>> the impact must be negligible, the first step would be to move from
>>>> SND_PCM_STATE_* to the own state, SND_COMPRESS_STATE_*.  The values
>>>> should be compatible, but this has to be changed at first.  Then you
>>>> can introduce a new value there.
>>>
>>> I think that sounds reasonable to me, we should not have used
>>> SNDRV_PCM_STATE_* in the first place and long term fix for this should
>>> be SNDRV_COMPRESS_STATE_
>>>
>>> I will cook a patch for this
>>
>> Although the impact is not high, I do think that we should enable the new
>> behaviour conditionally (when the user space asks for it) even if the state
>> values are split. I think that the whole thread is about 'how to extend the
>> current APIs'. The hidden way is really not so nice.
>>
>> Unfortunately, there are no reserved fields in the snd_compr_params structure
>> for this, but I see the similarity with the 'no_wake_mode' field which
>> controls the driver behaviour.
> 
> I was not really thinking of exporting the states to userspace.
> Tinycompress does not use it, I do not see any uses of it to enable
> userspace with it.. Do you think it should be exposed? If so why..?

I don't think that it's required to expose the state for the compressed API to
add this new feature. I just talk about to activate the new feature
conditionally. The question is how to extend the API now.

> Worst case we add an ioctl to query the state.. the state transitions
> are anyway result of control ops on the stream
> 
> Btw what was the motivation for pcm to expose the stream states..?

The driver may change the state when underrun / overrun or an I/O error occurs
and there's also mmap write/read mode, so the traditional read/write with an
error code handling does not work here. Also, the user space should know the
state anyway, so it's better to have all parts synced.

						Jaroslav

-- 
Jaroslav Kysela <perex@perex.cz>
Linux Sound Maintainer; ALSA Project; Red Hat, Inc.

  reply index

Thread overview: 37+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <CGME20200929084051epcas2p35fb2228ed1bdfce6a7ddf5b37c944823@epcas2p3.samsung.com>
2020-09-29  8:40 ` Gyeongtaek Lee
2020-09-29  8:54   ` Takashi Iwai
2020-09-29  9:17     ` Gyeongtaek Lee
2020-09-29 14:00       ` Pierre-Louis Bossart
2020-10-01 10:29     ` Vinod Koul
2020-10-01 15:28       ` Pierre-Louis Bossart
2020-10-06  6:21         ` Vinod Koul
2020-10-06 14:57           ` Pierre-Louis Bossart
2020-10-08  9:49             ` Gyeongtaek Lee
2020-10-09 15:13               ` Takashi Iwai
2020-10-09 17:43                 ` Jaroslav Kysela
2020-10-10  9:08                   ` Takashi Iwai
2020-10-12  5:25                     ` Vinod Koul
2020-10-12  7:01                       ` Takashi Iwai
2020-10-12 12:24                         ` Vinod Koul
2020-10-12 13:29                           ` Jaroslav Kysela
2020-10-12 13:55                             ` Vinod Koul
2020-10-12 14:10                               ` Jaroslav Kysela [this message]
2020-10-12 14:21                                 ` Takashi Iwai
2020-10-12 14:46                                   ` Jaroslav Kysela
2020-10-12 14:59                                     ` Takashi Iwai
2020-10-15 10:47                                       ` Gyeongtaek Lee
2020-10-20  5:23                                         ` Gyeongtaek Lee
2020-10-26  9:18                                         ` Gyeongtaek Lee
2020-10-26 17:01                                           ` Takashi Iwai
2020-10-27  1:56                                             ` Gyeongtaek Lee
     [not found] <CGME20200928105009epcas2p4a65d50d9d09800281395a490d1844ef3@epcas2p4.samsung.com>
2020-09-28 10:50 ` Gyeongtaek Lee
2020-09-28 11:13   ` Jaroslav Kysela
2020-09-28 14:34     ` Pierre-Louis Bossart
2020-09-29  1:51       ` Gyeongtaek Lee
2020-09-29  7:12         ` Takashi Iwai
2020-09-29 17:27           ` Jaroslav Kysela
2020-09-30  9:35             ` Takashi Iwai
2020-09-30  9:57               ` Jaroslav Kysela
2020-09-30 10:33                 ` Takashi Iwai
2020-09-30 11:23                   ` Jaroslav Kysela
2020-10-01 10:35               ` Vinod Koul

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