linux-kernel - Re: [PATCH] soundwire: stream: only change state if needed

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Date:   Tue, 17 Mar 2020 15:07:45 +0000
From:   Srinivas Kandagatla <srinivas.kandagatla@...aro.org>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        alsa-devel@...a-project.org
Cc:     linux-kernel@...r.kernel.org, tiwai@...e.de, broonie@...nel.org,
        vkoul@...nel.org, gregkh@...uxfoundation.org, jank@...ence.com,
        slawomir.blauciak@...el.com,
        Bard liao <yung-chuan.liao@...ux.intel.com>,
        Rander Wang <rander.wang@...ux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Hui Wang <hui.wang@...onical.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>
Subject: Re: [PATCH] soundwire: stream: only change state if needed



On 17/03/2020 13:19, Pierre-Louis Bossart wrote:
> 
> 
> On 3/17/20 8:04 AM, Srinivas Kandagatla wrote:
>>
>>
>> On 17/03/2020 12:22, Pierre-Louis Bossart wrote:
>>>
>>> The change below would be an error case for Intel, so it's probably 
>>> better if we go with your suggestion. You have a very specific state 
>>> handling due to your power amps and it's probably better to keep it 
>>> platform-specific.
>>
>> Just trying to understand, why would it be error for Intel case?
>>
>> IMO, If stream state is SDW_STREAM_ENABLED that also implicit that its 
>> prepared too. Similar thing with SDW_STREAM_DEPREPARED.
>> Isn't it?
> 
> the stream state is a scalar value, not a mask. The state machine only 
> allows transition from CONFIGURED TO PREPARED or from DEPREPARED TO 
> PREPARED, or DISABLED to PREPARED.
> There is no allowed transition from ENABLED TO PREPARED, you have to go 
> through the DISABLED state and make sure a bank switch occurred, and 
> re-do a bank switch to prepare again.
I agree with you if are on single dai case. Am happy to move to stream 
handling to machine driver for now.

But this also means that in cases like multi-codec its not recommended 
to call sdw_prepare and sdw_enable in a single function from codec.
Which might be worth documenting.

--srini