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

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Message-ID: <6dde3b32-a29a-3ac9-d95d-283f5b05e64a@linux.intel.com>
Date:   Tue, 17 Mar 2020 08:19:34 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        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 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.