linux-kernel - Re: [PATCH] ALSA: hda: cs35l56: Perform firmware download in the background

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Date: Thu, 2 May 2024 10:21:36 +0100
From: Richard Fitzgerald <rf@...nsource.cirrus.com>
To: Takashi Iwai <tiwai@...e.de>, Simon Trimmer <simont@...nsource.cirrus.com>
CC: <tiwai@...e.com>, <linux-sound@...r.kernel.org>,
        <alsa-devel@...a-project.org>, <linux-kernel@...r.kernel.org>,
        <patches@...nsource.cirrus.com>
Subject: Re: [PATCH] ALSA: hda: cs35l56: Perform firmware download in the
 background

On 02/05/2024 08:34, Takashi Iwai wrote:
> On Wed, 01 May 2024 13:17:55 +0200,
> Simon Trimmer wrote:
>> @@ -964,6 +1011,14 @@ int cs35l56_hda_common_probe(struct cs35l56_hda *cs35l56, int hid, int id)
>>   	mutex_init(&cs35l56->base.irq_lock);
>>   	dev_set_drvdata(cs35l56->base.dev, cs35l56);
>>   
>> +	cs35l56->dsp_wq = create_singlethread_workqueue("cs35l56-dsp");
>> +	if (!cs35l56->dsp_wq) {
>> +		ret = -ENOMEM;
>> +		goto err;
>> +	}
> 
> Do we really need a dedicated workqueue?  In most usages, simple
> schedule_work*() works fine and is recommended.
> 

On a slow I2C bus with 4 amps this work could take over 2 seconds.
That seems too long to be blocking a global system queue. We use a
dedicated queue in the ASoC driver.

Also if we queue work on an ordered (single-threaded) system queue the
firmware won't be downloaded to multiple amps in parallel, so we don't
get the best use of the available bus bandwidth.

> 
> thanks,
> 
> Takashi