linux-kernel - Re: [PATCH v1 10/11] ALSA: hda: cs35l41: Add device_link between HDA and cs35l41

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Message-ID: <bf6b5496-bcf9-771d-5921-fe137fa3bec0@opensource.cirrus.com>
Date:   Fri, 21 Jul 2023 15:55:43 +0100
From:   Stefan Binding <sbinding@...nsource.cirrus.com>
To:     Takashi Iwai <tiwai@...e.de>
CC:     Mark Brown <broonie@...nel.org>, Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, <alsa-devel@...a-project.org>,
        <linux-kernel@...r.kernel.org>, <patches@...nsource.cirrus.com>
Subject: Re: [PATCH v1 10/11] ALSA: hda: cs35l41: Add device_link between HDA
 and cs35l41_hda


On 20/07/2023 15:21, Takashi Iwai wrote:
> On Thu, 20 Jul 2023 15:31:46 +0200,
> Stefan Binding wrote:
>> To ensure consistency between the HDA core and the CS35L41 HDA
>> driver, add a device_link between them. This ensures that the
>> HDA core will suspend first, and resume second, meaning the
>> amp driver will not miss any events from the playback hook from
>> the HDA core during system suspend and resume.
>>
>> Signed-off-by: Stefan Binding <sbinding@...nsource.cirrus.com>
>> ---
>>   sound/pci/hda/cs35l41_hda.c | 13 ++++++++++++-
>>   1 file changed, 12 insertions(+), 1 deletion(-)
>>
>> diff --git a/sound/pci/hda/cs35l41_hda.c b/sound/pci/hda/cs35l41_hda.c
>> index 70aa819cfbd64..175378cdf9dfa 100644
>> --- a/sound/pci/hda/cs35l41_hda.c
>> +++ b/sound/pci/hda/cs35l41_hda.c
>> @@ -1063,6 +1063,7 @@ static int cs35l41_hda_bind(struct device *dev, struct device *master, void *mas
>>   {
>>   	struct cs35l41_hda *cs35l41 = dev_get_drvdata(dev);
>>   	struct hda_component *comps = master_data;
>> +	unsigned int sleep_flags;
>>   	int ret = 0;
>>   
>>   	if (!comps || cs35l41->index < 0 || cs35l41->index >= HDA_MAX_COMPONENTS)
>> @@ -1102,6 +1103,11 @@ static int cs35l41_hda_bind(struct device *dev, struct device *master, void *mas
>>   
>>   	mutex_unlock(&cs35l41->fw_mutex);
>>   
>> +	sleep_flags = lock_system_sleep();
>> +	if (!device_link_add(&comps->codec->core.dev, cs35l41->dev, DL_FLAG_STATELESS))
>> +		dev_warn(dev, "Unable to create device link\n");
>> +	unlock_system_sleep(sleep_flags);
> Is lock_system_sleep() mandatory for device_link_add()?  The function
> takes its rw lock for the race, I suppose.

I believe this is mandatory, to ensure we don't try to add the device 
link during a suspend/resume transition.
Its probably unlikely that that would occur during the component bind, 
but just in case.

Thanks,

Stefan

>
>
> thanks,
>
> Takashi