linux-kernel - Re: [alsa-devel] [PATCH v4 06/15] soundwire: add support for sdw_slave

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Date:   Fri, 13 Dec 2019 09:05:37 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        tiwai@...e.de, broonie@...nel.org, vkoul@...nel.org,
        jank@...ence.com, srinivas.kandagatla@...aro.org,
        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>,
        Sanyog Kale <sanyog.r.kale@...el.com>
Subject: Re: [alsa-devel] [PATCH v4 06/15] soundwire: add support for
 sdw_slave_type

On 12/13/19 1:21 AM, Greg KH wrote:
> On Thu, Dec 12, 2019 at 11:04:00PM -0600, Pierre-Louis Bossart wrote:
>> Currently the bus does not have any explicit support for master
>> devices.
>>
>> First add explicit support for sdw_slave_type and error checks if this type
>> is not set.
>>
>> In follow-up patches we can add support for the sdw_md_type (md==Master
>> Device), following the Grey Bus example.
> 
> How are you using greybus as an example of "master devices"?  All you
> are doing here is setting the type of the existing devices, right?

I took your advice to look at GreyBus and used the 'gb host device' as 
the model to implement the 'sdw master' add/startup/remove interfaces we 
needed.

so yes in this patch we just add a type for the slave, the interesting 
part is in the next patches.
>>   static int sdw_uevent(struct device *dev, struct kobj_uevent_env *env)
>>   {
>> -	struct sdw_slave *slave = to_sdw_slave_device(dev);
>> +	struct sdw_slave *slave;
>>   	char modalias[32];
>>   
>> -	sdw_slave_modalias(slave, modalias, sizeof(modalias));
>> +	if (is_sdw_slave(dev)) {
>> +		slave = to_sdw_slave_device(dev);
>> +
>> +		sdw_slave_modalias(slave, modalias, sizeof(modalias));
>>   
>> -	if (add_uevent_var(env, "MODALIAS=%s", modalias))
>> -		return -ENOMEM;
>> +		if (add_uevent_var(env, "MODALIAS=%s", modalias))
>> +			return -ENOMEM;
>> +	} else {
>> +		/* only Slave device type supported */
>> +		dev_warn(dev, "uevent for unknown Soundwire type\n");
>> +		return -EINVAL;
> 
> Right now, this can not happen, right?
> 
> Not a problem, just trying to understand the sequence of patches here...

yes this cannot happen at this point, it's more of a paranoid test. In 
theory a SoundWire solution could enable a 'monitor' device as defined 
in the standard.