Re: [PATCH V6 8/8] soundwire: amd: add pm_prepare callback and pm ops support

["Mukunda,Vijendar" <vijendar.mukunda@amd.com>]

On 07/03/23 20:58, Pierre-Louis Bossart wrote:
>> +static int amd_resume_child_device(struct device *dev, void *data)
>> +{
>> +	struct sdw_slave *slave = dev_to_sdw_dev(dev);
>> +	int ret;
>> +
>> +	if (!slave->probed) {
>> +		dev_dbg(dev, "skipping device, no probed driver\n");
>> +		return 0;
>> +	}
>> +	if (!slave->dev_num_sticky) {
>> +		dev_dbg(dev, "skipping device, never detected on bus\n");
>> +		return 0;
>> +	}
>> +	if (!pm_runtime_suspended(dev))
>> +		return 0;
>> +	ret = pm_request_resume(dev);
> I still don't get why the test above was needed. It's racy and brings
> limited benefits.
As explained below thread,

https://lore.kernel.org/lkml/acd3a560-1218-9f1d-06ec-19e4d3d4e2c9@amd.com

Our scenario is multiple peripheral devices are connected
over the same link.

In our implementation, device_for_each_child() function invokes
amd_resume_child_device callback for each child.
When any one of the child device is active, It will break the
iteration, which results in failure resuming all child devices.

If we skip , pm_suspended check , it will not resume all
peripheral devices when any one of the peripheral device is active.
>
>> +	if (ret < 0)
>> +		dev_err(dev, "pm_request_resume failed: %d\n", ret);
>> +
>> +	return ret;
>> +}