linux-kernel - Re: [PATCH V6 8/8] soundwire: amd: add pm

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Date:   Wed, 8 Mar 2023 01:55:39 +0530
From:   "Mukunda,Vijendar" <vijendar.mukunda@....com>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        vkoul@...nel.org
Cc:     alsa-devel@...a-project.org, Basavaraj.Hiregoudar@....com,
        Sunil-kumar.Dommati@....com, Mario.Limonciello@....com,
        amadeuszx.slawinski@...ux.intel.com, Mastan.Katragadda@....com,
        Arungopal.kondaveeti@....com, claudiu.beznea@...rochip.com,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Sanyog Kale <sanyog.r.kale@...el.com>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V6 8/8] soundwire: amd: add pm_prepare callback and pm ops
 support

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;
>> +}