From: "Morales, Alejandra" <alejandra.morales@tum.de>
To: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Questions about Runtime Power Management
Thread-Topic: Questions about Runtime Power Management
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Date: Sun, 9 Jun 2013 16:28:21 +0000
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Dear all,

I am currently involved in the implementation of my master thesis, for what I am trying to create a user space power management tool. As a part of this work I am developing a kernel module, and one of the first things I need to do is getting the current power state of some devices of my computer, essentially hard drives and network devices (ethernet and wireless cards).

For the hard drives, I get the pointers to the struct device that represents each one iterating over scsi_bus_type and selecting those whose driver is named "sd". Then, I obtain the runtime power state:

dev->power.runtime_status;

I did a test with an external USB hard drive, checking the runtime power state before and after issuing a sleep command with hdparm -Y. The drive effectively spinned down, but the runtime power state didn't change from active to suspended.

In the case of net devices, I get the corresponding structures this way:

struct net_device *netdev = first_net_device(&init_net);
? ??
while (netdev) {

        struct device *dev = &netdev->dev;
? ? ? ??
        /* code... */

        netdev = next_net_device(netdev);
}

For every net_device I get its embedded struct device and then I check the same field as before, but in this case runtime power management is disabled, so I always get the device is suspended, even though it is configured and working properly. In fact, the whole device struct seems to be empty. ?

Taking this into account, my questions are:

- Is it possible that I am not getting the correct struct device for every hardware device?
- Am I checking the correct field of the struct dev_pm_info?
- Do scsi device drivers implement the runtime_status updates when drives effectively change their state?
- Is runtime power management supported by net devices?

Any answer would be really appreciated. Thanks in advance.

Best regards,

Alejandra Morales Ruiz
Master Thesis Student
Technische Universit?t M?nchen
Fakult?t f?r Informatik
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