netdev - Re: [RFC PATCH] net/core: support runtime PM on net

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Date:	Thu, 11 Oct 2012 10:41:12 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Oliver Neukum <oneukum@...e.de>
Cc:	"David S. Miller" <davem@...emloft.net>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>, netdev@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [RFC PATCH] net/core: support runtime PM on net_device

Oliver, sorry for not CC list.

On Wed, Oct 10, 2012 at 9:17 PM, Oliver Neukum <oneukum@...e.de> wrote:
> On Wednesday 10 October 2012 20:58:33 Ming Lei wrote:
>> In ioctl path on net_device, the physical deivce is often
>> touched, but the physical device may have been put into runtime
>> suspend state already, so cause some utilitis(ifconfig, ethtool,
>> ...) to return failure in this situation.
>>
>> This patch enables runtime PM on net_device and mark it as
>> no_callbacks, and resumes the net_device if physical device
>> is to be accessed, then suspends it after completion of the
>> access.
>>
>> This patch fixes the problem above.
>>
>
> [..]
>> +     if (pm_runtime_get_sync(&dev->dev) < 0)
>> +             return -ENODEV;
>
> -EIO would be appropriate.

-ENODEV should be fine, at least some current drivers
return it in this situation.

>
>> +     err = __dev_ifsioc(net, ifr, cmd);
>> +
>> +     pm_runtime_put(&dev->dev);
>> +
>> +     return err;
>> +}
>> +
>>  /*
>>   *   This function handles all "interface"-type I/O control requests. The actual
>>   *   'doing' part of this is dev_ifsioc above.
>> diff --git a/net/core/ethtool.c b/net/core/ethtool.c
>> index 4d64cc2..2dc43da 100644
>> --- a/net/core/ethtool.c
>> +++ b/net/core/ethtool.c
>> @@ -25,6 +25,7 @@
>>  #include <linux/slab.h>
>>  #include <linux/rtnetlink.h>
>>  #include <linux/sched.h>
>> +#include <linux/pm_runtime.h>
>>
>>  /*
>>   * Some useful ethtool_ops methods that're device independent.
>> @@ -1464,10 +1465,13 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>                       return -EPERM;
>>       }
>>
>> +     if ((ret = pm_runtime_get_sync(&dev->dev)) < 0)
>> +             return -ENODEV;
>> +
>>       if (dev->ethtool_ops->begin) {
>
> Perhaps you should check that first.

No, ->begin() may access physical device too, also no matter
->begin is defined or not, the 'cmd' will be sent to device driver.

>
>>               rc = dev->ethtool_ops->begin(dev);
>>               if (rc  < 0)
>> -                     return rc;
>> +                     goto exit;
>>       }
>>       old_features = dev->features;
>>
>> @@ -1648,6 +1652,7 @@ int dev_ethtool(struct net *net, struct ifreq *ifr)
>>
>>       if (old_features != dev->features)
>>               netdev_features_change(dev);
>> -
>> +exit:
>> +     pm_runtime_put(&dev->dev);
>>       return rc;
>>  }
>> diff --git a/net/core/net-sysfs.c b/net/core/net-sysfs.c
>> index bcf02f6..c9adb89 100644
>> --- a/net/core/net-sysfs.c
>> +++ b/net/core/net-sysfs.c
>> @@ -23,6 +23,7 @@
>>  #include <linux/export.h>
>>  #include <linux/jiffies.h>
>>  #include <net/wext.h>
>> +#include <linux/pm_runtime.h>
>>
>>  #include "net-sysfs.h"
>>
>> @@ -1415,6 +1416,9 @@ int netdev_register_kobject(struct net_device *net)
>>       if (error)
>>               return error;
>>
>> +     pm_runtime_no_callbacks(dev);
>> +     pm_runtime_enable(dev);

> Why?

Firstly, 'net_device' is a 'class' device, and its class of 'net_class' doesn't
define runtime pm callback. Also no drivers define its runtime pm callback
in its device_type, so I mark it as no_callback.

Also if not enabling runtime pm for net_device, pm_runtime_get_sync()
will return -EACCESS.

Thanks,
--
Ming Lei
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