netdev - Re: [PATCH] net: mdio-gpio: support access that may sleep

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Date:	Fri, 24 Apr 2015 12:25:14 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	f.fainelli@...il.com
Cc:	vivien.didelot@...oirfairelinux.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, kernel@...oirfairelinux.com
Subject: Re: [PATCH] net: mdio-gpio: support access that may sleep

From: Florian Fainelli <f.fainelli@...il.com>
Date: Fri, 24 Apr 2015 09:19:55 -0700

> On 24/04/15 09:01, David Miller wrote:
>> From: Florian Fainelli <f.fainelli@...il.com>
>> Date: Fri, 24 Apr 2015 08:56:34 -0700
>> 
>>> On 24/04/15 08:04, David Miller wrote:
>>>> From: Vivien Didelot <vivien.didelot@...oirfairelinux.com>
>>>> Date: Wed, 22 Apr 2015 13:06:54 -0400
>>>>
>>>>> Some systems using mdio-gpio may use gpio on message based busses, which
>>>>> require sleeping (e.g. gpio from an I2C I/O expander).
>>>>>
>>>>> Since this driver does not use IRQ handler, it is safe to use the
>>>>> _cansleep suffixed gpio accessors.
>>>>>
>>>>> Signed-off-by: Vivien Didelot <vivien.didelot@...oirfairelinux.com>
>>>>
>>>> Since this is down underneath the layer of an MII bus, you cannot
>>>> universally say that these routines are always called in a sleepable
>>>> context.
>>>>
>>>> The PHY layer, and the driver itself above that, might call these
>>>> routines from timers, interruptes etc.
>>>
>>> The PHY library calls these routines from its state machine workqueue
>>> for that reason, or from process context (when invoked via ethtool
>>> ioctl). The only special case is phy_mac_interrupt() which is callable
>>> from interrupt context, but schedules the state machine workqueue anyway
>>> to circumvent the "in-interrupt" context.
>>>
>>> If we were not doing that, there would be a number of things broken, for
>>> instance the per-MDIO bus mutex would not protect us from anything.
>> 
>> Does the link state polling timer use a workqueue in this manner as
>> well?
> 
> Yes, the state machine re-schedules its own delayed workqueue at the end
> of its state processing, no timer/hrtimer is used.

Ok, thanks for explaining.

I'm apply this patch, therefore, thanks.
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