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

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Date:	Fri, 24 Apr 2015 09:19:55 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	David Miller <davem@...emloft.net>
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

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.
-- 
Florian
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