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

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Message-ID: <553A8099.5000705@cogentembedded.com>
Date:	Fri, 24 Apr 2015 20:42:49 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Florian Fainelli <f.fainelli@...il.com>,
	David Miller <davem@...emloft.net>,
	vivien.didelot@...oirfairelinux.com
CC:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kernel@...oirfairelinux.com
Subject: Re: [PATCH] net: mdio-gpio: support access that may sleep

On 04/24/2015 08:36 PM, Florian Fainelli wrote:

>>>>> 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,

>>     It is not (as we have discussed recently) -- cancel_work_sync() may
>> sleep.

> True, but that does not invalidate my comment, I meant to write that
> this is the only function that you *might* potentially want to call from
> interrupt context,

    Sure, I did want that. :-)

> and yet it does not trigger low-level I/O accesses to
> the underlying MDIO bus, but instead uses the PHY library state machine
> workqueue to do that.

    That's so.

> Thanks for the reminder though, that needs fixing ;)

    Hopefully it's fixable... I had to use GPIO interrupt for AVB_PHY_INT pin 
since I didn't want to create a thread just to call phy_mac_interrupt().

> --
> Florian

WBR, Sergei

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