linux-kernel - Re: [PATCH RFT 1/2] phylib: add device reset GPIO support

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Message-ID: <cc232c9e-ef25-482d-0978-cbdfe03bad22@cogentembedded.com>
Date:	Sat, 14 May 2016 22:36:38 +0300
From:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
To:	Andrew Lunn <andrew@...n.ch>
Cc:	Roger Quadros <rogerq@...com>,
	Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
	grant.likely@...aro.org, robh+dt@...nel.org,
	devicetree@...r.kernel.org, f.fainelli@...il.com,
	netdev@...r.kernel.org, frowand.list@...il.com, pawel.moll@....com,
	mark.rutland@....com, ijc+devicetree@...lion.org.uk,
	galak@...eaurora.org, linux-kernel@...r.kernel.org,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH RFT 1/2] phylib: add device reset GPIO support

Hello.

On 05/14/2016 02:44 AM, Andrew Lunn wrote:

>>>>> Another issue is that on some boards we have one reset line tied to
>>>>> multiple PHYs.How do we prevent multiple resets being taking place when each of
>>>>> the PHYs are registered?
>>>>
>>>>   My patch just doesn't address this case -- it's about the
>>>> individual resets only.
>>>
>>> This actually needs to be addresses a layer above. What you have is a
>>> bus reset, not a device reset.
>>
>>    No.
>>    There's simply no such thing as a bus reset for the xMII/MDIO
>> busses, there's simply no reset signaling on them. Every device has
>> its own reset signal and its own timing requirements.
>
> Except in the case above, where two phys are sharing the same reset
> signal. So although it is not part of the mdio standard to have a bus
> reset, this is in effect what the gpio line is doing, resetting all
> devices on the bus. If you don't model that as a bus reset, how do you
> model it?

    I'm not suggesting that the shared reset should be handled by my patch. 
Contrariwise, I suggested to use the mii_bus::reset() method -- I see it as a 
necessary evil. However, in the more common case of a single PHY, this method 
simply doesn't scale -- you'd have to teach each and every individual MAC/ 
MDIO driver to do the GPIO reset trick.

>       Andrew

MBR, Sergei