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

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Message-ID: <20160514195016.GC26220@lunn.ch>
Date:	Sat, 14 May 2016 21:50:16 +0200
From:	Andrew Lunn <andrew@...n.ch>
To:	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>
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

On Sat, May 14, 2016 at 10:36:38PM +0300, Sergei Shtylyov wrote:
> 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 think we miss understood each other somewhere.

Your code is great for one gpio reset line for one phy.

I think there could be similar code one layer above to handle one gpio
line for multiple phys.

     Andrew