linux-kernel - Re: [PATCH 01/15] drivers: phy: add generic PHY framework

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Date:	Tue, 23 Jul 2013 23:31:31 +0200
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Tomasz Figa <t.figa@...sung.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Kishon Vijay Abraham I <kishon@...com>,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	broonie@...nel.org,
	Sylwester Nawrocki <sylvester.nawrocki@...il.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	kyungmin.park@...sung.com, balbi@...com, jg1.han@...sung.com,
	s.nawrocki@...sung.com, kgene.kim@...sung.com,
	grant.likely@...aro.org, tony@...mide.com, arnd@...db.de,
	swarren@...dia.com, devicetree@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org, linux-omap@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-media@...r.kernel.org,
	linux-fbdev@...r.kernel.org, akpm@...ux-foundation.org,
	balajitk@...com, george.cherian@...com, nsekhar@...com,
	olof@...om.net, Stephen Warren <swarren@...dotorg.org>,
	b.zolnierkie@...sung.com,
	Daniel Lezcano <daniel.lezcano@...aro.org>
Subject: Re: [PATCH 01/15] drivers: phy: add generic PHY framework

On Tuesday 23 of July 2013 17:14:20 Alan Stern wrote:
> On Tue, 23 Jul 2013, Tomasz Figa wrote:
> > > If you want to keep the phy struct completely separate from the
> > > board
> > > file, there's an easy way to do it.  Let's say the board file knows
> > > about N different PHYs in the system.  Then you define an array of N
> > > pointers to phys:
> > > 
> > > struct phy *(phy_address[N]);
> > > 
> > > In the platform data for both PHY j and its controller, store
> > > 
> > > &phy_address[j].  The PHY provider passes this cookie to phy_create:
> > > 	cookie = pdev->dev.platform_data;
> > > 	ret = phy_create(phy, cookie);
> > > 
> > > and phy_create simply stores: *cookie = phy.  The PHY consumer does
> > > 
> > > much the same the same thing:
> > > 	cookie = pdev->dev.platform_data;
> > > 	phy = phy_get(cookie);
> > > 
> > > phy_get returns *cookie if it isn't NULL, or an ERR_PTR otherwise.
> > 
> > OK, this can work. Again, just technically, because it's rather ugly.
> 
> There's no reason the phy_address things have to be arrays.  A separate
> individual pointer for each PHY would work just as well.
> 
> > Where would you want to have those phy_address arrays stored? There
> > are no board files when booting with DT. Not even saying that you
> > don't need to use any hacky schemes like this when you have DT that
> > nicely specifies relations between devices.
> 
> If everybody agrees DT has a nice scheme for specifying relations
> between devices, why not use that same scheme in the PHY core?

It is already used, for cases when consumer device has a DT node attached. 
In non-DT case this kind lookup translates loosely to something that is 
being done in regulator framework - you can't bind devices by pointers, 
because you don't have those pointers, so you need to use device names.

> > Anyway, board file should not be considered as a method to exchange
> > data between drivers. It should be used only to pass data from it to
> > drivers, not the other way. Ideally all data in a board file should
> > be marked as const and __init and dropped after system
> > initialization.
> 
> The phy_address things don't have to be defined or allocated in the
> board file; they could be set up along with the platform data.

There is no platform data when booting with DT.

> In any case, this was simply meant to be a suggestion to show that it
> is relatively easy to do what you need without using name or ID
> strings.

Sure. It's good to have different options discussed as well.

Best regards,
Tomasz

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