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

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Date:	Tue, 23 Jul 2013 22:20:53 +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 15:36:00 Alan Stern wrote:
> On Tue, 23 Jul 2013, Tomasz Figa wrote:
> > IMHO it would be better if you provided some code example, but let's
> > try to check if I understood you correctly.
> > 
> > 8><-------------------------------------------------------------------
> > -----
> > 
> > [Board file]
> > 
> > static struct phy my_phy;
> > 
> > static struct platform_device phy_pdev = {
> > 
> > 	/* ... */
> > 	.platform_data = &my_phy;
> > 	/* ... */
> > 
> > };
> > 
> > static struct platform_device phy_pdev = {
> 
> This should be controller_pdev, not phy_pdev, yes?

Right. A copy-pasto.

> 
> > 	/* ... */
> > 	.platform_data = &my_phy;
> > 	/* ... */
> > 
> > };
> > 
> > [Provider driver]
> > 
> > struct phy *phy = pdev->dev.platform_data;
> > 
> > ret = phy_create(phy);
> > 
> > [Consumer driver]
> > 
> > struct phy *phy = pdev->dev.platform_data;
> > 
> > ret = phy_get(&pdev->dev, phy);
> 
> Or even just phy_get(&pdev->dev), because phy_get() could be smart
> enough to to set phy = dev->platform_data.

Unless you need more than one PHY in this driver...

> 
> > ----------------------------------------------------------------------
> > --><8
> > 
> > Is this what you mean?
> 
> That's what I was going to suggest too.  The struct phy is defined in
> the board file, which already knows about all the PHYs that exist in
> the system.  (Or perhaps it is allocated dynamically, so that when many
> board files are present in the same kernel, only the entries listed in
> the board file for the current system get created.) 

Well, such dynamic allocation is a must. We don't accept non-multiplatform 
aware code anymore, not even saying about multiboard.

> Then the
> structure's address is stored in the platform data and made available
> to both the provider and the consumer.

Yes, technically this can work. You would still have to perform some kind 
of synchronization to make sure that the PHY bound to this structure is 
actually present. This is again technically doable (e.g. a list of 
registered struct phys inside PHY core).

> Even though the struct phy is defined (or allocated) in the board file,
> its contents don't get filled in until the PHY driver provides the
> details.

You can't assure this. Board file is free to do whatever it wants with 
this struct. A clean solution would prevent this.

> > It's technically correct, but quality of this solution isn't really
> > nice, because it's a layering violation (at least if I understood
> > what you mean). This is because you need to have full definition of
> > struct phy in board file and a structure that is used as private data
> > in PHY core comes from platform code.
> 
> You don't have to have a full definition in the board file.  Just a
> partial definition -- most of the contents can be filled in later, when
> the PHY driver is ready to store the private data.
> 
> It's not a layering violation for one region of the kernel to store
> private data in a structure defined by another part of the kernel.
> This happens all the time (e.g., dev_set_drvdata).

Not really. The phy struct is something that _is_ private data of PHY 
subsystem, not something that can store private data of PHY subsystem 
(sure it can store private data of particular PHY driver, but that's 
another story) and only PHY subsystem should have access to its contents.

By the way, we need to consider other cases here as well, for example it 
would be nice to have a single phy_get() function that works for both non-
DT and DT cases to make the consumer driver not have to worry whether it's 
being probed from DT or not.

I'd suggest simply reusing the lookup method of regulator framework, just 
as I suggested here:

http://thread.gmane.org/gmane.linux.ports.arm.kernel/252813/focus=101661

Best regards,
Tomasz

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