Date:	Tue, 23 Jul 2013 22:46:53 +0200
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Greg KH <gregkh@...uxfoundation.org>
Cc:	Tomasz Figa <t.figa@...sung.com>,
	Stephen Warren <swarren@...dotorg.org>,
	Kishon Vijay Abraham I <kishon@...com>,
	Alan Stern <stern@...land.harvard.edu>,
	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, 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 11:04:14 Greg KH wrote:
> On Tue, Jul 23, 2013 at 07:48:11PM +0200, Tomasz Figa wrote:
> > On Tuesday 23 of July 2013 10:37:11 Greg KH wrote:
> > > On Tue, Jul 23, 2013 at 06:50:29PM +0200, Tomasz Figa wrote:
> > > > > Ick, no.  Why can't you just pass the pointer to the phy itself?
> > > > >  If
> > > > > you
> > > > > had a "priv" pointer to search from, then you could have just
> > > > > passed
> > > > > the
> > > > > original phy pointer in the first place, right?
> > > > 
> > > > IMHO it would be better if you provided some code example, but
> > > > let's
> > > > try to check if I understood you correctly.
> > > 
> > > It's not my code that I want to have added, so I don't have to write
> > > examples, I just get to complain about the existing stuff :)
> > 
> > Still, I think that some small code snippets illustrating the idea are
> > really helpful.
> > 
> > > > 8><---------------------------------------------------------------
> > > > -----
> > > > ----
> > > > 
> > > > [Board file]
> > > > 
> > > > static struct phy my_phy;
> > > > 
> > > > static struct platform_device phy_pdev = {
> > > > 
> > > > 	/* ... */
> > > > 	.platform_data = &my_phy;
> > > > 	/* ... */
> > > > 
> > > > };
> > > > 
> > > > static struct platform_device phy_pdev = {
> > > > 
> > > > 	/* ... */
> > > > 	.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);
> > > > 
> > > > ------------------------------------------------------------------
> > > > -----
> > > > -><8
> > > > 
> > > > Is this what you mean?
> > > 
> > > No.  Well, kind of.  What's wrong with using the platform data
> > > structure unique to the board to have the pointer?
> > > 
> > > For example (just randomly picking one), the ata-pxa driver would
> > > change include/linux/platform_data/ata-pxa.h to have a phy pointer
> > > in it:
> > > 
> > > struct phy;
> > > 
> > > struct  pata_pxa_pdata {
> > > 
> > > 	/* PXA DMA DREQ<0:2> pin */
> > > 	uint32_t	dma_dreq;
> > > 	/* Register shift */
> > > 	uint32_t	reg_shift;
> > > 	/* IRQ flags */
> > > 	uint32_t	irq_flags;
> > > 	/* PHY */
> > > 	struct phy	*phy;
> > > 
> > > };
> > > 
> > > Then, when you create the platform, set the phy* pointer with a call
> > > to
> > > phy_create().  Then you can use that pointer wherever that plaform
> > > data
> > > is available (i.e. whereever platform_data is at).
> > 
> > Hmm? So, do you suggest to call phy_create() from board file? What
> > phy_ops struct and other hardware parameters would it take?
> > 
> > > > > The issue is that a string "name" is not going to scale at all,
> > > > > as it
> > > > > requires hard-coded information that will change over time (as
> > > > > the
> > > > > existing clock interface is already showing.)
> > > > 
> > > > I fully agree that a simple, single string will not scale even in
> > > > some,
> > > > not so uncommon cases, but there is already a lot of existing
> > > > lookup
> > > > solutions over the kernel and so there is no point in introducing
> > > > another one.
> > > 
> > > I'm trying to get _rid_ of lookup "solutions" and just use a real
> > > pointer, as you should.  I'll go tackle those other ones after this
> > > one
> > > is taken care of, to show how the others should be handled as well.
> > 
> > There was a reason for introducing lookup solutions. The reason was
> > that in board file there is no way to get a pointer to something that
> > is going to be created much later in time. We don't do time travel
> > ;-).
> > 
> > > > > Please just pass the real "phy" pointer around, that's what it
> > > > > is
> > > > > there
> > > > > for.  Your "board binding" logic/code should be able to handle
> > > > > this,
> > > > > as
> > > > > it somehow was going to do the same thing with a "name".
> > > > 
> > > > 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.
> > > 
> > > No, just a pointer, you don't need the "full" structure until you
> > > get to some .c code that actually manipulates the phy itself, for
> > > all other places, you are just dealing with a pointer and a
> > > structure you never reference.
> > > 
> > > Does that make more sense?
> > 
> > Well, to the point that I think I now understood your suggestion.
> > Unfortunately the suggestion alone isn't really something that can be
> > done, considering how driver core and generic frameworks work.
> 
> Ok, given that I seem to be totally confused as to exactly how the
> board-specific frameworks work, I'll take your word for it.

Well, they are working in a way that keeps separation of layers, making 
things clean. Platform code should not (well, there might exist some in 
tree hacks, but this should not be propagated) used to exchange data 
between drivers, but rather to specify board specific parameters for 
generic drivers. If drivers need to cooperate, there must be a dedicated 
interface for this, like the PHY framework Kishon is introducing here.

Sure, with platform code you can do a lot of hacky things, for example you 
can simply provide PHY callbacks inside platform_data, like it was being 
done historically, but that's just ugly.

Anyway, board files should now be rather considered a historical thing. We 
are moving towards full DT-based description on ARM systems and so board 
files and related things, like name-based lookups, statically registered 
platform devices and so one are going away. Device Tree handles such 
provider-consumer links automatically using specifiers with phandles and 
lookup by node + provider-specific specifier args, so all the problems 
with binding things together just go away.

> But again, I will not accept "lookup by name" type solutions, when the
> "name" is dynamic and will change.  Because you are using a "name", you
> can deal with a pointer, putting it _somewhere_ in your board-specific
> data structures, as you are going to need to store it anyway (hint, you
> had to get that "name" from somewhere, right?)

Yes. This kind of artificial names passed to both provider and consumer 
isn't really a good way of lookup. This is just an example of bad lookup 
key, though. IMHO for a good example of lookup you should see regulator 
framework.

> And maybe the way that these "generic frameworks" are created is wrong,
> given that you don't feel that a generic pointer can be passed to the
> needed devices.  That seems like a huge problem, one that has already
> been pointed out is causing issues with other subsystems.

What problem are you talking about here? AFAIK frameworks using correctly 
designed lookup do work fine for most, if not all, people. See the 
regulator framework.

> So maybe they need to be fixed?

I don't really think anything is broken here, so there is nothing to fix.

Best regards,
Tomasz

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