linux-kernel - Re: [PATCH 09/33] ARM: ux500: Supply the I2C clocks lookup to the DBX500 DT

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Message-ID: <20130827080635.GC6152@lee--X1>
Date:	Tue, 27 Aug 2013 09:06:35 +0100
From:	Lee Jones <lee.jones@...aro.org>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Sascha Hauer <s.hauer@...gutronix.de>,
	Linus Walleij <linus.walleij@...aro.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 09/33] ARM: ux500: Supply the I2C clocks lookup to the
 DBX500 DT

On Fri, 23 Aug 2013, Mark Rutland wrote:

> On Fri, Aug 23, 2013 at 08:56:07AM +0100, Lee Jones wrote:
> > I had a short chat with Rob last night about this. I'm going to loop
> > him in to the conversation, as he wrote the binding.
> > 
> > > > When most of the other clocks that we deal with are being requested,
> > > > they rely on being index zero:
> > > > 
> > > >   drivers/i2c/busses/i2c-nomadik.c: dev->clk = clk_get(&adev->dev, NULL);
> > > 
> > > Look at drivers/clk/clkdev.c, there's some fuzzy matching
> > > involved when you pass NULL as connection id.
> > 
> > Yes, I've been looking at that. This is why it works currently. I
> > think I need to change all of the drivers to specify which clock they
> > want. At the moment that 'fuzzy matching' is what's saving us. If
> > anyone were to change our DTS file to match what the binding says,
> > then it would cease to work. I'm guessing this is the same for all
> > other DTS files too:
> 
> I think if anything, the binding document(s) should be updated to
> describe that apb_pclk is referred to by name, and the names of the
> other clocks should be described in the specific device bindings. We can
> then modify the drivers which grab clock 0 to explicitly grab the first
> clock by name, and backwards compatibility should not be broken.
> 
> I don't believe any other OS has implemented the common clock bindings,
> and we've never supported the binding as described. Let's correct the
> de-facto standard into a standard by decree.

I think we need to respect, or at least take into consideration the
reason for the original 'de-facto' standard. Other OSes shouldn't be
forced to provide a named clock request in order to obtain
'apb_pclk'. If the binding says it should be first, then perhaps we
should do just that. It's simply a matter of naming all subsequent
clocks related to AMBA devices.

-- 
Lee Jones
Linaro ST-Ericsson Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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