Message-ID: <20130524170125.GX31290@titan.lakedaemon.net>
Date:	Fri, 24 May 2013 13:01:25 -0400
From:	Jason Cooper <jason@...edaemon.net>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Andrew Lunn <andrew@...n.ch>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	"linuxppc-dev@...ts.ozlabs.org list" <linuxppc-dev@...ts.ozlabs.org>,
	David Miller <davem@...emloft.net>,
	Lennert Buytenhek <buytenh@...tstofly.org>
Subject: Re: [PATCH 2/2] net: mv643xx_eth: proper initialization for
 Kirkwood SoCs

On Fri, May 24, 2013 at 01:03:25PM +0200, Linus Walleij wrote:
> On Fri, May 24, 2013 at 12:40 AM, Sebastian Hesselbarth
> <sebastian.hesselbarth@...il.com> wrote:
> > On 05/23/2013 08:40 PM, Jason Cooper wrote:
> 
> >> I think marvell,psc1_reset =<>; gives us the most flexibility in
> >> accurately describing the hardware.
> >
> >
> > IMHO using that is just another workaround for a broken driver. We
> > could hack the whole register setup in DT as it would still accurately
> > describe HW. Don't get me wrong, but I don't like it.
> >
> > Haven't checked how happy Linus Walleij is about pinctrl drivers with
> > reg values hacked in lately.
> 
> One of the things I've been ranting about lately is that Linux
> subsystem maintainers have become de-facto device tree
> standard commite chairs. :-(

This is the first I've heard this rant.  :(

To that end, I agree with you.  My frustration boiled down to trying to
predict the future, which is futile. :-P

For our scenario, once we can confirm our least popular kirkwood
variant, the 6282, behaves the same as we've seen so far, then
"marvell,kirkwood-eth" is fine by me.

> So to the actual question:
> 
> In general I think we need to draw a line and define what we
> mean with "describing the hardware" in a device tree.
> 
> We have some consensus:
> - <reg> properties to describe regsiter BASE offset in physical
>   memory and size.
> - Resources like IRQ, DMA channel, regulator, GPIO pin control
>   handles, are passed using <&ampersand> notation.
> 
> And so it goes on.
> 
> When it comes to defining different registers and their individual
> bits and the meaning of these and/or default values, I personally
> think that is making things harder for developers rather than
> simplifying things. I know that pinctrl-single is anyway doing this
> and I was talked into accepting it under circumstances where
> developers are being passed opaque machine-generated
> data that would otherwise be translated into unreadable header
> files littering the kernel.
> 
> For a coder it is definately better if the *driver* know these
> details, but whether that is possible seems to depend on things
> like hardware development process.

Agree.

> IMO: if you want to go down that road, what you really want is not
> ever more expressible device trees, but real open firmware,
> or ACPI or UEFI that can interpret and run bytecode as some
> "bios" for you. With DT coming from OF maybe this is a natural
> progression of things, but one has to realize when we reach the
> point where what we really want is a bios. Then your time is
> likely better spent with Tianocore or something than with the
> kernel.

shudder.  I like embedded systems because the *don't* have a bios.

thx,

Jason.
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