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Message-ID: <11310179.epfRucfQKB@wuerfel>
Date:	Wed, 13 May 2015 17:28:57 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Daniel Thompson <daniel.thompson@...aro.org>
Cc:	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Andreas Färber <afaerber@...e.de>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Rob Herring <robh+dt@...nel.org>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	Linus Walleij <linus.walleij@...aro.org>,
	Stefan Agner <stefan@...er.ch>,
	Peter Meerwald <pmeerw@...erw.net>,
	Paul Bolle <pebolle@...cali.nl>,
	Peter Hurley <peter@...leysoftware.com>,
	Andy Shevchenko <andy.shevchenko@...il.com>,
	Chanwoo Choi <cw00.choi@...sung.com>,
	Russell King <linux@....linux.org.uk>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Joe Perches <joe@...ches.com>,
	Vladimir Zapolskiy <vladimir_zapolskiy@...tor.com>,
	Lee Jones <lee.jones@...aro.org>,
	Jonathan Corbet <corbet@....net>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Slaby <jslaby@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"David S. Miller" <davem@...emloft.net>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Antti Palosaari <crope@....fi>, Tejun Heo <tj@...nel.org>,
	Will Deacon <will.deacon@....com>,
	Nikolay Borisov <Nikolay.Borisov@....com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Kees Cook <keescook@...omium.org>,
	Michal Marek <mmarek@...e.cz>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	Linux-Arch <linux-arch@...r.kernel.org>,
	"linux-api@...r.kernel.org" <linux-api@...r.kernel.org>,
	Nicolae Rosia <nicolae.rosia@...il.com>,
	Kamil Lulko <rev13@...pl>
Subject: Re: [PATCH v8 14/16] ARM: dts: Introduce STM32F429 MCU

On Wednesday 13 May 2015 16:20:34 Daniel Thompson wrote:
> For the all reset bits:
> 
>    clock idx = reset idx + 256
> 
> The opposite is not true; the clock bits are a superset of the reset 
> bits (the reset bits act on cells but some cells have >1 clock).

Ok, in that case, I would strongly recommend subtracting that 256
offset keeping the numbers the same, to remove the function-type
macros.

> >> However there are a couple of clocks without gating just before the
> >> clock reaches the peripheral:
> >>
> >> 1. A hard coded /8. I think this will have to be given a synthetic
> >>      number.
> >
> > If this is just a divider, why not use a separate DT node for that,
> > like this:
> >
> >          clock {
> >                  compatible = "fixed-factor-clock";
> >                  clocks = <&parentclk>;
> >                  #clock-cells = <0>;
> >                  clock-div = <8>;
> >                  clock-mult = <1>;
> >          };
> >
> > No need to assign a number for this.
> 
> I'd wondered about doing that.
> 
> It will certainly work but it seemed a bit odd to me to have one (really 
> tiny) part of the RCC cell included seperately in the platform 
> description whilst all the complicated bits end up aggregated into the 
> RCC cell.
> 
> Is there much prior art that uses this type of trick to avoid having 
> magic numbers into the bindings?

Are you sure that divider is actually part of the RCC?

> >> 2. Ungated dividers. For these I am using the bit offset of the LSB of
> >>      the mux field.
> >
> > Do these ones also come with resets?
> 
> No. They mostly run to the core and its intimate peripherals (i.e. only 
> reset line comes from WDT).

Ok.

> >> So I think there is only one value that is completely unrelated to the
> >> hardware and will use a magic constant instead.
> >>
> >> I had planned to macros similar to the STM32F4_AxB_RESET() family of
> >> macros in both clk driver and DT in order to reuse the bit layouts from
> >> dt-bindings/mfd/stm32f4-rcc.h .
> >>
> >> Normal case would have looked like this:
> >>
> >>                  timer3: timer@...00000 {
> >>                          compatible = "st,stm32-timer";
> >>                          reg = <0x40000000 0x400>;
> >>                          interrupts = <28>;
> >>                          resets = <&rcc STM32F4_APB1_RESET(TIM3)>;
> >>                          clocks = <&rcc STM32F4_APB1_CLK(TIM3)>;
> >>                          status = "disabled";
> >>                  };
> >>
> >> Without the macros it looks like this:
> >>
> >>                  timer3: timer@...00000 {
> >>                          compatible = "st,stm32-timer";
> >>                          reg = <0x40000000 0x400>;
> >>                          interrupts = <28>;
> >>                          resets = <&rcc 257>;
> >>                          clocks = <&rcc 513>;
> >>                          status = "disabled";
> >>                  };
> >>
> >> However we could perhaps be more literate even if we don't use the macros?
> >>
> >>                  timer3: timer@...00000 {
> >>                          compatible = "st,stm32-timer";
> >>                          reg = <0x40000000 0x400>;
> >>                          interrupts = <28>;
> >>                          resets = <&rcc ((0x20*8) + 1)>;
> >>                          clocks = <&rcc ((0x40*8) + 1)>;
> >>                          status = "disabled";
> >>                  };
> >
> > How about #address-cells = <2>, so you can do
> >
> > 		resets = <&rcc 8 1>;
> > 		clocks = <&rcc 8 1>;
> >
> > with the first cell being an index for the block and the second cell the
> > bit number within that block.
> 
> That would suit me very well (although is the 0x20/0x40 not the 8 that 
> we would need in the middle column).

We don't normally use register offsets in DT. The number 8 here instead
would indicate block 8, where each block is four bytes wide. Using the
same index here for reset and clock would also help readability.

	Arnd
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