Message-ID: <55534A5D.6050904@linaro.org>
Date:	Wed, 13 May 2015 13:58:05 +0100
From:	Daniel Thompson <daniel.thompson@...aro.org>
To:	Maxime Coquelin <mcoquelin.stm32@...il.com>,
	Arnd Bergmann <arnd@...db.de>
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Subject: Re: [PATCH v8 14/16] ARM: dts: Introduce STM32F429 MCU

On 13/05/15 12:45, Maxime Coquelin wrote:
> 2015-05-12 23:21 GMT+02:00 Arnd Bergmann <arnd@...db.de>:
>> On Saturday 09 May 2015 09:53:56 Maxime Coquelin wrote:
>>> +#include  <dt-bindings/mfd/stm32f4-rcc.h>
>>> +
>>>
>>
>> Can you find a way to avoid this dependency?
>>
>> Maybe you can change the bindings so that the numbers you pass as
>> arguments to the reset and clock specifiers reflect the numbers that
>> the hardware use?
>
> If I understand correctly, you prefer the way I did in v7 [0]?
>
> I don't have a strong opinion on this. Either way is fine to me.
>
> I changed the bindings in the v8 after discussions with Daniel
> Thompson, who is implementing the clock driver part of the RCC IP.
>
> He proposed we used common defines, because each peripheral has a
> reset line and a clock gate.
> Both reset and clock are represented as a single bit, with only the
> base offset differing between clock and reset.
> You can have a look at chapter 6 of the reference manual [1] if you
> find some time.
>
> Having common defines between clocks and reset make sense to me, but I
> also understand your point of avoiding dependencies.
>
> Maybe I can revert back to v7 bindings for now, and then we can
> reconsider using common defines when Daniel will send the clock
> patches.
> Note that doing that won't break the DT binary compatibility, as the
> raw reset values, or the ones from defines are the same.
>
> Daniel, could you share an example of the bindings you would use for the clocks?

For the most cases, where there is a clock gate just before the 
peripheral it looks pretty much like the reset driver and I use the bit 
offset of the clock gating bit as the index.

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.

2. Ungated dividers. For these I am using the bit offset of the LSB of
    the mux field.

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";
		};


Daniel.


> Kind regards,
> Maxime
>
>>
>>          Arnd
>
> [0]: http://lkml.iu.edu/hypermail/linux/kernel/1504.3/04523.html
> [1]: http://www.st.com/web/en/resource/technical/document/reference_manual/DM00031020.pdf
>

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