linux-kernel - Re: [PATCH v3 1/8] rsb: Add generic Reduced Serial Bus (RSB) controller binding documentation

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Date:	Thu, 20 Aug 2015 23:58:39 +0800
From:	Chen-Yu Tsai <wens@...e.org>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mark Brown <broonie@...nel.org>,
	devicetree <devicetree@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-sunxi <linux-sunxi@...glegroups.com>,
	Hans de Goede <hdegoede@...hat.com>,
	Meng Zhang <kevin@...winnertech.com>,
	Shuge <shuge@...winnertech.com>,
	Meng Zhang <kevin.z.m.zh@...il.com>
Subject: Re: [PATCH v3 1/8] rsb: Add generic Reduced Serial Bus (RSB)
 controller binding documentation

On Thu, Aug 20, 2015 at 11:08 PM, Maxime Ripard
<maxime.ripard@...e-electrons.com> wrote:
> Hi,
>
> Thanks a lot for working on this.
>
> On Wed, Aug 19, 2015 at 12:20:02PM +0800, Chen-Yu Tsai wrote:
>> Reduced Serial Bus is a proprietary 2-line push-pull serial bus
>> supporting multiple slave devices.
>>
>> It was developed by Allwinner, Inc. and used by Allwinner and X-Powers,
>> Inc. for their line of PMICs and other peripheral ICs.
>>
>> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
>> ---
>>  Documentation/devicetree/bindings/rsb/rsb.txt | 50 +++++++++++++++++++++++++++
>>  1 file changed, 50 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/rsb/rsb.txt
>>
>> diff --git a/Documentation/devicetree/bindings/rsb/rsb.txt b/Documentation/devicetree/bindings/rsb/rsb.txt
>> new file mode 100644
>> index 000000000000..0b027948ca9c
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/rsb/rsb.txt
>> @@ -0,0 +1,50 @@
>> +Reduced Serial Bus (RSB) Controller
>> +
>> +This document defines a generic set of bindings for use by RSB controllers.
>> +A controller is modelled in device tree as a node with zero or more child
>> +nodes, each representing a unique slave device on the bus.
>> +
>> +Required properties:
>> +
>> + - #address-cells : must be 2
>> + - #size-cells : must be 0
>> +
>> +Optional properties:
>> +
>> + - clock-frequency : Desired bus clock frequency in Hz. Maximum is 20 MHz.
>
> What is the default if not set?

Presently the driver would have it default to 1 MHz, Which doesn't match
the driver binding. Will fix this.

>> +
>> +Child nodes:
>> +
>> +An RSB controller node can contain zero or more child nodes representing
>> +slave devices on the bus.  Child 'reg' properties are specified as a
>> +runtime address, hardware address pair. The hardware address is hardwired
>> +in the device, which can normally be found in the datasheet. The runtime
>> +address is set by software. No 2 devices on the same bus shall have the
>> +same runtime address.
>> +
>> +Valid runtime addresses - There are only 15 valid runtime addresses:
>> +
>> +    0x17, 0x2d, 0x3a, 0x4e, 0x59, 0x63, 0x74, 0x8b,
>> +    0x9c, 0xa6, 0xb1, 0xc5, 0xd2, 0xe8, 0xff
>> +
>> +It is highly recommended that one choose the same runtime addresses as
>> +vendor BSPs use so that a) the addresses remain the same across different
>> +software systems, and b) addresses of supported and listed slave devices
>> +don't conflict with unsupported or not yet listed devices.
>
> I'd expect to have the hardware address first, but maybe it's just me
> :)

I don't know. It's only used at init time.

And in my latest experience, once the runtime address is set by the
bootloader, it can't be changed. My earlier experience was the opposite,
though I haven't figured out why.

>
>> +Example:
>> +
>> +     rsb@... {
>> +             compatible = "...";
>> +             reg = <...>;
>> +             /* ... */
>> +             #address-cells = <2>;
>> +             #size-cells = <0>;
>> +
>> +             pmic@2d {
>
> The unit-address should be 2d,3e3.

Hmm... I didn't know this was legal.

>> +                     compatible = "...";
>> +                     reg = <0x2d 0x3e3>;
>> +
>> +                     /* ... */
>> +             };
>> +     };
>> --
>> 2.5.0
>>
>
> --
> Maxime Ripard, Free Electrons
> Embedded Linux, Kernel and Android engineering
> http://free-electrons.com
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