linux-kernel - Re: [RFCv2 1/3] docs: dts: Added documentation for Xilinx Zynq Reset Controller bindings.

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Message-ID: <CAAtXAHd8kG_FtKTW-2T2KToXesWgsgxkZ3vpXZ_oRjGCSfpFgw@mail.gmail.com>
Date:	Tue, 28 Jul 2015 23:14:58 -0700
From:	Moritz Fischer <moritz.fischer@...us.com>
To:	Sören Brinkmann <soren.brinkmann@...inx.com>
Cc:	Philipp Zabel <p.zabel@...gutronix.de>, robh+dt@...nel.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, Kumar Gala <galak@...eaurora.org>,
	Michal Simek <michal.simek@...inx.com>, linux@....linux.org.uk,
	devicetree@...r.kernel.org,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFCv2 1/3] docs: dts: Added documentation for Xilinx Zynq Reset
 Controller bindings.

Hi Sören,

On Tue, Jul 28, 2015 at 3:53 PM, Sören Brinkmann
<soren.brinkmann@...inx.com> wrote:
> On Mon, 2015-07-27 at 09:52PM -0700, Moritz Fischer wrote:
>> Hi Sören,
>>
>> thanks for your feedback.
>>
>> On Mon, Jul 27, 2015 at 7:58 PM, Sören Brinkmann
>> <soren.brinkmann@...inx.com> wrote:
>> > Hi Moritz,
>> >
>> > On Fri, 2015-07-24 at 05:21PM -0700, Moritz Fischer wrote:
>> >> Signed-off-by: Moritz Fischer <moritz.fischer@...us.com>
>> >> ---
>> >>  Documentation/devicetree/bindings/reset/zynq-reset-pl.txt | 13 +++++++++++++
>> >>  1 file changed, 13 insertions(+)
>> >>  create mode 100644 Documentation/devicetree/bindings/reset/zynq-reset-pl.txt
>> >>
>> >> diff --git a/Documentation/devicetree/bindings/reset/zynq-reset-pl.txt b/Documentation/devicetree/bindings/reset/zynq-reset-pl.txt
>> >> new file mode 100644
>> >> index 0000000..ac4499e
>> >> --- /dev/null
>> >> +++ b/Documentation/devicetree/bindings/reset/zynq-reset-pl.txt
>> >> @@ -0,0 +1,13 @@
>> >> +Xilinx Zynq PL Reset Manager
>> >> +
>> >> +Required properties:
>> >> +- compatible: "xlnx,zynq-reset-pl"
>> >> +- syscon <&slcr>;
>> >> +- #reset-cells: 1
>> >> +
>> >> +Example:
>> >> +     rstc: rstc@240 {
>> >> +             #reset-cells = <1>;
>> >> +             compatible = "xlnx,zynq-reset-pl";
>> >> +             syscon = <&slcr>;
>> >> +     };
>> >
>> > I think you also have to add the outputs and make them part of the
>> > binding. Otherwise you'd have to read the implementation to find
>> > out what device should be hooked up to which output of the reset-controller.
>>
>> Is something like this what you had in mind? I had that prepared for
>> the next round of patches:
>>
>> Reset outputs:
>>  0  : soft reset
>>  32 : ddr reset
>>  64 : topsw reset
>>  96 : dmac reset
>>  128: usb0 reset
>>  129: usb1 reset
>>  160: gem0 reset
>>  161: gem1 reset
>>  164: gem0 rx reset
>>  165: gem1 rx reset
>>  166: gem0 ref reset
>>  167: gem1 ref reset
>>  192: sdio0 reset
>>  193: sdio1 reset
>>  196: sdio0 ref reset
>>  197: sdio1 ref reset
>>  224: spi0 reset
>>  225: spi1 reset
>>  226: spi0 ref reset
>>  227: spi1 ref reset
>>  256: can0 reset
>>  257: can1 reset
>>  258: can0 ref reset
>>  259: can1 ref reset
>>  288: i2c0 reset
>>  289: i2c1 reset
>>  320: uart0 reset
>>  321: uart1 reset
>>  322: uart0 ref reset
>>  323: uart1 ref reset
>>  352: gpio reset
>>  384: lqspi reset
>>  385: qspi ref reset
>>  416: smc reset
>>  417: smc ref reset
>>  448: ocm reset
>>  512: fpga0 out reset
>>  513: fpga1 out reset
>>  514: fpga2 out reset
>>  515: fpga3 out reset
>>  544: a9 reset 0
>>  545: a9 reset 1
>>  552: peri reset
>
> Basically, yes. I guess the gaps are due to directly mapping this number
> to bank and bit instead of doing some more complex mapping in between?
> I'm not sure whether I like this :) I guess if a number is off the
> driver would still toggle the addressed bit?

My assumption was that people would use a #include
<dt-bindings/xlnx,zynq-reset.h> in their dts. Assuming I got the
numbers in there right this makes it hard to misuse by accident.
I'm not saying it's perfect ...

> I'm not sure, is it worth
> to do some explicit mapping from logical outputs to a physical reset? It
> seems it would be a little safer since it would be easy to check that
> the addressed reset is valid and there wouldn't be any reserved/invalid
> bits be toggled. Also, it would make the outputs in here a continuous
> series of numbers without these gaps. Not sure though whether
> it's worth the additional complexity in the implementation.

So your suggestion is to have a large switch case kind of thingy? I
thought about it and it seemed complex as there's quite a bunch of
resets with gaps. Do you know of a driver that does something similar?
When I wrote this I looked at the other reset drivers and figured they
all had this kind of bank mapping of sorts so I assumed that's how
people usually do it.

>
>         Thanks,
>         Sören

Thanks again for your input,

Moritz
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