linux-kernel - Re: [PATCH V4 5/5] Documentation: power: reset: Add documentation for generic SYSCON reboot driver

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Message-ID: <20140124182355.GF4758@e106331-lin.cambridge.arm.com>
Date:	Fri, 24 Jan 2014 18:23:55 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Feng Kan <fkan@....com>
Cc:	"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>
Subject: Re: [PATCH V4 5/5] Documentation: power: reset: Add documentation
 for generic SYSCON reboot driver

On Fri, Jan 24, 2014 at 06:03:10PM +0000, Feng Kan wrote:
> On Fri, Jan 24, 2014 at 3:39 AM, Mark Rutland <mark.rutland@....com> wrote:
> > On Thu, Jan 23, 2014 at 07:20:01PM +0000, Feng Kan wrote:
> >> Add documentation for generic SYSCON reboot driver.
> >>
> >> Signed-off-by: Feng Kan <fkan@....com>
> >> ---
> >>  .../bindings/power/reset/syscon-reboot.txt         |   16 ++++++++++++++++
> >>  1 files changed, 16 insertions(+), 0 deletions(-)
> >>  create mode 100644 Documentation/devicetree/bindings/power/reset/syscon-reboot.txt
> >>
> >> diff --git a/Documentation/devicetree/bindings/power/reset/syscon-reboot.txt b/Documentation/devicetree/bindings/power/reset/syscon-reboot.txt
> >> new file mode 100644
> >> index 0000000..e9eb1fe
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/power/reset/syscon-reboot.txt
> >> @@ -0,0 +1,16 @@
> >> +Generic SYSCON mapped register reset driver
> >
> > Bindings should describe hardware, not drivers.
> >
> > What precisely does this binding describe?
> >
> >> +
> >> +Required properties:
> >> +- compatible: should contain "syscon-reboot"
> >> +- regmap: this is phandle to the register map node
> >> +- offset: offset in the register map for the reboot register
> >> +- mask: the reset value written to the reboot register
> >> +
> >> +Examples:
> >> +
> >> +reboot {
> >> +   compatible = "syscon-reboot";
> >> +   regmap = <&regmapnode>;
> >> +   offset = <0x0>;
> >> +   mask = <0x1>;
> >> +};
> >
> > Access size? Endianness?
> FKAN: are you asking for documentation? I don't see alot of example of
> support for these.

If I used the enippet in the example, what endianness and access size
should I expect an OS to perform? That should be documented.

If this doesn't match the general case, we can add properties later to
adjust the access size and/or endianness. We just need to document what
the binding actually describes currently, or it's not possible to
implement anything based off of the binding documentation.

I should be able to read a binding document and write a dts. I shouldn't
have to read the code to figure out what the binding describes.

> 
> >
> > Why can we not have a binding for the register bank this exists in, and
> > have that pass on the appropriate details to a syscon-reboot driver?
> 
> FKAN: Thats a good idea. But the hardware in this case (SCU) system
> clock unit has a bunch of registers used for different functions. If syscon is
> used alot in this case and we pile more attribute into it. It would get kinda
> messy after a while.

Huh?

What's wrong with having a system clock unit binding, that the kernel
can decompose as appropriate?

I don't get your syscon argument.

Thanks,
Mark.
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