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

[Marc C]

Hi Mark,

>> 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

In a perfect world, the hardware designers would place _all_ of the registers needed to
support rebooting in a contiguous section of the memory map. However, this isn't the case
on some platforms, especially on ARM-based SoCs.

While I completely agree with you that the bindings describe hardware, I don't see how
Feng's work is contrary to that. Feng is working on logically-grouping an otherwise
"random" set of registers into a logical grouping. In this case, Feng is uniting a group
of registers and calling them the "reboot" register block.

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

>From what I understand, the arm-soc maintainers want to reduce (and perhaps even
eliminate) these board-specific constructs, and try to utilize common driver-code that
resides in the "driver" folder. I can vouch for the syscon/regmap framework as something
which would enable the effort.

Thanks,
Marc C

On 01/24/2014 10:23 AM, Mark Rutland wrote:
> 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 at arm.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 at apm.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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