[resend v2: PATCH 1/2] dt-bindings: Document the hi3660 reset bindings

[Philipp Zabel]

Am Montag, den 05.12.2016, 17:40 -0600 schrieb Rob Herring:
> On Fri, Dec 02, 2016 at 03:10:13PM +0100, Philipp Zabel wrote:
> > Am Freitag, den 02.12.2016, 13:32 +0100 schrieb Arnd Bergmann:
> > > On Friday, December 2, 2016 8:21:33 AM CET zhangfei wrote:
> > > > Hi, Arnd
> > > > 
> > > > On 2016年12月01日 20:05, Arnd Bergmann wrote:
> > > > > On Thursday, December 1, 2016 8:48:40 AM CET Zhangfei Gao wrote:
> > > > >> +               hisi,reset-bits = <0x20 0x8             /* 0: i2c0 */
> > > > >> +                                  0x20 0x10            /* 1: i2c1 */
> > > > >> +                                  0x20 0x20            /* 2: i2c2 */
> > > > >> +                                  0x20 0x8000000>;     /* 3: i2c6 */
> > > > >> +       };
> > > > >> +
> > > > >> +Specifying reset lines connected to IP modules
> > > > >> +==============================================
> > > > >> +example:
> > > > >> +
> > > > >> +        i2c0: i2c at ..... {
> > > > >> +                ...
> > > > >> +               resets = <&iomcu_rst 0>;
> > > > >> +                ...
> > > > >> +        };
> > > > > I don't really like this approach, since now the information is
> > > > > in two places. Why not put the data into the reset specifier
> > > > > directly when it is used?
> > 
> > From my point of view, with the binding above, all reset controller
> > register/bit layout information is in a single place and can be easily
> > compared to a list in the reference manual, whereas with your suggestion
> > the description of the reset controller register layout is spread
> > throughout one or even several dtsi files.
> 
> Which can be solved by tools.

True.

> > Also, since no two reset controllers are exactly the same, we get a
> > proliferation of different slightly phandle argument meanings.
> 
> phandle args are supposed to be specific to the phandle it points to. 
> Otherwise, we'd never need more than 1 cell and everything could be a 
> lookup table.

What I mean is that the clk bindings mostly use <&label index> or
<&label type index> phandles, not <&label register-offset bit-offset>
phandles. Usually the bindings don't spread information about the
register layout of the clock controller throughout the device tree,
because that is contained in the driver, as determined by the compatible
property. I assumed the same should be true for reset controllers, if
possible.

> > > > Any example, still not understand.
> > > > They are consumer and provider.
> > > 
> > > I mean in the i2c node, have
> > > 
> > > 	i2c0: i2c at ..... {
> > > 		...
> > > 		resets = <&iomcu_rst 0x20 0x8>;
> > > 		...
> > > 	}
> > 
> > There already are a few drivers that use this, and I fear people having
> > to change their bindings because new flags are needed that have not been
> > previously thought of. 
> 
> Drivers that use what?

Drivers that use <&label register-offset bit-offset> phandles instead of
<&label index> phandles.

regards
Philipp