Re: [PATCH v2 4/6] clk: hi6220: Clock driver support for Hisilicon hi6220 SoC

[YiPing Xu]

å 2015/4/13 23:34, Arnd Bergmann åé:
> On Monday 13 April 2015 21:57:46 Bintian wrote:
> > Hello Arnd,
> >
> > Thanks for your code review.
> >
> > On 2015/4/13 21:30, Arnd Bergmann wrote:
> > > On Monday 13 April 2015 17:17:38 Bintian Wang wrote:
> > > > +#define HI6220_CFG_CSI2PHY     8
> > > > +#define HI6220_ISP_SCLK_GATE   9
> > > > +#define HI6220_ISP_SCLK_GATE1  10
> > > > +#define HI6220_ADE_CORE_GATE   11
> > > > +#define HI6220_CODEC_VPU_GATE  12
> > > > +#define HI6220_MED_SYSPLL      13
> > > > +
> > > > +/* mux clocks */
> > > > +#define HI6220_1440_1200       20
> > > > +#define HI6220_1000_1200       21
> > > > +#define HI6220_1000_1440       22
> > > > +
> > > > +/* divider clocks */
> > > > +#define HI6220_CODEC_JPEG      30
> > > > +#define HI6220_ISP_SCLK_SRC    31
> > > > +#define HI6220_ISP_SCLK1       32
> > >
> > > The numbers seem rather arbitrary, and you have both holes as well as duplicate
> > > numbers here. I would suggest you do one of two things instead:
>
> > I just worry about some special clocks may be added later so keep some
> > holes for them;
> >
> > The duplicate numbers means clocks belong to different system control
> > domains.
>
> I don't understand. How would there be additional clocks added later?
> Wouldn't that be a new chip?

  There are some clocks not used in linux system. e.g, some clocks are 
used in base band processor. So, some numbers are not defined here.

> If you have separate system control domains, doesn't that mean that you
> also have separate DT bindings?
>
> > > a) have a separate header file per clock driver and make all the
> > >      numbers unique and consecutive within that header
> > >
> > > b) use the same numbers as the hardware registers so you can put the
> > >      numbers directly into the dts and don't need a header to create
> > >      an artificial ABI between the clock driver and the boot loader.
> > This header file will be used by device tree (I like using the clock
> > name instead "magic number" in dts :) )
>
> That's not how it works though: The dts file is the place to define
> the hardware numbers, we do that for all sorts of numbers: interrupts,
> gpios, register ranges etc are all defined in dts to avoid putting
> magic numbers in external header files.
>
> There are some cases where it gets too ugly for clock controllers
> that are highly irregular, but yours doesn't seem to be that kind.
>
> E.g. all the fixed rate clocks should just be separate device nodes,
> which lets you remove the binding for that node.
>
> > so how about keep them in one header file and let dts just include
> > one header file (not four files), but remove the holes?
>
> The header files constantly cause problems with merge dependencies,
> and we have some other companies that keep releasing new chips
> that each time require a new header file. If hisilicon plans to make
> more chips like this one, please consider coming up with more
> generic bindings to avoid this.
>
> 	Arnd
>
> .


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