Re: [PATCH v4 3/6] clk: introduce the common clock framework

[Richard Zhao]

On Wed, Jan 04, 2012 at 05:01:43PM -0800, Turquette, Mike wrote:
> On Wed, Jan 4, 2012 at 6:32 AM, Rob Herring <robherring2@xxxxxxxxx> wrote:
> > On 01/03/2012 08:15 PM, Richard Zhao wrote:
> >> On Fri, Dec 16, 2011 at 04:45:48PM -0800, Turquette, Mike wrote:
> >>> On Wed, Dec 14, 2011 at 5:18 AM, Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote:
> >>>> On Tue, 13 Dec 2011, Mike Turquette wrote:
> >
> > snip
> >
> >>>>> +/**
> >>>>> + * clk_init - initialize the data structures in a struct clk
> >>>>> + * @dev: device initializing this clk, placeholder for now
> >>>>> + * @clk: clk being initialized
> >>>>> + *
> >>>>> + * Initializes the lists in struct clk, queries the hardware for the
> >>>>> + * parent and rate and sets them both.  Adds the clk to the sysfs tree
> >>>>> + * topology.
> >>>>> + *
> >>>>> + * Caller must populate clk->name and clk->flags before calling
> >>>>
> >>>> I'm not too happy about this construct. That leaves struct clk and its
> >>>> members exposed to the world instead of making it a real opaque
> >>>> cookie. I know from my own painful experience, that this will lead to
> >>>> random fiddling in that data structure in drivers and arch code just
> >>>> because the core code has a shortcoming.
> >>>>
> >>>> Why can't we make struct clk a real cookie and confine the data
> >>>> structure to the core code ?
> >>>>
> >>>> That would change the init call to something like:
> >>>>
> >>>> struct clk *clk_init(struct device *dev, const struct clk_hw *hw,
> >>>>                     struct clk *parent)
> >>>>
> >>>> And have:
> >>>> struct clk_hw {
> >>>>       struct clk_hw_ops *ops;
> >>>>       const char        *name;
> >>>>       unsigned long     flags;
> >>>> };
> >>>>
> >>>> Implementers can do:
> >>>> struct my_clk_hw {
> >>>>       struct clk_hw    hw;
> >>>>       mydata;
> >>>> };
> >>>>
> >>>> And then change the clk ops callbacks to take struct clk_hw * as an
> >>>> argument.
> >> We have to define static clocks before we adopt DT binding.
> >> If clk is opaque and allocate memory in clk core, it'll make hard
> >> to define static clocks. And register/init will pass a long parameter
> >> list.
> >
> > DT is not a prerequisite for having dynamically created clocks. You can
> > make clock init dynamic without DT.
I can not find clock info at runtime without DT. If I use static info, I
find it was hard/strange to define and register it, using Mike's early patches.
> 
> Agreed.
> 
> > What data goes in struct clk vs. struct clk_hw could change over time.
> > So perhaps we can start with some data in clk_hw and plan to move it to
> > struct clk later. Even if almost everything ends up in clk_hw initially,
> > at least the structure is in place to have common, core-only data
> > separate from platform data.
> 
> What is the point of this?
> 
> The original clk_hw was defined simply as:
> 
> struct clk_hw {
>         struct clk *clk;
> };
> 
> It's only purpose in life was as a handle for navigation between the
> opaque struct clk and the hardware-specific struct my_clk_hw.  struct
> clk_hw is defined in clk.h and everyone can see it.  If we're suddenly
> OK putting clk data in this structure then why bother with an opaque
> struct clk at all?
I think Rob meant one time a step to make it opaque. But it'll make
clk core always changing, easier mess, and let clk driver confused.
> 
> > What is the actual data you need to be static and accessible to the
> > platform code? A ptr to parent clk is the main thing I've seen for
> > static initialization. So make the parent ptr be struct clk_hw* and
> > allow the platforms to access.
> 
> To answer your question on what data we're trying to expose: platform
> code commonly needs the parent pointer and the clk rate (and by
> extension, the rate of the parent).  For debug/error prints it is also
> nice to have the clk name.  Generic clk flags are also conceivably
> something that platform code might want.
> 
> I'd like to spin the question around: if we're OK exposing some stuff
> (in your example above, the parent pointer), then what clk data are
> you trying to hide?
> 
> Regards,
> Mike
> 
> >
> > Rob
> 

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