Re: [PATCH v2 1/2] clk: change clk_ops' ->round_rate() prototype

Boris Brezillon
2015-06-05T11:38:03Z

Hi Paul,

On Thu, 4 Jun 2015 23:02:25 +0000 (UTC)
Paul Walmsley <paul@pwsan.com> wrote:

> Hi folks
>
> just a brief comment on this one:
>
> On Thu, 30 Apr 2015, Boris Brezillon wrote:
>
> > Clock rates are stored in an unsigned long field, but ->round_rate()
> > (which returns a rounded rate from a requested one) returns a long
> > value (errors are reported using negative error codes), which can lead
> > to long overflow if the clock rate exceed 2Ghz.
> >
> > Change ->round_rate() prototype to return 0 or an error code, and pass the
> > requested rate as a pointer so that it can be adjusted depending on
> > hardware capabilities.
>
> ...
>
> > diff --git a/Documentation/clk.txt b/Documentation/clk.txt
> > index 0e4f90a..fca8b7a 100644
> > --- a/Documentation/clk.txt
> > +++ b/Documentation/clk.txt
> > @@ -68,8 +68,8 @@ the operations defined in clk.h:
> > int (*is_enabled)(struct clk_hw *hw);
> > unsigned long (*recalc_rate)(struct clk_hw *hw,
> > unsigned long parent_rate);
> > - long (*round_rate)(struct clk_hw *hw,
> > - unsigned long rate,
> > + int (*round_rate)(struct clk_hw *hw,
> > + unsigned long *rate,
> > unsigned long *parent_rate);
> > long (*determine_rate)(struct clk_hw *hw,
> > unsigned long rate,
>
> I'd suggest that we should probably go straight to 64-bit rates. There
> are already plenty of clock sources that can generate rates higher than
> 4GiHz.

Yep, that was something I was considering too. If Stephen agrees I'll
change that in the next version.
BTW, you're referring to the second version of this patch, but things
have changed a bit: Stephen recommended to only modify the
->determine_rate() prototype and pass a structure instead of a list of
arguments.
Here is the last version of this series [1].

Best Regards,

Boris

[1]http://patchwork.linux-mips.org/patch/10092/

--
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering