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

Boris Brezillon
2015-04-19T15:30:06Z

Hi Heiko,

On Sun, 19 Apr 2015 14:13:04 +0200
Heiko Stübner <heiko@sntech.de> wrote:

> Hi Boris,
>
> Am Freitag, 17. April 2015, 09:29:28 schrieb Boris Brezillon:
> > 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.
> >
> > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> > ---
>
> On a rk3288-veyron-pinky with the fix described below:
> Tested-by: Heiko Stuebner <heiko@sntech.de>
>
>
> > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > index fa5a00e..1462ddc 100644
> > --- a/drivers/clk/clk.c
> > +++ b/drivers/clk/clk.c
> > @@ -1640,8 +1643,10 @@ static struct clk_core *clk_calc_new_rates(struct
> > clk_core *clk, &parent_hw);
> > parent = parent_hw ? parent_hw->core : NULL;
> > } else if (clk->ops->round_rate) {
> > - new_rate = clk->ops->round_rate(clk->hw, rate,
> > - &best_parent_rate);
> > + if (clk->ops->round_rate(clk->hw, &new_rate,
> > + &best_parent_rate))
> > + return NULL;
> > +
> > if (new_rate < min_rate || new_rate > max_rate)
> > return NULL;
> > } else if (!parent || !(clk->flags & CLK_SET_RATE_PARENT)) {
>
> This is using new_rate uninitialized when calling into the round_rate
> callback. Which in turn pushed my PLLs up to 2.2GHz :-)

Indeed, thanks for the fix.

[...]

>
>
> And as I've stumbled onto this recently too, the clock-maintainership has
> expanded to Stephen Boyd and linux-clk@vger.kernel.org .

Noted. I'll add Stephen and the new linux-clk ML in the recipient list
next time.

Best Regards,

Boris

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