Re: [PATCH v14 1/4] clk: mediatek: Add MT2701 clock support

James Liao
2016-11-01T09:23:54Z

Hi Stephen,

On Mon, 2016-10-31 at 11:06 -0700, Stephen Boyd wrote:
> On 10/31, James Liao wrote:
> > On Thu, 2016-10-27 at 18:17 -0700, Stephen Boyd wrote:
> > > On 10/21, Erin Lo wrote:
> > > > @@ -244,3 +256,31 @@ void mtk_clk_register_composites(const struct mtk_composite *mcs,
> > > > clk_data->clks[mc->id] = clk;
> > > > }
> > > > }
> > > > +
> > > > +void mtk_clk_register_dividers(const struct mtk_clk_divider *mcds,
> > > > + int num, void __iomem *base, spinlock_t *lock,
> > > > + struct clk_onecell_data *clk_data)
> > > > +{
> > > > + struct clk *clk;
> > > > + int i;
> > > > +
> > > > + for (i = 0; i < num; i++) {
> > > > + const struct mtk_clk_divider *mcd = &mcds[i];
> > > > +
> > > > + if (clk_data && !IS_ERR_OR_NULL(clk_data->clks[mcd->id]))
> > >
> > > NULL is a valid clk. IS_ERR_OR_NULL is usually wrong.
> >
> > Why NULL is a valid clk?
>
> Perhaps at some point we'll want to return a NULL pointer to
> clk_get() callers so that they can handle things like optional
> clocks easily without having any storage requirements. I don't
> know if we'll ever do that, but that's just a possibility.
>
> >
> > clk_data is designed for multiple initialization from different clock
> > types, such as infra_clk_data in clk-mt2701.c. So it will ignore valid
> > clocks to avoid duplicated clock registration. Here I assume a clock
> > pointer with error code or NULL to be an invalid (not initialized)
> > clock.
> >
>
> Ok. Would it be possible to initialize the array with all error
> pointers? That would make things less error prone, but it

Yes. Current mtk_alloc_clk_data() implementation init all elements with
ERR_PTR(-ENOENT).

> probably doesn't matter at all anyway because this is done during
> registration time. IS_ERR_OR_NULL makes me take a second look
> each time, because it's usually wrong.

I see. Although currently all Mediatek clk drivers use
mtk_alloc_clk_data() to allocate clk_data, I would like to keep the
flexibility to support zero-initialized clk_data such as a static
structure. So I prefer to treat a NULL pointer as an uninitialized
clock.

Best regards,

James