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SubjectRe: [PATCH v5 4/4] clk: bd71837: Add driver for BD71837 PMIC clock
On Tue, Jun 12, 2018 at 11:23:54AM +0300, Matti Vaittinen wrote:
> Hello Stephen,
>
> Thanks again for the review. I'll do new patch which fixes these issues.
>
> On Tue, Jun 12, 2018 at 12:44:11AM -0700, Stephen Boyd wrote:
> > Quoting Matti Vaittinen (2018-06-04 06:19:13)
> > > +}
> > > +
> > > +static unsigned long bd71837_clk_recalc_rate(struct clk_hw *hw,
> > > + unsigned long parent_rate)
> > > +{
> > > + struct bd71837_clk *c = container_of(hw, struct bd71837_clk, hw);
> > > +
> > > + return c->rate;
> > > +}
> > > +
> > > +static const struct clk_ops bd71837_clk_ops = {
> > > + .recalc_rate = &bd71837_clk_recalc_rate,
> > > + .prepare = &bd71837_clk_enable,
> > > + .unprepare = &bd71837_clk_disable,
> > > + .is_prepared = &bd71837_clk_is_enabled,
> > > +};
> > > +
> > > +static int bd71837_clk_probe(struct platform_device *pdev)
> > > +{
> > > + struct bd71837_clk *c;
> > > + int rval = -ENOMEM;
> > > + struct bd71837 *mfd = dev_get_drvdata(pdev->dev.parent);
> > > + struct clk_init_data init = {
> > > + .name = "bd71837-32k-out",
> > > + .ops = &bd71837_clk_ops,
> > > + };
> > > +
> > > + c = devm_kzalloc(&pdev->dev, sizeof(*c), GFP_KERNEL);
> > > + if (!c)
> > > + goto err_out;
> > > +
> > > + c->reg = BD71837_REG_OUT32K;
> > > + c->mask = BD71837_OUT32K_EN;
> > > + c->rate = BD71837_CLK_RATE;
> >
> > The PMIC has an 'XIN' pin that would be the clk input for this chip, and
> > the output clk, this driver, would specify that xin clock as the parent.
> > The 'xin' clock would then be listed in DT as a fixed-rate clock. That
> > way this driver doesn't hardcode the frequency.
>
> I see. This makes sense. I need to verify from HW colleagues whether
> this chip has internal oscillator or not. I originally thought we have
> on-chip oscillator - but as you say, we do have XIN pin in documentation.
> So now I am not sure if the test board I have contains oscillator driving
> the clk on PMIC - or if the PMIC has internal oscillator. I'll clarify this.

It really turned out that the PMIC just acts as a clock buffer. So I do
as you suggested and add lookup for parent clock to the driver. I
planned to do it so that if no parent is found from DT - then we assume
the 32.768KHz clock (as described in documentation). Eg, something along
the lines:

init.parent_names = of_clk_get_parent_name(pdev->dev.parent->of_node, 0);
if (init.parent_names) {
init.num_parents = 1;
} else {
/* If parent is not given from DT we assume the typical use-case with
* 32.768 KHz oscillator for RTC (Maybe we could just error out here?)
*/
c->rate = BD71837_CLK_RATE;
bd71837_clk_ops.recalc_rate = &bd71837_clk_recalc_rate;
}

Does this make sense?

Br,
Matti Vaittinen

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