[PATCH 2/2] clocksource/drivers/renesas-ostm: Add RZ/G2L OSTM support

[Philipp Zabel]

On Wed, 2021-11-10 at 11:37 +0000, Biju Das wrote:
> Hi Philipp and Geert,
> 
> Thanks for the feedback.
> 
> > Subject: Re: [PATCH 2/2] clocksource/drivers/renesas-ostm: Add RZ/G2L OSTM
> > support
> > 
> > Hi Geert, Biju,
> > 
> > On Wed, 2021-11-10 at 11:27 +0100, Geert Uytterhoeven wrote:
> > > Hi Biju,
> > > 
> > > On Wed, Nov 10, 2021 at 9:32 AM Biju Das <biju.das.jz at bp.renesas.com>
> > wrote:
> > > > RZ/G2L SoC has Generic Timer Module(a.k.a OSTM) which needs to
> > > > deassert the reset line before accessing any registers.
> > > > 
> > > > This patch adds an entry point for RZ/G2L so that we can deassert
> > > > the reset line in probe callback.
> > > > 
> > > > Signed-off-by: Biju Das <biju.das.jz at bp.renesas.com>
> > > > Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj at bp.renesas.com>
> > > 
> > > Thanks for your patch!
> > > 
> > > > --- a/drivers/clocksource/renesas-ostm.c
> > > > +++ b/drivers/clocksource/renesas-ostm.c
> > > > @@ -209,3 +211,39 @@ static int __init ostm_init(struct device_node
> > > > *np)
> > > >  }
> > > > 
> > > >  TIMER_OF_DECLARE(ostm, "renesas,ostm", ostm_init);
> > > 
> > > Background: this driver uses TIMER_OF_DECLARE() because the OSTM is
> > > the system timer on RZ/A SoCs, which do not have the ARM architectured
> > > timer.  RZ/G2L does have the ARM architectured timer.
> > 
> > Thanks.
> > 
> > > > +
> > > > +#ifdef CONFIG_ARCH_R9A07G044
> > > > +static int __init ostm_probe(struct platform_device *pdev) {
> > > > +       struct device *dev = &pdev->dev;
> > > > +       struct reset_control *rstc;
> > > > +       int ret;
> > > > +
> > > > +       rstc = devm_reset_control_get_exclusive(dev, NULL);
> > > > +       if (IS_ERR(rstc))
> > > > +               return dev_err_probe(dev, PTR_ERR(rstc), "failed to
> > > > + get reset");
> > > > +
> > > > +       reset_control_deassert(rstc);
> > > > +
> > > > +       ret = ostm_init(dev->of_node);
> > > > +       if (ret) {
> > > > +               reset_control_assert(rstc);
> > > > +               return ret;
> > > > +       }
> > > > +
> > > > +       return 0;
> > > > +}
> > > > +
> > > > +static const struct of_device_id ostm_of_table[] = {
> > > > +       { .compatible = "renesas,rzg2l-ostm", },
> > > 
> > > I believe the OSTM block on RZ/G2L is identical to the one on RZ/A,
> > > and the requirement to deassert its module reset is an SoC integration
> > > feature on RZ/G2L.  Hence the driver should match on "renesas,ostm"
> > > for both?
> > 
> > If that is the case, the reset could be made required for
> >   compatible = "renesas,r9a07g044-ostm", "renesas,ostm"; in the .yaml
> > file.
> > 
> > > So my suggestion would be to include the reset handling in ostm_init()
> > > instead, but make it optional, and error out in case of -EPROBE_DEFER.
> > > 
> > > In case initialization from TIMER_OF_DECLARE() failed, the platform
> > > driver can kick in later and retry.
> > > 
> > > However, it seems __of_reset_control_get() ignores all errors,
> > > including -EPROBE_DEFER, if optional is true, so this won't work?
> > > 
> > > Philipp: is that correct? If yes, ostm_init() has to check the
> > > presence of a resets property to see if the reset is optional or
> > required.
> > 
> > No, __of_reset_control_get() should only replace its -ENOENT return value
> > due to errors from of_property_match_string() and
> > of_parse_phandle_with_args() with NULL. Anything else I'd consider a bug.
> > 
> > Specifically, -EPROBE_DEFER is still returned if no existing rcdev is
> > found matching the successful "resets" phandle lookup. So
> > 
> > 	rstc = devm_reset_control_get_optional_exclusive(dev, NULL);
> 
> In this case, How do we get dev here from device_node, as device is not available at this point?

Oh, right.
We are missing an of_reset_control_get_optional_exclusive() for this:

static inline struct reset_control *of_reset_control_get_optional_exclusive(
		struct device_node *node, const char *id)
{
	return __of_reset_control_get(node, id, 0, false, true, true);
}

regards
Philipp