Re: [PATCH v2 06/16] clk: starfive: Add JH7100 clock generator driver

Emil Renner Berthing
2021-10-27T10:24:23Z

On Wed, 27 Oct 2021 at 02:54, Stephen Boyd <sboyd@kernel.org> wrote:
> Quoting Emil Renner Berthing (2021-10-26 15:35:36)
> > On Tue, 26 Oct 2021 at 22:20, Stephen Boyd <sboyd@kernel.org> wrote:
> > > Quoting Emil Renner Berthing (2021-10-21 10:42:13)
> > > > +};
> > > > +
> > > > +struct clk_starfive_jh7100_priv {
> > > > + /* protect registers against overlapping read-modify-write */
> > > > + spinlock_t rmw_lock;
> > >
> > > Does overlapping mean concurrent?
> >
> > Yes, sorry.
> >
> > > Do different clks share the same registers?
> >
> > No, each clock has their own register, but they use that register both
> > to gate the clock and other configuration. The Locking chapter of
> > Documentation/driver-api/clk.rst talks about the prepare lock and the
> > enable lock and then says:
> > "However, access to resources that are shared between operations of
> > the two groups needs to be protected by the drivers. An example of
> > such a resource would be a register that controls both the clock rate
> > and the clock enable/disable state."
>
> Alright got it. Maybe say "protect clk enable and set rate from
> happening at the same time".
>
> >
> > > > + return ERR_PTR(-EINVAL);
> > > > + }
> > > > +
> > > > + if (idx >= JH7100_CLK_PLL0_OUT)
> > > > + return priv->pll[idx - JH7100_CLK_PLL0_OUT];
> > > > +
> > > > + return &priv->reg[idx].hw;
> > > > +}
> > > > +
> > > > +static int __init clk_starfive_jh7100_probe(struct platform_device *pdev)
> > >
> > > Drop __init as this can be called after kernel init is over.
> >
> > Oh interesting, I'd like to know when that can happen. The comment for
> > the builtin_platform_driver macro says it's just a wrapper for
>
> I thought this was using module_platform_driver() macro?
>
> > device_initcall.
> >
> > Won't we then need to remove all the __initconst tags too since the
> > probe function walks through jh7100_clk_data which eventually
> > references all __initconst data?
>
> Yes. If it's builtin_platform_driver() it can't be a module/tristate
> Kconfig, in which case all the init markings can stay.

Yes, it's already bool in the Kconfig file. After looking into this I
think it's better to do like the rockchip drivers and use
builtin_platform_driver_probe to make sure the probe function only
called at kernel init time:

static struct platform_driver clk_starfive_jh7100_driver = {
.driver = {
.name = "clk-starfive-jh7100",
.of_match_table = clk_starfive_jh7100_match,
.suppress_bind_attrs = true,
},
};
builtin_platform_driver_probe(clk_starfive_jh7100_driver,
clk_starfive_jh7100_probe);

@Andy: is the supress_bind_attrs what you were asking about?

> > > > +
> > > > + clk->hw.init = &init;
> > > > + clk->idx = idx;
> > > > + clk->max = jh7100_clk_data[idx].max;
> > > > +
> > > > + ret = clk_hw_register(priv->dev, &clk->hw);
> > >
> > > Why not use devm_clk_hw_register()?
> >
> > I probably could. Just for my understanding that's just to avoid the
> > loop on error below, because as a builtin driver the device won't
> > otherwise go away, right?
>
> Yes
>
> >
> > > > + if (ret)
> > > > + goto err;
> > > > + }
> > > > +
> > > > + ret = devm_of_clk_add_hw_provider(priv->dev, clk_starfive_jh7100_get, priv);
> > > > + if (ret)
> > > > + goto err;
> > > > +
> > > > + return 0;
> > > > +err:
> > > > + while (idx)
> > > > + clk_hw_unregister(&priv->reg[--idx].hw);
> > > > + return ret;
> > > > +}
> > > > +
> > > > +static const struct of_device_id clk_starfive_jh7100_match[] = {
> > > > + { .compatible = "starfive,jh7100-clkgen" },
> > > > + { /* sentinel */ }
> > > > +};
> > >
> > > Please add MODULE_DEVICE_TABLE()
> >
> > Will do!
>
> If it's never going to be a module then don't add any module_* things.

So does that just mean no MODULE_DEVICE_TABLE or should I also remove
MODULE_DESCRIPTION, MODULE_AUTHOR and MODULE_LICENSE? I'm just double
checking because the rockchip drivers seem to have MODULE_DESCRIPTION
and MODULE_LICENSE lines.