Re: [RFC v1 1/7] clk: meson: meson8b: run from the XTAL when changing the CPU frequency

[Jerome Brunet <jbrunet@baylibre.com>]

On Wed, 2018-11-14 at 23:57 +0100, Martin Blumenstingl wrote:
> Changing the CPU clock requires changing various clocks including the
> SYS PLL. The existing meson clk-pll and clk-regmap drivers can change
> all of the relevant clocks already.
> However, changing for exampe the SYS PLL is problematic because as long
> as the CPU is running off a clock derived from SYS PLL changing the
> latter results in a full system lockup.
> Fix this system lockup by switching the CPU clock to run off the XTAL
> while we are changing the any of the clocks in the CPU clock tree.
> 
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

Original submission wasn't that far off after all ;)

Thanks for digging and fixing all the bugs around it ! It must have been quite
a challenge !

If you don't mind, I would prefer if your series put all the clock fixes
first, and this particular change just before the last one allowing RW ops.

Reviewed-by: Jerome Brunet <jbrunet@baylibre.com>

> ---
>  drivers/clk/meson/meson8b.c | 63 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 63 insertions(+)
> 
> diff --git a/drivers/clk/meson/meson8b.c b/drivers/clk/meson/meson8b.c
> index 9bd5920da0ff..40e77fe4ba7c 100644
> --- a/drivers/clk/meson/meson8b.c
> +++ b/drivers/clk/meson/meson8b.c
> @@ -1103,6 +1103,53 @@ static const struct reset_control_ops
> meson8b_clk_reset_ops = {
>  	.deassert = meson8b_clk_reset_deassert,
>  };
>  
> +struct meson8b_nb_data {
> +	struct notifier_block nb;
> +	struct clk_hw_onecell_data *onecell_data;
> +};
> +
> +static int meson8b_cpu_clk_notifier_cb(struct notifier_block *nb,
> +				       unsigned long event, void *data)
> +{
> +	struct meson8b_nb_data *nb_data =
> +		container_of(nb, struct meson8b_nb_data, nb);
> +	struct clk_hw **hws = nb_data->onecell_data->hws;
> +	struct clk_hw *cpu_clk_hw, *parent_clk_hw;
> +	struct clk *cpu_clk, *parent_clk;
> +	int ret;
> +
> +	switch (event) {
> +	case PRE_RATE_CHANGE:
> +		parent_clk_hw = hws[CLKID_XTAL];
> +		break;
> +
> +	case POST_RATE_CHANGE:
> +		parent_clk_hw = hws[CLKID_CPU_SCALE_OUT_SEL];
> +		break;
> +
> +	default:
> +		return NOTIFY_DONE;
> +	}
> +
> +	cpu_clk_hw = hws[CLKID_CPUCLK];
> +	cpu_clk = __clk_lookup(clk_hw_get_name(cpu_clk_hw));
> +
> +	parent_clk = __clk_lookup(clk_hw_get_name(parent_clk_hw));
> +
> +	ret = clk_set_parent(cpu_clk, parent_clk);
> +	if (ret)
> +		return notifier_from_errno(ret);
> +
> +	udelay(100);
> +
> +	return NOTIFY_OK;
> +}
> +
> +static struct meson8b_nb_data meson8b_cpu_nb_data = {
> +	.nb.notifier_call = meson8b_cpu_clk_notifier_cb,
> +	.onecell_data = &meson8b_hw_onecell_data,
> +};
> +
>  static const struct regmap_config clkc_regmap_config = {
>  	.reg_bits       = 32,
>  	.val_bits       = 32,
> @@ -1112,6 +1159,8 @@ static const struct regmap_config clkc_regmap_config =
> {
>  static void __init meson8b_clkc_init(struct device_node *np)
>  {
>  	struct meson8b_clk_reset *rstc;
> +	const char *notifier_clk_name;
> +	struct clk *notifier_clk;
>  	void __iomem *clk_base;
>  	struct regmap *map;
>  	int i, ret;
> @@ -1166,6 +1215,20 @@ static void __init meson8b_clkc_init(struct
> device_node *np)
>  			return;
>  	}
>  
> +	/*
> +	 * FIXME we shouldn't program the muxes in notifier handlers. The
> +	 * tricky programming sequence will be handled by the forthcoming
> +	 * coordinated clock rates mechanism once that feature is released.
> +	 */
> +	notifier_clk_name = clk_hw_get_name(&meson8b_cpu_scale_out_sel.hw);
> +	notifier_clk = __clk_lookup(notifier_clk_name);
> +	ret = clk_notifier_register(notifier_clk, &meson8b_cpu_nb_data.nb);
> +	if (ret) {
> +		pr_err("%s: failed to register the CPU clock notifier\n",
> +		       __func__);
> +		return;
> +	}
> +
>  	ret = of_clk_add_hw_provider(np, of_clk_hw_onecell_get,
>  				     &meson8b_hw_onecell_data);
>  	if (ret)