clk: rockchip: handle mux dependency of fractional dividers

The fractional dividers of Rockchip SoCs contain an "auto-gating-feature"
that requires the downstream mux to actually point to the fractional
divider and the fractional divider gate to be enabled, for it to really
accept changes to the divider ratio.

The downstream muxes themselfs are not generic enough to include them
directly into the fractional divider, as they have varying sources of
parent clocks including not only clocks related to the fractional
dividers but other clocks as well.

To solve this, allow our clock branches to specify direct child clock-
branches in the new child property, let the fractional divider register
its downstream mux through this and add a clock notifier that temporarily
switches the mux setting when it notices rate changes to the fractional
divider.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Reviewed-by: Sjoerd Simons <sjoerd.simons@collabora.co.uk>
Signed-off-by: Michael Turquette <mturquette@baylibre.com>

drivers/clk/rockchip/clk.c

@@ -102,22 +102,82 @@ static struct clk *rockchip_clk_register_branch(const char *name,
 	return clk;
 }
 
+struct rockchip_clk_frac {
+	struct notifier_block			clk_nb;
+	struct clk_fractional_divider		div;
+	struct clk_gate				gate;
+
+	struct clk_mux				mux;
+	const struct clk_ops			*mux_ops;
+	int					mux_frac_idx;
+
+	bool					rate_change_remuxed;
+	int					rate_change_idx;
+};
+
+#define to_rockchip_clk_frac_nb(nb) \
+			container_of(nb, struct rockchip_clk_frac, clk_nb)
+
+static int rockchip_clk_frac_notifier_cb(struct notifier_block *nb,
+					 unsigned long event, void *data)
+{
+	struct clk_notifier_data *ndata = data;
+	struct rockchip_clk_frac *frac = to_rockchip_clk_frac_nb(nb);
+	struct clk_mux *frac_mux = &frac->mux;
+	int ret = 0;
+
+	pr_debug("%s: event %lu, old_rate %lu, new_rate: %lu\n",
+		 __func__, event, ndata->old_rate, ndata->new_rate);
+	if (event == PRE_RATE_CHANGE) {
+		frac->rate_change_idx = frac->mux_ops->get_parent(&frac_mux->hw);
+		if (frac->rate_change_idx != frac->mux_frac_idx) {
+			frac->mux_ops->set_parent(&frac_mux->hw, frac->mux_frac_idx);
+			frac->rate_change_remuxed = 1;
+		}
+	} else if (event == POST_RATE_CHANGE) {
+		/*
+		 * The POST_RATE_CHANGE notifier runs directly after the
+		 * divider clock is set in clk_change_rate, so we'll have
+		 * remuxed back to the original parent before clk_change_rate
+		 * reaches the mux itself.
+		 */
+		if (frac->rate_change_remuxed) {
+			frac->mux_ops->set_parent(&frac_mux->hw, frac->rate_change_idx);
+			frac->rate_change_remuxed = 0;
+		}
+	}
+
+	return notifier_from_errno(ret);
+}
+
 static struct clk *rockchip_clk_register_frac_branch(const char *name,
 		const char *const *parent_names, u8 num_parents,
 		void __iomem *base, int muxdiv_offset, u8 div_flags,
 		int gate_offset, u8 gate_shift, u8 gate_flags,
-		unsigned long flags, spinlock_t *lock)
+		unsigned long flags, struct rockchip_clk_branch *child,
+		spinlock_t *lock)
 {
+	struct rockchip_clk_frac *frac;
 	struct clk *clk;
 	struct clk_gate *gate = NULL;
 	struct clk_fractional_divider *div = NULL;
 	const struct clk_ops *div_ops = NULL, *gate_ops = NULL;
 
-	if (gate_offset >= 0) {
-		gate = kzalloc(sizeof(*gate), GFP_KERNEL);
-		if (!gate)
-			return ERR_PTR(-ENOMEM);
+	if (muxdiv_offset < 0)
+		return ERR_PTR(-EINVAL);
 
+	if (child && child->branch_type != branch_mux) {
+		pr_err("%s: fractional child clock for %s can only be a mux\n",
+		       __func__, name);
+		return ERR_PTR(-EINVAL);
+	}
+
+	frac = kzalloc(sizeof(*frac), GFP_KERNEL);
+	if (!frac)
+		return ERR_PTR(-ENOMEM);
+
+	if (gate_offset >= 0) {
+		gate = &frac->gate;
 		gate->flags = gate_flags;
 		gate->reg = base + gate_offset;
 		gate->bit_idx = gate_shift;
@@ -125,13 +185,7 @@ static struct clk *rockchip_clk_register_frac_branch(const char *name,
 		gate_ops = &clk_gate_ops;
 	}
 
-	if (muxdiv_offset < 0)
-		return ERR_PTR(-EINVAL);
-
-	div = kzalloc(sizeof(*div), GFP_KERNEL);
-	if (!div)
-		return ERR_PTR(-ENOMEM);
-
+	div = &frac->div;
 	div->flags = div_flags;
 	div->reg = base + muxdiv_offset;
 	div->mshift = 16;
@@ -147,7 +201,61 @@ static struct clk *rockchip_clk_register_frac_branch(const char *name,
 				     NULL, NULL,
 				     &div->hw, div_ops,
 				     gate ? &gate->hw : NULL, gate_ops,
-				     flags);
+				     flags | CLK_SET_RATE_UNGATE);
+	if (IS_ERR(clk)) {
+		kfree(frac);
+		return clk;
+	}
+
+	if (child) {
+		struct clk_mux *frac_mux = &frac->mux;
+		struct clk_init_data init;
+		struct clk *mux_clk;
+		int i, ret;
+
+		frac->mux_frac_idx = -1;
+		for (i = 0; i < child->num_parents; i++) {
+			if (!strcmp(name, child->parent_names[i])) {
+				pr_debug("%s: found fractional parent in mux at pos %d\n",
+					 __func__, i);
+				frac->mux_frac_idx = i;
+				break;
+			}
+		}
+
+		frac->mux_ops = &clk_mux_ops;
+		frac->clk_nb.notifier_call = rockchip_clk_frac_notifier_cb;
+
+		frac_mux->reg = base + child->muxdiv_offset;
+		frac_mux->shift = child->mux_shift;
+		frac_mux->mask = BIT(child->mux_width) - 1;
+		frac_mux->flags = child->mux_flags;
+		frac_mux->lock = lock;
+		frac_mux->hw.init = &init;
+
+		init.name = child->name;
+		init.flags = child->flags | CLK_SET_RATE_PARENT;
+		init.ops = frac->mux_ops;
+		init.parent_names = child->parent_names;
+		init.num_parents = child->num_parents;
+
+		mux_clk = clk_register(NULL, &frac_mux->hw);
+		if (IS_ERR(mux_clk))
+			return clk;
+
+		rockchip_clk_add_lookup(mux_clk, child->id);
+
+		/* notifier on the fraction divider to catch rate changes */
+		if (frac->mux_frac_idx >= 0) {
+			ret = clk_notifier_register(clk, &frac->clk_nb);
+			if (ret)
+				pr_err("%s: failed to register clock notifier for %s\n",
+						__func__, name);
+		} else {
+			pr_warn("%s: could not find %s as parent of %s, rate changes may not work\n",
+				__func__, name, child->name);
+		}
+	}
 
 	return clk;
 }
@@ -251,7 +359,8 @@ void __init rockchip_clk_register_branches(
 				list->parent_names, list->num_parents,
 				reg_base, list->muxdiv_offset, list->div_flags,
 				list->gate_offset, list->gate_shift,
-				list->gate_flags, flags, &clk_lock);
+				list->gate_flags, flags, list->child,
+				&clk_lock);
 			break;
 		case branch_gate:
 			flags |= CLK_SET_RATE_PARENT;

drivers/clk/rockchip/clk.h

@@ -265,6 +265,7 @@ struct rockchip_clk_branch {
 	int				gate_offset;
 	u8				gate_shift;
 	u8				gate_flags;
+	struct rockchip_clk_branch	*child;
 };
 
 #define COMPOSITE(_id, cname, pnames, f, mo, ms, mw, mf, ds, dw,\
@@ -399,6 +400,24 @@ struct rockchip_clk_branch {
 		.gate_flags	= gf,				\
 	}
 
+#define COMPOSITE_FRACMUX(_id, cname, pname, f, mo, df, go, gs, gf, ch) \
+	{							\
+		.id		= _id,				\
+		.branch_type	= branch_fraction_divider,	\
+		.name		= cname,			\
+		.parent_names	= (const char *[]){ pname },	\
+		.num_parents	= 1,				\
+		.flags		= f,				\
+		.muxdiv_offset	= mo,				\
+		.div_shift	= 16,				\
+		.div_width	= 16,				\
+		.div_flags	= df,				\
+		.gate_offset	= go,				\
+		.gate_shift	= gs,				\
+		.gate_flags	= gf,				\
+		.child		= &(struct rockchip_clk_branch)ch, \
+	}
+
 #define MUX(_id, cname, pnames, f, o, s, w, mf)			\
 	{							\
 		.id		= _id,				\