linux-kernel - [PATCH 1/5] clk: sunxi-ng: nkm: Support constraints on m/n ratio and parent rate

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Date: Mon, 18 Dec 2023 14:35:19 +0100
From: Frank Oltmanns <frank@...manns.dev>
To: Michael Turquette <mturquette@...libre.com>, 
 Stephen Boyd <sboyd@...nel.org>, Chen-Yu Tsai <wens@...e.org>, 
 Jernej Skrabec <jernej.skrabec@...il.com>, 
 Samuel Holland <samuel@...lland.org>, 
 Guido Günther <agx@...xcpu.org>, 
 Purism Kernel Team <kernel@...i.sm>, Ondrej Jirman <megi@....cz>, 
 Neil Armstrong <neil.armstrong@...aro.org>, 
 Jessica Zhang <quic_jesszhan@...cinc.com>, Sam Ravnborg <sam@...nborg.org>, 
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, 
 Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, 
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>
Cc: linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, 
 linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org, 
 dri-devel@...ts.freedesktop.org, Frank Oltmanns <frank@...manns.dev>
Subject: [PATCH 1/5] clk: sunxi-ng: nkm: Support constraints on m/n ratio
 and parent rate

The Allwinner A64 manual lists the following constraints for the
PLL-MIPI clock:
 - M/N >= 3
 - (PLL_VIDEO0)/M >= 24MHz

The PLL-MIPI clock is implemented as ccu_nkm. Therefore, add support for
these constraints.

Signed-off-by: Frank Oltmanns <frank@...manns.dev>
---
 drivers/clk/sunxi-ng/ccu_nkm.c | 23 +++++++++++++++++++++++
 drivers/clk/sunxi-ng/ccu_nkm.h |  8 ++++++++
 2 files changed, 31 insertions(+)

diff --git a/drivers/clk/sunxi-ng/ccu_nkm.c b/drivers/clk/sunxi-ng/ccu_nkm.c
index eed64547ad42..2af5c1ebd527 100644
--- a/drivers/clk/sunxi-ng/ccu_nkm.c
+++ b/drivers/clk/sunxi-ng/ccu_nkm.c
@@ -16,6 +16,20 @@ struct _ccu_nkm {
 	unsigned long	m, min_m, max_m;
 };
 
+static bool ccu_nkm_is_valid_rate(struct ccu_common *common, unsigned long parent,
+				  unsigned long n, unsigned long m)
+{
+	struct ccu_nkm *nkm = container_of(common, struct ccu_nkm, common);
+
+	if (nkm->max_mn_ratio && (m > nkm->max_mn_ratio * n))
+		return false;
+
+	if (nkm->parent_wo_nk && (parent < nkm->parent_wo_nk * m))
+		return false;
+
+	return true;
+}
+
 static unsigned long ccu_nkm_find_best_with_parent_adj(struct ccu_common *common,
 						       struct clk_hw *parent_hw,
 						       unsigned long *parent, unsigned long rate,
@@ -32,6 +46,9 @@ static unsigned long ccu_nkm_find_best_with_parent_adj(struct ccu_common *common
 
 				tmp_parent = clk_hw_round_rate(parent_hw, rate * _m / (_n * _k));
 
+				if (!ccu_nkm_is_valid_rate(common, tmp_parent, _n, _m))
+					continue;
+
 				tmp_rate = tmp_parent * _n * _k / _m;
 
 				if (ccu_is_better_rate(common, rate, tmp_rate, best_rate) ||
@@ -65,6 +82,12 @@ static unsigned long ccu_nkm_find_best(unsigned long parent, unsigned long rate,
 	for (_k = nkm->min_k; _k <= nkm->max_k; _k++) {
 		for (_n = nkm->min_n; _n <= nkm->max_n; _n++) {
 			for (_m = nkm->min_m; _m <= nkm->max_m; _m++) {
+				if ((common->reg == 0x040) && (_m > 3 * _n))
+					break;
+
+				if ((common->reg == 0x040) && (parent < 24000000 * _m))
+					continue;
+
 				unsigned long tmp_rate;
 
 				tmp_rate = parent * _n * _k / _m;
diff --git a/drivers/clk/sunxi-ng/ccu_nkm.h b/drivers/clk/sunxi-ng/ccu_nkm.h
index 6601defb3f38..d3d3eaf55faf 100644
--- a/drivers/clk/sunxi-ng/ccu_nkm.h
+++ b/drivers/clk/sunxi-ng/ccu_nkm.h
@@ -16,6 +16,12 @@
  * struct ccu_nkm - Definition of an N-K-M clock
  *
  * Clocks based on the formula parent * N * K / M
+ *
+ * @max_mn_ratio:	Maximum value for M / N.
+ * @parent_wo_nk:	The minimum rate the parent must provide after applying the divisor,
+ *			but without applying the multipliers, i.e. the contstraint
+ *			   (parent rate)/M >= parent_wo_nk
+ *			must be fulfilled.
  */
 struct ccu_nkm {
 	u32			enable;
@@ -27,6 +33,8 @@ struct ccu_nkm {
 	struct ccu_mux_internal	mux;
 
 	unsigned int		fixed_post_div;
+	unsigned long		max_mn_ratio;
+	unsigned long           parent_wo_nk;
 
 	struct ccu_common	common;
 };

-- 
2.43.0