linux-kernel - [PATCH 07/13] clk: detect unintended rate changes

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Message-Id: <20230918-imx8mp-dtsi-v1-7-1d008b3237c0@skidata.com>
Date:   Mon, 18 Sep 2023 00:40:03 +0200
From:   Benjamin Bara <bbara93@...il.com>
To:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Abel Vesa <abelvesa@...nel.org>, Peng Fan <peng.fan@....com>
Cc:     Frank Oltmanns <frank@...manns.dev>,
        Maxime Ripard <mripard@...nel.org>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-clk@...r.kernel.org,
        Benjamin Bara <benjamin.bara@...data.com>
Subject: [PATCH 07/13] clk: detect unintended rate changes

From: Benjamin Bara <benjamin.bara@...data.com>

As we now keep track of the clocks which are allowed to change - namely
the ones which are along the ancestor line between the rate trigger and
the top-most changed clock, we can run through the subtree of changes
and look for unexpected ones. Shared parents must set their rate in a
way, that all consumer-configured rates are respected. As this is
sometimes not possible and clocks sometime doesn't require the *exact*
rate, we might have to find a way to find out if it is *exact enough*.
Then we could fix it in the core.

Signed-off-by: Benjamin Bara <benjamin.bara@...data.com>
---
 drivers/clk/clk.c | 83 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 82c65ed432c5..faececc44c28 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -2280,6 +2280,74 @@ static struct clk_core *clk_calc_new_rates(struct clk_core *core,
 	return top;
 }
 
+/*
+ * If the changed clock is consumer-configured, but not an ancestor of the
+ * trigger, it is most likely an unintended change. As a workaround, we try to
+ * set the rate back to the old without changing the parent. If this is not
+ * possible, the change should not have been suggested in the first place.
+ */
+static struct clk_core *clk_detect_unintended_rate_changes(struct clk_core *core,
+							   bool fix)
+{
+	struct clk_core *child, *tmp_clk;
+
+	if (core->rate == core->new_rate)
+		return NULL;
+
+	if (core->set_rate && core != rate_trigger_clk->core &&
+	    !clk_core_is_ancestor(rate_trigger_clk->core, core)) {
+		struct clk_core *parent = core->new_parent ? : core->parent;
+		struct clk_rate_request req;
+
+		pr_debug("%s: unintended change by %s (%lu -> %lu)\n", core->name,
+			 rate_trigger_clk->core->name, core->rate, core->new_rate);
+
+		if (fix) {
+			clk_hw_init_rate_request(core->hw, &req, core->rate);
+			req.best_parent_rate = parent->new_rate;
+			req.best_parent_hw = parent->hw;
+
+			if (clk_core_round_rate_nolock(core, &req))
+				return core;
+
+			/* TODO: how close is close enough? */
+			if (req.rate != core->rate) {
+				pr_debug("%s: %s fix failed, req=%lu, sugg=%lu\n",
+					 __func__, core->name, core->rate, req.rate);
+				return core;
+			}
+			if (req.best_parent_rate != parent->new_rate ||
+			    req.best_parent_hw != parent->hw) {
+				pr_debug("%s: %s fix failed, req=%s@%lu, sugg=%s@%lu\n",
+					 __func__, core->name, parent->name,
+					 parent->new_rate,
+					 req.best_parent_hw->core->name,
+					 req.best_parent_rate);
+				return core;
+			}
+
+			core->new_rate = core->rate;
+		}
+		return NULL;
+	}
+
+	hlist_for_each_entry(child, &core->children, child_node) {
+		if (child->new_parent && child->new_parent != core)
+			continue;
+		tmp_clk = clk_detect_unintended_rate_changes(child, fix);
+		if (tmp_clk)
+			return tmp_clk;
+	}
+
+	if (core->new_child) {
+		tmp_clk = clk_detect_unintended_rate_changes(core->new_child, fix);
+		if (tmp_clk)
+			return tmp_clk;
+	}
+
+	return NULL;
+}
+
 /*
  * Notify about rate changes in a subtree. Always walk down the whole tree
  * so that in case of an error we can walk down the whole tree again and
@@ -2484,6 +2552,21 @@ static int clk_core_set_rate_nolock(struct clk_core *core,
 		goto err;
 	}
 
+	/*
+	 * The notifying process offers the possibility to fix the rates of
+	 * unrelated clocks along the tree. After that, run a detection to find
+	 * clocks which are potentially wrongly configured now. These might be
+	 * fixed by the core in the future.
+	 */
+	fail_clk = clk_detect_unintended_rate_changes(top, false);
+	if (fail_clk) {
+		pr_err("%s: unintended rate change cannot be fixed\n",
+		       fail_clk->name);
+		ret = -EINVAL;
+		goto err;
+	}
+
+
 	/* change the rates */
 	clk_change_rate(top);
 

-- 
2.34.1