linux-kernel - [RFC] clk: Remove cached cores in parent map during unregister

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Message-Id: <20190723051446.20013-1-bjorn.andersson@linaro.org>
Date:   Mon, 22 Jul 2019 22:14:46 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>
Cc:     linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, Rob Clark <robclark@...il.com>,
        Sean Paul <seanpaul@...omium.org>
Subject: [RFC] clk: Remove cached cores in parent map during unregister

As clocks are registered their parents are resolved and the parent_map
is updated to cache the clk_core objects of each existing parent.
But in the event of a clock being unregistered this cache will carry
dangling pointers if not invalidated, so do this for all children of the
clock being unregistered.

Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
---

This resolves the issue seen where the DSI PLL (and it's provided clocks) is
being registered and unregistered multiple times due to probe deferral.

Marking it RFC because I don't fully understand the life of the clock yet.

 drivers/clk/clk.c | 18 +++++++++++++++---
 1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index c0990703ce54..8cd1ad977c50 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -2423,11 +2423,14 @@ bool clk_has_parent(struct clk *clk, struct clk *parent)
 EXPORT_SYMBOL_GPL(clk_has_parent);
 
 static int clk_core_set_parent_nolock(struct clk_core *core,
-				      struct clk_core *parent)
+				      struct clk_core *parent,
+				      bool invalidate_parent)
 {
+	struct clk_core *old_parent = core->parent;
 	int ret = 0;
 	int p_index = 0;
 	unsigned long p_rate = 0;
+	int i;
 
 	lockdep_assert_held(&prepare_lock);
 
@@ -2481,6 +2484,14 @@ static int clk_core_set_parent_nolock(struct clk_core *core,
 		__clk_recalc_accuracies(core);
 	}
 
+	/* invalidate the parent cache */
+	if (!parent && invalidate_parent) {
+		for (i = 0; i < core->num_parents; i++) {
+			if (core->parents[i].core == old_parent)
+				core->parents[i].core = NULL;
+		}
+	}
+
 runtime_put:
 	clk_pm_runtime_put(core);
 
@@ -2517,7 +2528,8 @@ int clk_set_parent(struct clk *clk, struct clk *parent)
 		clk_core_rate_unprotect(clk->core);
 
 	ret = clk_core_set_parent_nolock(clk->core,
-					 parent ? parent->core : NULL);
+					 parent ? parent->core : NULL,
+					 false);
 
 	if (clk->exclusive_count)
 		clk_core_rate_protect(clk->core);
@@ -3772,7 +3784,7 @@ void clk_unregister(struct clk *clk)
 		/* Reparent all children to the orphan list. */
 		hlist_for_each_entry_safe(child, t, &clk->core->children,
 					  child_node)
-			clk_core_set_parent_nolock(child, NULL);
+			clk_core_set_parent_nolock(child, NULL, true);
 	}
 
 	hlist_del_init(&clk->core->child_node);
-- 
2.18.0