[RFC PATCH] clk: flatten clk tree in debugfs

[Peter De Schrijver]

This patch flattens the clk tree in CCF debugfs. Instead of representing the
clocks and their hierarchy as a directory structure under
/sys/kernel/debug/clk, each clock gets a single directory directly under
/sys/kernel/debug/clk.

While this may seem strange, here's way I think this is the right thing to do:

1) a directory structure cannot be 'snapshotted' atomically, therefore it's
   not in general possible to get a consistent view of the clocktree, because
   clocks can be reparented at any time. This was solved by adding clk_dump
   and clk_summary, which do guarantee an atomic snapshot of the tree.
   Therefore I think the directory structure doesn't add any value.

2) When writing userspace programs which use the files in the clock
   directories (eg. for testing purposes), it's impossible to know for sure
   where a certain clock will be, because it might have been reparented by the
   time you figured out the path from clk_dump. This makes writing such
   programs more difficult than it should be.

So because the directory structure doesn't give any information we don't
already provide by other means and it makes certain usecases more difficult
than the should be, I think we should move to a flat directory containing
one subdir per clock.

Signed-off-by: Peter De Schrijver <pdeschrijver at nvidia.com>
---
 drivers/clk/clk.c |   54 +++-------------------------------------------------
 1 files changed, 4 insertions(+), 50 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index dff0373..53c6b4f 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -306,7 +306,7 @@ static int clk_debug_create_subtree(struct clk *clk, struct dentry *pdentry)
 		goto out;
 
 	hlist_for_each_entry(child, &clk->children, child_node)
-		clk_debug_create_subtree(child, clk->dentry);
+		clk_debug_create_subtree(child, pdentry);
 
 	ret = 0;
 out:
@@ -326,29 +326,20 @@ out:
  */
 static int clk_debug_register(struct clk *clk)
 {
-	struct clk *parent;
 	struct dentry *pdentry;
 	int ret = 0;
 
 	if (!inited)
 		goto out;
 
-	parent = clk->parent;
-
 	/*
 	 * Check to see if a clk is a root clk.  Also check that it is
 	 * safe to add this clk to debugfs
 	 */
-	if (!parent)
-		if (clk->flags & CLK_IS_ROOT)
-			pdentry = rootdir;
-		else
-			pdentry = orphandir;
+	if (clk->flags & CLK_IS_ROOT)
+		pdentry = rootdir;
 	else
-		if (parent->dentry)
-			pdentry = parent->dentry;
-		else
-			goto out;
+		pdentry = orphandir;
 
 	ret = clk_debug_create_subtree(clk, pdentry);
 
@@ -372,39 +363,6 @@ static void clk_debug_unregister(struct clk *clk)
 }
 
 /**
- * clk_debug_reparent - reparent clk node in the debugfs clk tree
- * @clk: the clk being reparented
- * @new_parent: the new clk parent, may be NULL
- *
- * Rename clk entry in the debugfs clk tree if debugfs has been
- * initialized.  Otherwise it bails out early since the debugfs clk tree
- * will be created lazily by clk_debug_init as part of a late_initcall.
- *
- * Caller must hold prepare_lock.
- */
-static void clk_debug_reparent(struct clk *clk, struct clk *new_parent)
-{
-	struct dentry *d;
-	struct dentry *new_parent_d;
-
-	if (!inited)
-		return;
-
-	if (new_parent)
-		new_parent_d = new_parent->dentry;
-	else
-		new_parent_d = orphandir;
-
-	d = debugfs_rename(clk->dentry->d_parent, clk->dentry,
-			new_parent_d, clk->name);
-	if (d)
-		clk->dentry = d;
-	else
-		pr_debug("%s: failed to rename debugfs entry for %s\n",
-				__func__, clk->name);
-}
-
-/**
  * clk_debug_init - lazily create the debugfs clk tree visualization
  *
  * clks are often initialized very early during boot before memory can
@@ -1277,9 +1235,6 @@ static void __clk_set_parent_after(struct clk *clk, struct clk *parent,
 		clk_disable(old_parent);
 		__clk_unprepare(old_parent);
 	}
-
-	/* update debugfs with new clk tree topology */
-	clk_debug_reparent(clk, parent);
 }
 
 static int __clk_set_parent(struct clk *clk, struct clk *parent, u8 p_index)
@@ -1685,7 +1640,6 @@ out:
 void __clk_reparent(struct clk *clk, struct clk *new_parent)
 {
 	clk_reparent(clk, new_parent);
-	clk_debug_reparent(clk, new_parent);
 	__clk_recalc_accuracies(clk);
 	__clk_recalc_rates(clk, POST_RATE_CHANGE);
 }
-- 
1.7.7.rc0.72.g4b5ea.dirty