linux-kernel - Re: [PATCH v2 6/8] clk: Allow parents to be specified without string names

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Message-ID: <155189453289.20095.9593541968121360874@swboyd.mtv.corp.google.com>
Date:   Wed, 06 Mar 2019 09:48:52 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Jeffrey Hugo <jhugo@...eaurora.org>,
        Michael Turquette <mturquette@...libre.com>
Cc:     linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Russell King <linux@...linux.org.uk>,
        Chen-Yu Tsai <wens@...e.org>
Subject: Re: [PATCH v2 6/8] clk: Allow parents to be specified without string names

Quoting Jeffrey Hugo (2019-03-02 13:25:06)
> On 2/26/2019 3:34 PM, Stephen Boyd wrote:
> > The common clk framework is lacking in ability to describe the clk
> > topology without specifying strings for every possible parent-child
> > link. There are a few drawbacks to the current approach:
> > 
> >   1) String comparisons are used for everything, including describing
> >   topologies that are 'local' to a single clock controller.
> > 
> >   2) clk providers (e.g. i2c clk drivers) need to create globally unique
> >   clk names to avoid collisions in the clk namespace, leading to awkward
> >   name generation code in various clk drivers.
> > 
> >   3) DT bindings may not fully describe the clk topology and linkages
> >   between clk controllers because drivers can easily rely on globally unique
> >   strings to describe connections between clks.
> > 
> > This leads to confusing DT bindings, complicated clk name generation
> > code, and inefficient string comparisons during clk registration just so
> > that the clk framework can detect the topology of the clk tree.
> > Furthermore, some drivers call clk_get() and then __clk_get_name() to
> > extract the globally unique clk name just so they can specify the parent
> > of the clk they're registering. We have of_clk_parent_fill() but that
> > mostly only works for single clks registered from a DT node, which isn't
> > the norm. Let's simplify this all by introducing two new ways of
> > specifying clk parents.
> > 
> > The first method is an array of pointers to clk_hw structures
> > corresponding to the parents at that index. This works for clks that are
> > registered when we have access to all the clk_hw pointers for the
> > parents.
> > 
> > The second method is a mix of clk_hw pointers and strings of local and
> > global parent clk names. If the .name member of the map is set we'll
> > look for that clk by performing a DT based lookup of the device the clk
> > is registered with and the .name specified in the map. If that fails,
> > we'll fallback to the .fallback member and perform a global clk name
> > lookup like we've always done before.
> > 
> > Using either one of these new methods is entirely optional. Existing
> > drivers will continue to work, and they can migrate to this new approach
> > as they see fit. Eventually, we'll want to get rid of the 'parent_names'
> > array in struct clk_init_data and use one of these new methods instead.
> > 
> 
> I don't know exactly what regressed from V1, but this change breaks all 
> clock drivers as far as I can tell.  All clocks from old and new (ie 
> 8998 mmcc rebased onto this) drivers end up as orphans.
> 
> Is there some data I can provide to help you figure out the issue?
> 

Can you try this patch? It fixes a pointer blunder that I'm sad about.

----8<-----
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 37aea7884166..d12afd256dc5 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -3297,15 +3297,17 @@ struct clk *clk_hw_create_clk(struct device *dev, struct clk_hw *hw,
 	return clk;
 }
 
-static int clk_cpy_name(const char *dst, const char *src, bool must_exist)
+static int clk_cpy_name(const char **dst_p, const char *src, bool must_exist)
 {
+	const char *dst;
+
 	if (!src) {
 		if (must_exist)
 			return -EINVAL;
 		return 0;
 	}
 
-	dst = kstrdup_const(src, GFP_KERNEL);
+	*dst_p = dst = kstrdup_const(src, GFP_KERNEL);
 	if (!dst)
 		return -ENOMEM;
 
@@ -3341,14 +3343,14 @@ static int clk_core_populate_parent_map(struct clk_core *core)
 			WARN(!parent_names[i],
 				"%s: invalid NULL in %s's .parent_names\n",
 				__func__, core->name);
-			ret = clk_cpy_name(parent->name, parent_names[i],
+			ret = clk_cpy_name(&parent->name, parent_names[i],
 					   true);
 		} else if (parent_data) {
 			parent->hw = parent_data[i].hw;
-			ret = clk_cpy_name(parent->fw_name,
+			ret = clk_cpy_name(&parent->fw_name,
 					   parent_data[i].fw_name, false);
 			if (!ret)
-				ret = clk_cpy_name(parent->name,
+				ret = clk_cpy_name(&parent->name,
 						   parent_data[i].name,
 						   false);
 		} else if (parent_hws) {