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SubjectRe: [PATCH v2 6/8] clk: Allow parents to be specified without string names
Date
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) {
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