Date: Sat, 12 Jul 2008 23:48:23 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: Dmitry Baryshkov <dbaryshkov@gmail.com>
Cc: linux-kernel@vger.kernel.org,
       Haavard Skinnemoen <haavard.skinnemoen@atmel.com>,
       Russell King <rmk+lkml@arm.linux.org.uk>,
       Paul Mundt <lethal@linux-sh.org>,
       pHilipp Zabel <philipp.zabel@gmail.com>, Pavel Machek <pavel@ucw.cz>,
       tony@atomide.com, paul@pwsan.com, David Brownell <david-b@pacbell.net>,
       Mark Brown <broonie@opensource.wolfsonmicro.com>, ian <spyro@f2s.com>
Subject: Re: [PATCH 1/3] genclk: add generic framework for managing clocks.
Message-Id: <20080712234823.e632c7f9.akpm@linux-foundation.org>
In-Reply-To: <20080708134336.GA6240@doriath.ww600.siemens.net>
References: <20080708134242.GA6176@doriath.ww600.siemens.net>
	<20080708134336.GA6240@doriath.ww600.siemens.net>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 6644
Lines: 273

On Tue, 8 Jul 2008 17:43:36 +0400 Dmitry Baryshkov <dbaryshkov@gmail.com> wrote:

> Provide a generic framework that platform may choose
> to support clocks api. In particular this provides
> platform-independant struct clk definition, a full
> implementation of clocks api and a set of functions
> for registering and unregistering clocks in a safe way.
> 

So I'll merge this into -mm and, unless there be suitably-serious
objections, into 2.6.27.

The other two patches got rejects all over the place - so many that I
didn't even attempt to fix them.  Perhaps you were developing againt
Linus's tree, which really is not a successful strategy late in the
-rc's.

>
> ...
>
> +struct clk_priv {
> +	struct list_head node;
> +#ifdef CONFIG_DEBUG_SPINLOCK
> +	struct lock_class_key lock_key;
> +#endif

hm, what's this unusual-but-uncommented code doing in here?  Please
always comment unusual code.

There is already a zero-byte version of `struct lock_class_key' in
include/linux/lockdep.h, dependent upon CONFIG_LOCKDEP.

Methinks some explanation and fixing is needed here.

>
> ...
>
> +#include "genclk.h"
> +
> +LIST_HEAD(clocks);

whoa.  We have a kernel-wide symbol called "locks"?

afaict that won't cause any linkage errors, but those compilation units
which already have static variables called "clocks" will explode if
they deliberately or accidentally include your header file.

I suggest that this be renamed to something more subsystem-specific. 
genclk_clocks?

Or, better, refactor the code a bit and make it static.  Do other
compilation units _really_ need to go poking into genclk's internals? 
Would it be better to always access this data structure via API calls?

> +DEFINE_SPINLOCK(clocks_lock);

genclk_clocks_lock.

> +static int clk_can_get_def(struct clk *clk, struct device *dev)
> +{
> +	return 1;
> +}
> +
> +static unsigned long clk_get_rate_def(struct clk *clk)
> +{
> +	return 0;
> +}
> +
> +static long clk_round_rate_def(struct clk *clk, unsigned long hz, bool apply)
> +{
> +	long rate = clk->ops->get_rate(clk);
> +
> +	if (apply && hz != rate)
> +		return -EINVAL;
> +
> +	return rate;
> +}
> +
> +static void clk_release(struct kref *ref)
> +{
> +	struct clk *clk = container_of(ref, struct clk, priv.ref);
> +
> +	BUG_ON(!clk->release);
> +
> +	if (clk->parent)
> +		kref_get(&clk->parent->priv.ref);
> +
> +	clk->release(clk);
> +}
> +EXPORT_SYMBOL(clk_round_rate);

This export is in the wrong place.

> +struct clk* clk_get_parent(struct clk *clk)

checkpatch.pl, please.

> +{
> +	struct clk *parent;
> +
> +	spin_lock(&clk->priv.lock);
> +
> +	parent = clk->parent;
> +	kref_get(&parent->priv.ref);
> +
> +	spin_unlock(&clk->priv.lock);
> +
> +	return parent;
> +}
> +EXPORT_SYMBOL(clk_get_parent);

As this is a new kernel-wide utility library, it is appropriate that
all of its public interfaces (at least) be documented.  An appropriate
way of doing that is via kerneldoc annotation.  Please don't forget to
document return values and call environment prerequisites (eg: requires
foo_lock, may be called from interrupt context, etc, etc).

> +int clk_set_parent(struct clk *clk, struct clk *parent)
> +{
> +	int rc = -EINVAL;
> +	struct clk *old;
> +
> +	spin_lock(&clk->priv.lock);
> +
> +	if (!clk->ops->set_parent)
> +		goto out;
> +
> +	old = clk->parent;
> +
> +	rc = clk->ops->set_parent(clk, parent);
> +	if (rc)
> +		goto out;
> +
> +	kref_get(&parent->priv.ref);
> +	clk->parent = parent;
> +
> +	clk_debugfs_reparent(clk, old, parent);
> +
> +	kref_put(&old->priv.ref, clk_release);
> +
> +out:
> +	spin_unlock(&clk->priv.lock);
> +
> +	return rc;
> +}
> +EXPORT_SYMBOL(clk_set_parent);
> +
> +int clk_register(struct clk *clk)
> +{
> +	int rc;
> +
> +	BUG_ON(!clk->ops);
> +	BUG_ON(!clk->ops->enable || !clk->ops->disable);
> +
> +	if (!clk->ops->can_get)
> +		clk->ops->can_get = clk_can_get_def;
> +	if (!clk->ops->get_rate)
> +		clk->ops->get_rate = clk_get_rate_def;
> +	if (!clk->ops->round_rate)
> +		clk->ops->round_rate = clk_round_rate_def;
> +
> +	kref_init(&clk->priv.ref);
> +#ifdef CONFIG_DEBUG_SPINLOCK
> +	__spin_lock_init(&clk->priv.lock, "&clk->priv.lock", &clk->priv.lock_key);
> +#else
> +	spin_lock_init(&clk->priv.lock);
> +#endif

Something's wrong here, I suspect.

> +	spin_lock(&clocks_lock);
> +	if (clk->parent)
> +		kref_get(&clk->parent->priv.ref);
> +	list_add_tail(&clk->priv.node, &clocks);
> +
> +	rc = clk_debugfs_init(clk);
> +	if (rc) {
> +		list_del(&clk->priv.node);
> +		kref_put(&clk->priv.ref, clk_release);
> +	}
> +
> +	spin_unlock(&clocks_lock);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(clk_register);
> +
> +void clk_unregister(struct clk *clk)
> +{
> +	spin_lock(&clocks_lock);
> +	clk_debugfs_clean(clk);

can't call debugfs_remove() under spinlock.

> +	list_del(&clk->priv.node);
> +	kref_put(&clk->priv.ref, clk_release);

Might not be able to call kref_put(), either.

> +	spin_unlock(&clocks_lock);
> +}
> +EXPORT_SYMBOL(clk_unregister);

Please always test code with all kernel debug options enabled.  See
Documentation/SubmitChecklist.

>
> ...
>
> +int clk_debugfs_init(struct clk *clk)
> +{
> +	struct dentry *dir;
> +	struct dentry *info;
> +
> +	/*
> +	 * We initialise it here, because this call can be executed from within arch code,
> +	 * so specifyint correct initialisation place is a bit tricky
> +	 */
> +	if (!clkdir)
> +		clkdir = debugfs_create_dir("clocks", NULL);

Missed a check for debugfs_create_dir() failure.

> +	dir = debugfs_create_dir(clk->name,
> +			clk->parent ? clk->parent->dir : clkdir);
> +
> +	if (IS_ERR(dir))
> +		return PTR_ERR(dir);
> +
> +	info = debugfs_create_file("info", S_IFREG | S_IRUGO,
> +			dir, clk, &genclk_operations);
> +
> +	if (IS_ERR(info)) {
> +		debugfs_remove(dir);
> +		return PTR_ERR(info);
> +	}
> +
> +	clk->dir = dir;
> +	clk->priv.info = info;
> +
> +	return 0;
> +}
> +
>
> ...
>
> +void clk_debugfs_reparent(struct clk *clk, struct clk *old, struct clk *new)
> +{
> +	struct dentry *oldd = old ? old->dir : clkdir;
> +	struct dentry *newd = new ? new->dir : clkdir;
> +	struct dentry *dir = debugfs_rename(oldd, clk->dir, newd, clk->name);
> +
> +	if (IS_ERR(dir))
> +		WARN_ON(1);
> +	else
> +		clk->dir = dir;
> +}

Could do

	if (!WARN_ON(IS_ERR(dir)))
		clk->dir = dir;

Or not.  What you have there is clearer.

Quite a bit of rework is needed here and it needs to be fully retested. 
I won't apply it after all.

--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/