Date:	Wed, 05 Feb 2014 09:45:16 +0100
From:	Boris BREZILLON <b.brezillon@...rkiz.com>
To:	Gregory CLEMENT <gregory.clement@...e-electrons.com>,
	Mike Turquette <mturquette@...aro.org>
CC:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Andrew Lunn <andrew@...n.ch>,
	Jason Cooper <jason@...edaemon.net>,
	linux-kernel@...r.kernel.org,
	Ezequiel Garcia <ezequiel.garcia@...e-electrons.com>,
	linux-arm-kernel@...ts.infradead.org,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH] clk: respect the clock dependencies in of_clk_init

Hi Greg,

On 04/02/2014 23:59, Gregory CLEMENT wrote:
> Until now the clock providers were initialized in the order found in
> the device tree. This led to have the dependencies between the clocks
> not respected: children clocks could be initialized before their
> parent clocks.
>
> Instead of forcing each platform to manage its own initialization order,
> this patch adds this work inside the framework itself.
>
> Using the data of the device tree the of_clk_init function now delayed
> the initialization of a clock provider if its parent provider was not
> ready yet.
>

Great! I remember having some trouble with this "parent is not 
registered yet" issue (but I don't recall how I solved it, maybe in 
reordering clk nodes).
Anyway, this will help other platforms too (at least the at91 one).

> Signed-off-by: Gregory CLEMENT <gregory.clement@...e-electrons.com>
> ---
> Mike,
>
> this patch could solve the issues we get on severals mvebu platform
> since 3.14-rc1. This is an alternate solution of the patch set sent by
> Sebastian. However as it modifies the clock framework itself, it is
> more sensible.
>
> I find this solution more elegant than changing the order of the
> initialization of the clock at the platform level. However as it
> should be tested on more platforms that only the mvebu ones, it would
> take some time, and I don't want to still have "broken" platform
> during more release candidate. So at the end this patch should be part
> of the 3.15 kernel.
>
> Thanks,
>
> Gregory
>
>   drivers/clk/clk.c | 94 +++++++++++++++++++++++++++++++++++++++++++++++++++++--
>   1 file changed, 91 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> index 5517944495d8..beb0f8b0c2a0 100644
> --- a/drivers/clk/clk.c
> +++ b/drivers/clk/clk.c
> @@ -2526,24 +2526,112 @@ const char *of_clk_get_parent_name(struct device_node *np, int index)
>   }
>   EXPORT_SYMBOL_GPL(of_clk_get_parent_name);
>
> +struct clock_provider {
> +	of_clk_init_cb_t clk_init_cb;
> +	struct device_node *np;
> +	struct list_head node;
> +};
> +
> +static LIST_HEAD(clk_provider_list);
> +
> +/*
> + * This function looks for a parent clock. If there is one, then it
> + * checks that the provider for this parent clock was initialized, in
> + * this case the parent clock will be ready.
> + */
> +static int parent_ready(struct device_node *np)
> +{
> +	struct of_phandle_args clkspec;
> +	struct of_clk_provider *provider;
> +
> +	/*
> +	 * If there is no clock parent, no need to wait for them, then
> +	 * we can consider their absence as being ready
> +	 */
> +	if (of_parse_phandle_with_args(np, "clocks", "#clock-cells", 0,
> +					&clkspec))
> +		return 1;
> +
> +	/* Check if we have such a provider in our array */
> +	list_for_each_entry(provider, &of_clk_providers, link) {
> +		if (provider->node == clkspec.np)
> +			return 1;
> +	}

Shouldn't we wait for all parents to be ready (If I'm right, you're only 
waiting for the first parent...) ?
And if you only request for one clk to be ready, why the first one (you 
could loop over parent clks and stop when one of its parent is ready) ?

Best Regards,

Boris

> +
> +	return 0;
> +}
> +
>   /**
>    * of_clk_init() - Scan and init clock providers from the DT
>    * @matches: array of compatible values and init functions for providers.
>    *
> - * This function scans the device tree for matching clock providers and
> - * calls their initialization functions
> + * This function scans the device tree for matching clock providers
> + * and calls their initialization functions. It also do it by trying
> + * to follow the dependencies.
>    */
>   void __init of_clk_init(const struct of_device_id *matches)
>   {
>   	const struct of_device_id *match;
>   	struct device_node *np;
> +	struct clock_provider *clk_provider, *next;
> +	bool is_init_done;
>
>   	if (!matches)
>   		matches = &__clk_of_table;
>
>   	for_each_matching_node_and_match(np, matches, &match) {
>   		of_clk_init_cb_t clk_init_cb = match->data;
> -		clk_init_cb(np);
> +
> +
> +		if (parent_ready(np)) {
> +			/*
> +			 * The parent clock is ready or there is no
> +			 * clock parent at all, in this case the
> +			 * provider can be initialize immediately.
> +			 */
> +			clk_init_cb(np);
> +		} else {
> +			/*
> +			 * The parent clock is not ready, this
> +			 * provider is moved to a list to be
> +			 * initialized later
> +			 */
> +			struct clock_provider *parent = kzalloc(sizeof(struct clock_provider),
> +							GFP_KERNEL);
> +
> +			parent->clk_init_cb = match->data;
> +			parent->np = np;
> +			list_add(&parent->node, &clk_provider_list);
> +		}
> +	}
> +
> +	while (!list_empty(&clk_provider_list)) {
> +		is_init_done = false;
> +		list_for_each_entry_safe(clk_provider, next,
> +					&clk_provider_list, node) {
> +			if (parent_ready(clk_provider->np)) {
> +				clk_provider->clk_init_cb(clk_provider->np);
> +				list_del(&clk_provider->node);
> +				kfree(clk_provider);
> +				is_init_done = true;
> +			}
> +		}
> +
> +		if (!is_init_done) {
> +			/*
> +			 * We didn't managed to initialize any of the
> +			 * remaining providers during the last loop,
> +			 * so now we initialize all the remaining ones
> +			 * unconditionally in case the clock parent
> +			 * was not mandatory
> +			 */
> +			list_for_each_entry_safe(clk_provider, next,
> +						&clk_provider_list, node) {
> +				clk_provider->clk_init_cb(clk_provider->np);
> +				list_del(&clk_provider->node);
> +				kfree(clk_provider);
> +			}
> +		}
>   	}
>   }
>   #endif
>

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