Message-ID: <530B8627.4020705@free-electrons.com>
Date:	Mon, 24 Feb 2014 18:49:27 +0100
From:	Gregory CLEMENT <gregory.clement@...e-electrons.com>
To:	Tomasz Figa <tomasz.figa@...il.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 v2] clk: respect the clock dependencies in of_clk_init

Hi Tomasz,

On 23/02/2014 19:46, Tomasz Figa wrote:
> Hi Gregory,
> 
> On 10.02.2014 18:42, 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.
> 
> In general this is really great. It's a first step towards sorting out 
> dependencies between clock providers correctly. I have some comments 
> inline, though.
> 
>>
>> The strict dependency check (all parents of a given clk must be
>> initialized) was added by Boris BREZILLON
> 
> Shouldn't this be reflected by a tag of this patch? If you squash a 
> patch signed off by someone then I believe their sign-off tag should be 
> added to the base patch. Correct me if I'm wrong, though.

It was not really obvious for me to know how to deal with code merged from
someone else, but indeed adding a sign-off tag seems to be sensible.

> 
>>
>> Signed-off-by: Gregory CLEMENT <gregory.clement@...e-electrons.com>
>> ---
>>
>> Since the v1, I have merged the  strict dependency check from Boris.
>> And of course tested on my Armada 370 and Armada XP based board
>>
>>   drivers/clk/clk.c | 109 ++++++++++++++++++++++++++++++++++++++++++++++++++++--
>>   1 file changed, 106 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
>> index 5517944495d8..684976993297 100644
>> --- a/drivers/clk/clk.c
>> +++ b/drivers/clk/clk.c
>> @@ -2526,24 +2526,127 @@ const char *of_clk_get_parent_name(struct device_node *np, int index)
>>   }
>>   EXPORT_SYMBOL_GPL(of_clk_get_parent_name);
>>
>> +struct clock_provider {
> 
> The name is a bit too generic and slightly misleading. IMHO struct 
> deferred_clk_provider (and deferred_clk_providers for the list) would be 
> better.

right

> 
>> +	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;
>> +	int num_parents;
>> +	bool found;
>> +	int i;
>> +
>> +	/*
>> +	 * If there is no clock parent, no need to wait for them, then
>> +	 * we can consider their absence as being ready
>> +	 */
>> +	num_parents = of_count_phandle_with_args(np, "clocks", "#clock-cells");
>> +	if (num_parents <= 0)
>> +		return 1;
> 
> of_clk_get_parent_count() can be used here...

right

> 
>> +
>> +	for (i = 0; i < num_parents; i++) {
>> +		if (of_parse_phandle_with_args(np, "clocks", "#clock-cells", i,
>> +					       &clkspec))
>> +			return 1;
>> +
>> +		/* Check if we have such a provider in our array */
>> +		found = false;
>> +		list_for_each_entry(provider, &of_clk_providers, link) {
>> +			if (provider->node == clkspec.np) {
>> +				found = true;
>> +				break;
>> +			}
>> +		}
>> +
>> +		if (!found)
>> +			return 0;
>> +	}
> 
> ...or even better, __of_clk_get_from_provider() could modified to return
> -EPROBE_DEFER if requested provider is not registered and you could 

There is already a patch sent for this "clk: return probe defer when DT clock
not yet ready": http://article.gmane.org/gmane.linux.kernel/1643466

Mike will you take it?

Then I can use it to implement the suggestion made by Tomasz.

> simply call of_clk_get(np, i) and handle its return value appropriately:
> 
> - on !IS_ERR(clk) call clk_put() and continue with iterations,
> - on IS_ERR(clk) && PTR_ERR(clk) == -EPROBE_DEFER return 0 immediately,
> - in any other case end the loop (end of clock specifiers).

So here we make the assumption that the device tree is written correctly. I think
it should be acceptable because here we only try to deal with the order
of the clocks providers not the accuracy of the device tree. If the device
tree is wrong then it should trig errors message in other part of the kernel.

> 
> This would make CCF even closer to proper handling of provider ordering, 
> with a nice side effect of handling deferred probe for platform devices.
> 
>> +
>> +	return 1;
>> +}
>> +
>>   /**
>>    * 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);
>> +		}
>> +	}
> 
> I wonder if this couldn't be replaced with simply adding all the 
> providers to the list first and then proceeding with the loop below to 
> handle the registrations.

Yes you're right

> 
>> +
>> +	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);
> 
> Hmm, this is basically the code above repeated without the if. What 
> about something like the code snippet below?
> 
> bool force = false;
> while (!list_empty(&clk_provider_list)) {
> 	is_init_done = false;
> 	list_for_each_entry_safe(clk_provider, next,
> 				&clk_provider_list, node) {
> 		if (force || 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)
> 		force = true;
> }

indeed it's better.


Thanks for your review,

Gregory


> 
> Best regards,
> Tomasz
> 


-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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