linux-kernel - Re: [RFC,PATCH 1/3] Add a common struct clk

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 15 Feb 2011 14:43:05 +1300
From:	Ryan Mallon <ryan@...ewatersys.com>
To:	Jeremy Kerr <jeremy.kerr@...onical.com>
CC:	linux-arm-kernel@...ts.infradead.org,
	Nicolas Pitre <nicolas.pitre@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-sh@...r.kernel.org,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Paul Mundt <lethal@...ux-sh.org>, linux-kernel@...r.kernel.org,
	Dima Zavin <dmitriyz@...gle.com>,
	Saravana Kannan <skannan@...eaurora.org>,
	Ben Dooks <ben-linux@...ff.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Russell King <linux@....linux.org.uk>
Subject: Re: [RFC,PATCH 1/3] Add a common struct clk

On 02/15/2011 02:36 PM, Jeremy Kerr wrote:
> Hi Ryan,
> 
>>> +int clk_enable(struct clk *clk)
>>> +{
>>> +	unsigned long flags;
>>> +	int ret = 0;
>>> +
>>> +	spin_lock_irqsave(&clk->enable_lock, flags);
>>
>> 	WARN_ON(clk->prepare_count == 0); ?
> 
> Added later, but yes.

Okay, but still failing to understand why this isn't it the first patch.
You are introducing a new file after all.

>>
>>> +	if (clk->enable_count == 0 && clk->ops->enable)
>>> +		ret = clk->ops->enable(clk);
>>
>> Does it make sense to have a clock with no enable function which still
>> returns success from clk_enable? Do we have any platforms which have
>> NULL clk_enable functions?
> 
> It does, yes. Driver code should be always be calling clk_enable before using 
> a clock, regardless of the implementation (which it shouldn't have to care 
> abut), and should abort their initialisation if the clk_enable() fails.
> 
> Some clocks are always running, so the enable op will be empty. This is not an 
> error, so the driver is free to continue.
> 
>> I think that for enable/disable at least we should require platforms to
>> provide functions and oops if they have failed to do so. In the rare
>> case that a platform doesn't need to do anything for enable/disable they
>> can just supply empty functions.
> 
> Sounds like useless boilerplate - it's not an error to not need 
> enable/disable, so I don't see why we need to add extra effort to handle this 
> case.

I have been convinced that enable/prepare potentially being NULL
callbacks is valid :-).

> 
>>> +/**
>>> + * __clk_get - acquire a reference to a clock
>>> + *
>>> + * @clk: The clock to refcount
>>> + *
>>> + * Before a clock is returned from clk_get, this function should be
>>> called + * to update any clock-specific refcounting.
>>
>> This is a bit misleading. It's not "should be called", it "is called". I
>> think you should just remove the documentation for __clk_get/__clk_put
>> or move it into clk.c since the functions are only used internally by
>> the common clock code.
> 
> It'd be nice to remove this from the header, but this means we'll need extern 
> prototypes in clkdev.c. Might be a reasonable compromise though.

That's probably a better approach anyway, since that makes it blatantly
obvious that the __clk_get and __clk_put functions should not be called
from anywhere except clkdev.c.

> 
>>> +/**
>>> + * clk_prepare - prepare clock for atomic enabling.
>>> + *
>>> + * @clk: The clock to prepare
>>> + *
>>> + * Do any blocking initialisation on @clk, allowing the clock to be
>>> later + * enabled atomically (via clk_enable). This function may sleep.
>>
>> "Possibly blocking" as below?
> 
> Yep, will unify these (and spell "possibly" correctly :) )

:-)

~Ryan

-- 
Bluewater Systems Ltd - ARM Technology Solution Centre

Ryan Mallon         		5 Amuri Park, 404 Barbadoes St
ryan@...ewatersys.com         	PO Box 13 889, Christchurch 8013
http://www.bluewatersys.com	New Zealand
Phone: +64 3 3779127		Freecall: Australia 1800 148 751
Fax:   +64 3 3779135			  USA 1800 261 2934
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/