linux-kernel - Re: [PATCH] Exynos : Add support for Exynos random number generator

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Date:	Wed, 27 Jun 2012 10:03:16 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Stephen Boyd <sboyd@...eaurora.org>
cc:	jonghwa3.lee@...sung.com, <linux-kernel@...r.kernel.org>,
	Matt Mackall <mpm@...enic.com>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Julia Lawall <Julia.Lawall@...6.fr>,
	Jamie Iles <jamie@...ieiles.com>,
	Kyungmin Park <kyungmin.park@...sung.com>,
	Linux PM mailing list <linux-pm@...r.kernel.org>
Subject: Re: [PATCH] Exynos : Add support for Exynos random number generator

On Tue, 26 Jun 2012, Stephen Boyd wrote:

> On 06/21/12 18:39, jonghwa3.lee@...sung.com wrote:
> > On 2012년 06월 21일 12:12, Stephen Boyd wrote:
> >
> >> On 06/20/12 19:39, jonghwa3.lee@...sung.com wrote:
> >>>>> +static int exynos_init(struct hwrng *rng)
> >>>>> +{
> >>>>> +	struct exynos_rng *exynos_rng = container_of(rng,
> >>>>> +						struct exynos_rng, rng);
> >>>>> +	int i;
> >>>>> +	int ret = 0;
> >>>>> +	u32 PRND_SEED[5];
> >>>>> +
> >>>>> +	pm_runtime_put_noidle(exynos_rng->dev);
> >>>>> +	pm_runtime_get_sync(exynos_rng->dev);
> >>>> This looks very odd. Why are you calling pm_runtime_put_noidle()?
> >>>>
> >>> When this callback function is called, the status of power state is
> >>> 'suspended' and use_count is 1.

That's strange to begin with.  If the usage counter is > 0 then the
device shouldn't be suspended.  How does this happen?

>  To perform pm_runtime_get_sync()
> >>> correctly, it requires to have 'suspended' status and use_count is 0.

That's not true.  pm_runtime_get_sync works perfectly well when the 
status is "suspended" and the usage counter is > 0.

> >>> Thus i force to decrease use_count only with using
> >>> pm_runtime_put_noidle. I know it looks odd, but i couldn't find better
> >>> way. Otherwise it can use clk_enable() directly, but i think that it
> >>> isn't good neither.
> >> Is the device suspended initially at probe? If so can you set the state
> >> of the device to suspended?
> >>
> >
> > Yes, it suspended already at the initial of probing. But i can't get
> > your point, you want to me to make device suspended?
> 
> I mean to say you should probably call pm_runtime_set_suspended() during
> probe. But I'm not sure and I would defer to people more familiar with
> runtime pm.

If the device starts out in a suspended state then the subsystem or 
driver should call pm_runtime_set_suspended before calling 
pm_runtime_enable.

Alan Stern

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