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

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Date:	Fri, 22 Jun 2012 10:39:45 +0900
From:	jonghwa3.lee@...sung.com
To:	Stephen Boyd <sboyd@...eaurora.org>
Cc:	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>
Subject: Re: [PATCH] Exynos : Add support for Exynos random number generator

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

>>
>>>> +{
>>>> +	int ret;
>>>> +	struct exynos_rng *exynos_rng;
>>>> +	struct resource *res;
>>>> +
>>>> +	exynos_rng = devm_kzalloc(&pdev->dev, sizeof(struct exynos_rng),
>>>> +					GFP_KERNEL);
>>>> +	if (!exynos_rng)
>>>> +		return -ENOMEM;
>>>> +
>>>> +	exynos_rng->dev = &pdev->dev;
>>>> +	exynos_rng->rng.name = "exynos";
>>>> +	exynos_rng->rng.init =	exynos_init;
>>>> +	exynos_rng->rng.read = exynos_read;
>>>> +	exynos_rng->clk = clk_get(NULL, "secss");
>>> Can you please pass &pdev->dev to clk_get()?
>>>
>>
>> But, this clock is not only used in PRNG. Should i put it in?
> 
> Why would that matter? I'm not familiar with the samsung clock
> implementation but I would assume that something like clkdev is being
> used. Ideally you would have one lookup entry per struct device that
> uses this clock and then tie each lookup entry to the same clock. This
> allows you to support multiple instances of the same device in a generic
> way (e.g. two rng devices that use different clocks but from the driver
> perspective they have the same name 'secss').
> 


Okay, I see. I'll apply it.
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