Re: [PATCH v2 2/2] hwrng: hisi: Add support for Hisilicon SoC RNG

[Kefeng Wang <wangkefeng.wang-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>]

On 2016/4/8 22:35, Mathieu Poirier wrote:
> On 7 April 2016 at 20:03, Kefeng Wang <wangkefeng.wang-hv44wF8Li93QT0dZR+AlfA@public.gmane.org> wrote:
>>
>>
>> On 2016/4/7 22:55, Mathieu Poirier wrote:
>>> On 7 April 2016 at 02:23, Kefeng Wang <wangkefeng.wang-hv44wF8Li93QT0dZR+AlfA@public.gmane.org> wrote:
>>>> This adds the Hisilicon Random Number Generator(RNG) support,
>>>> which is found in Hip04 and Hip05 soc.
>>>>
>>>> Signed-off-by: Kefeng Wang <wangkefeng.wang-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
>>>> ---
>>>>  drivers/char/hw_random/Kconfig    |  13 ++++
>>>>  drivers/char/hw_random/Makefile   |   1 +
>>>>  drivers/char/hw_random/hisi-rng.c | 121 ++++++++++++++++++++++++++++++++++++++
>>>>  3 files changed, 135 insertions(+)
>>>>  create mode 100644 drivers/char/hw_random/hisi-rng.c
>> [...]
>>>> +
>>>> +#define RNG_SEED       0x0
>>>> +#define RNG_CTRL       0x4
>>>> +  #define RNG_SEED_SEL BIT(2)
>>>> +  #define RNG_RING_EN  BIT(1)
>>>> +  #define RNG_EN       BIT(0)
>>>> +#define RNG_RAN_NUM    0x10
>>>> +#define RNG_PHY_SEED   0x14
>>>> +#define RNG_RELOAD_ERR 0x84
>>>> +
>>>> +#define to_hisi_rng(p) container_of(p, struct hisi_rng, rng)
>>>> +
>>>> +static int seed_sel;
>>>> +module_param(seed_sel, int, S_IRUGO);
>>>> +MODULE_PARM_DESC(seed_sel, "Auto reload seed. 0, use LFSR(default); 1, use ring oscillator.");
>>>> +
>>>> +struct hisi_rng {
>>>> +       void __iomem *base;
>>>> +       struct hwrng rng;
>>>> +};
>>>> +
>>>> +static int hisi_rng_init(struct hwrng *rng)
>>>> +{
>>>> +       struct hisi_rng *hrng = to_hisi_rng(rng);
>>>> +       int val = RNG_EN;
>>>> +       u32 seed;
>>>> +
>>>> +       /* get a random number as initial seed */
>>>> +       get_random_bytes(&seed, sizeof(seed));
>>>> +
>>>> +       writel_relaxed(seed, hrng->base + RNG_SEED);
>>>> +
>>>> +       if (seed_sel == 1)
>>>> +               val |= RNG_RING_EN | RNG_SEED_SEL;
>>>
>>> Hello Kefeng,
>>>
>>> Please explain what this mode does.  Otherwise reviewers have to make
>>> a guess based on the description of the module parameter.
>> The seed is reload periodically, there are two choice of seeds, default using
>> the val from LFSR, seed_sel = 1  will use the val generated by ring oscillator.
> 
> This is the kind of comment that should be in the code.  That way
> people can understand what is going on.
> 

Ok, will add them into code.

>>>
>>>> +
>>>> +       writel_relaxed(val, hrng->base + RNG_CTRL);
>>>> +       return 0;
>>>> +}
>>>> +
>>>> +static void hisi_rng_cleanup(struct hwrng *rng)
>>>> +{
>>>> +       struct hisi_rng *hrng = to_hisi_rng(rng);
>>>> +
>>>> +       writel_relaxed(0, hrng->base + RNG_CTRL);
>>>> +}
>>>> +
>>>> +static int hisi_rng_read(struct hwrng *rng, void *buf, size_t max,
>>>> +                          bool wait)
>>>
>>> What are variable 'max' and 'wait' used for?  As far as I can tell
>>> they can be removed.
>> Ok, will use data_read callback in struct hwrng.
> 
> Sorry about that, I just noticed this morning the "data_read()"
> callback is obsolete [1].  As such you can probably keep the code the
> way you had it.
> 
> [1]. http://lxr.free-electrons.com/source/include/linux/hw_random.h#L28
> 
>>
>>>
>>>> +{
>>>> +       struct hisi_rng *hrng = to_hisi_rng(rng);
>>>> +       u32 *data = buf;
>>>> +
>>>> +       *data = readl_relaxed(hrng->base + RNG_RAN_NUM);
>>>> +       return 4;
>>>
>>> Why not simply doing the readl_relaxed() in the the code rather than
>>> introducing a new function?
>> Not clear, your mean introduce the data variable?
>> Will use following data_read, thanks.
>>
>> static int hisi_rng_data_read(struct hwrng *rng, u32 *data)
>> {
>>        struct hisi_rng *hrng = to_hisi_rng(rng);
>>        *data = readl_relaxed(hrng->base + RNG_RAN_NUM);
>>        return 4;
>> }
> 
> See my comment above, you were right the first time.

Will resend it, thanks for your review, :)

> 
> Apology and regards,
> Mathieu
> 
>>
>> Thanks,
>> Kefeng
>>
>>
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> 
> .
> 

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