Thanks Felix. You mentioned 'Polling every 10 milliseconds' is not right,
the kthread will always sleep until when the condition
'ENTROPY_BITS(&input_pool) <=
random_write_wakeup_bits'(add_hwgenerator_randomness()) is true. And
ath9k_rng_data_read() almost w/o failure, I will add unlikely in patch v3.
- Miaoqing
> On 2015-09-30 05:09, miaoqing@xxxxxxxxxxxxxx wrote:
>> From: Miaoqing Pan <miaoqing@xxxxxxxxxxxxxx>
>>
>> This patch is derived from
>> commit 6301566e0b2d ("ath9k: export HW random number generator"),
>>
>> We evaluated the entropy of the ADC data on QCA9531, QCA9561, QCA955x,
>> and AR9340, and it has sufficient quality random data (at least 10 bits
>> and up to 22 bits of min-entropy for a 32-bit value). We conservatively
>> assume the min-entropy is 10 bits out of 32 bits. Thus,
>> ATH9K_RNG_BUF_SIZE
>> is set to 320 (u32) i.e., 1.25 kilobytes of data is inserted to fill up
>> the pool as soon as the entropy counter becomes 896/4096 (set by
>> random.c).
>> Since ADC was not designed to be a dedicated HW RNG, we do not want to
>> bind
>> it to /dev/hwrng framework directly. This patch feeds the entropy
>> directly
>> from the WiFi driver to the input pool. The ADC register output is only
>> used as a seed for the Linux entropy pool. No conditioning is needed,
>> since all the conditioning is performed by the pool itself.
>>
>> Signed-off-by: Miaoqing Pan <miaoqing@xxxxxxxxxxxxxx>
>> ---
>> drivers/net/wireless/ath/ath9k/Kconfig | 11 ++++
>> drivers/net/wireless/ath/ath9k/Makefile | 1 +
>> drivers/net/wireless/ath/ath9k/ath9k.h | 22 +++++++
>> drivers/net/wireless/ath/ath9k/main.c | 4 ++
>> drivers/net/wireless/ath/ath9k/rng.c | 106
>> ++++++++++++++++++++++++++++++++
>> 5 files changed, 144 insertions(+)
>> create mode 100644 drivers/net/wireless/ath/ath9k/rng.c
>>
>
>> diff --git a/drivers/net/wireless/ath/ath9k/rng.c
>> b/drivers/net/wireless/ath/ath9k/rng.c
>> new file mode 100644
>> index 0000000..93a7485
>> --- /dev/null
>> +++ b/drivers/net/wireless/ath/ath9k/rng.c
>> [...]
>> +static int ath9k_rng_kthread(void *data)
>> +{
>> + int bytes_read;
>> + struct ath_softc *sc = data;
>> + u32 *rng_buf;
>> +
>> + rng_buf = kmalloc_array(ATH9K_RNG_BUF_SIZE, sizeof(u32), GFP_KERNEL);
>> + if (!rng_buf)
>> + goto out;
>> +
>> + while (!kthread_should_stop()) {
>> + bytes_read = ath9k_rng_data_read(sc, rng_buf,
>> + ATH9K_RNG_BUF_SIZE);
>> + if (!bytes_read) {
>> + msleep_interruptible(10);
>> + continue;
>> + }
>> +
>> + add_hwgenerator_randomness((void *)rng_buf, bytes_read,
>> + ATH9K_RNG_ENTROPY(bytes_read));
> Polling every 10 milliseconds seems a bit excessive to me. Think about
> all those useless wakeups per second that this will produce on battery
> powered devices.
> How about polling more data without sleeping when the thread starts, and
> then afterwards only poll once every few seconds?
>
> - Felix
>
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