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, [email protected] wrote: >> From: Miaoqing Pan <[email protected]> >> >> 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 <[email protected]> >> --- >> 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 > -- To unsubscribe from this list: send the line "unsubscribe linux-wireless" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
