ath9k: feeding entropy in kernel from ADC capture

This patch is derived from
commit 6301566e0b ("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@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>

drivers/net/wireless/ath/ath9k/Kconfig

@@ -176,3 +176,14 @@ config ATH9K_HTC_DEBUGFS
 	depends on ATH9K_HTC && DEBUG_FS
 	---help---
 	  Say Y, if you need access to ath9k_htc's statistics.
+
+config ATH9K_HWRNG
+	bool "Random number generator support"
+	depends on ATH9K && (HW_RANDOM = y || HW_RANDOM = ATH9K)
+	default y
+	---help---
+	  This option incorporates the ADC register output as a source of
+	  randomness into Linux entropy pool (/dev/urandom and /dev/random)
+
+	  Say Y, feeds the entropy directly from the WiFi driver to the input
+	  pool.

drivers/net/wireless/ath/ath9k/Makefile

@@ -15,6 +15,7 @@ ath9k-$(CONFIG_ATH9K_DFS_DEBUGFS) += dfs_debug.o
 ath9k-$(CONFIG_ATH9K_DFS_CERTIFIED) += dfs.o
 ath9k-$(CONFIG_ATH9K_TX99) += tx99.o
 ath9k-$(CONFIG_ATH9K_WOW) += wow.o
+ath9k-$(CONFIG_ATH9K_HWRNG) += rng.o
 
 ath9k-$(CONFIG_ATH9K_DEBUGFS) += debug.o
 

drivers/net/wireless/ath/ath9k/ath9k.h

@@ -23,6 +23,7 @@
 #include <linux/leds.h>
 #include <linux/completion.h>
 #include <linux/time.h>
+#include <linux/hw_random.h>
 
 #include "common.h"
 #include "debug.h"
@@ -1041,6 +1042,11 @@ struct ath_softc {
 	u32 wow_intr_before_sleep;
 	bool force_wow;
 #endif
+
+#ifdef CONFIG_ATH9K_HWRNG
+	u32 rng_last;
+	struct task_struct *rng_task;
+#endif
 };
 
 /********/
@@ -1063,6 +1069,22 @@ static inline int ath9k_tx99_send(struct ath_softc *sc,
 }
 #endif /* CONFIG_ATH9K_TX99 */
 
+/***************************/
+/* Random Number Generator */
+/***************************/
+#ifdef CONFIG_ATH9K_HWRNG
+void ath9k_rng_start(struct ath_softc *sc);
+void ath9k_rng_stop(struct ath_softc *sc);
+#else
+static inline void ath9k_rng_start(struct ath_softc *sc)
+{
+}
+
+static inline void ath9k_rng_stop(struct ath_softc *sc)
+{
+}
+#endif
+
 static inline void ath_read_cachesize(struct ath_common *common, int *csz)
 {
 	common->bus_ops->read_cachesize(common, csz);

drivers/net/wireless/ath/ath9k/main.c

@@ -739,6 +739,8 @@ static int ath9k_start(struct ieee80211_hw *hw)
 
 	ath9k_ps_restore(sc);
 
+	ath9k_rng_start(sc);
+
 	return 0;
 }
 
@@ -828,6 +830,8 @@ static void ath9k_stop(struct ieee80211_hw *hw)
 
 	ath9k_deinit_channel_context(sc);
 
+	ath9k_rng_stop(sc);
+
 	mutex_lock(&sc->mutex);
 
 	ath_cancel_work(sc);

drivers/net/wireless/ath/ath9k/rng.c

@@ -0,0 +1,107 @@
+/*
+ * Copyright (c) 2015 Qualcomm Atheros, Inc.
+ *
+ * Permission to use, copy, modify, and/or distribute this software for any
+ * purpose with or without fee is hereby granted, provided that the above
+ * copyright notice and this permission notice appear in all copies.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+ * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+ * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
+ * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+ * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ */
+
+#include <linux/hw_random.h>
+#include <linux/kthread.h>
+
+#include "ath9k.h"
+#include "hw.h"
+#include "ar9003_phy.h"
+
+#define ATH9K_RNG_BUF_SIZE	320
+#define ATH9K_RNG_ENTROPY(x)	(((x) * 8 * 320) >> 10) /* quality: 320/1024 */
+
+static int ath9k_rng_data_read(struct ath_softc *sc, u32 *buf, u32 buf_size)
+{
+	int i, j;
+	u32  v1, v2, rng_last = sc->rng_last;
+	struct ath_hw *ah = sc->sc_ah;
+
+	ath9k_ps_wakeup(sc);
+
+	REG_RMW_FIELD(ah, AR_PHY_TEST, AR_PHY_TEST_BBB_OBS_SEL, 1);
+	REG_CLR_BIT(ah, AR_PHY_TEST, AR_PHY_TEST_RX_OBS_SEL_BIT5);
+	REG_RMW_FIELD(ah, AR_PHY_TEST_CTL_STATUS, AR_PHY_TEST_CTL_RX_OBS_SEL, 0);
+
+	for (i = 0, j = 0; i < buf_size; i++) {
+		v1 = REG_READ(ah, AR_PHY_TST_ADC) & 0xffff;
+		v2 = REG_READ(ah, AR_PHY_TST_ADC) & 0xffff;
+
+		/* wait for data ready */
+		if (v1 && v2 && rng_last != v1 && v1 != v2 && v1 != 0xffff &&
+		    v2 != 0xffff)
+			buf[j++] = (v1 << 16) | v2;
+
+		rng_last = v2;
+	}
+
+	ath9k_ps_restore(sc);
+
+	sc->rng_last = rng_last;
+
+	return j << 2;
+}
+
+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 (unlikely(!bytes_read)) {
+			msleep_interruptible(10);
+			continue;
+		}
+
+		/* sleep until entropy bits under write_wakeup_threshold */
+		add_hwgenerator_randomness((void *)rng_buf, bytes_read,
+					   ATH9K_RNG_ENTROPY(bytes_read));
+	}
+
+	kfree(rng_buf);
+out:
+	sc->rng_task = NULL;
+
+	return 0;
+}
+
+void ath9k_rng_start(struct ath_softc *sc)
+{
+	struct ath_hw *ah = sc->sc_ah;
+
+	if (sc->rng_task)
+		return;
+
+	if (!AR_SREV_9300_20_OR_LATER(ah))
+		return;
+
+	sc->rng_task = kthread_run(ath9k_rng_kthread, sc, "ath9k-hwrng");
+	if (IS_ERR(sc->rng_task))
+		sc->rng_task = NULL;
+}
+
+void ath9k_rng_stop(struct ath_softc *sc)
+{
+	if (sc->rng_task)
+		kthread_stop(sc->rng_task);
+}