carl9170: export HW random number generator

All AR9170 hardware have a 16-Bit random number generator.
The documentation claims the values are suitable for
"security keys".

The "throughput" is around 320Kibit/s. It's slow, but it
does work without introducing any special offload
firmware commands.

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

3 files changed, 139 insertions, 0 deletions

diff --git a/drivers/net/wireless/ath/carl9170/Kconfig b/drivers/net/wireless/ath/carl9170/Kconfig
index 2d1b821b440..267d5dcf82d 100644
--- a/drivers/net/wireless/ath/carl9170/Kconfig
+++ b/drivers/net/wireless/ath/carl9170/Kconfig
@@ -39,3 +39,17 @@ config CARL9170_WPC
         bool
         depends on CARL9170 && (INPUT = y || INPUT = CARL9170)
         default y
+
+config CARL9170_HWRNG
+        bool "Random number generator"
+        depends on CARL9170 && (HW_RANDOM = y || HW_RANDOM = CARL9170)
+        default n
+        help
+          Provides a hardware random number generator to the kernel.
+
+          SECURITY WARNING: It's relatively easy to eavesdrop all
+          generated random numbers from the transport stream with
+          usbmon [software] or special usb sniffer hardware.
+
+          Say N, unless your setup[i.e.: embedded system] has no
+          other rng source and you can afford to take the risk.
diff --git a/drivers/net/wireless/ath/carl9170/carl9170.h b/drivers/net/wireless/ath/carl9170/carl9170.h
index 74350d63f68..6cfbb419e2f 100644
--- a/drivers/net/wireless/ath/carl9170/carl9170.h
+++ b/drivers/net/wireless/ath/carl9170/carl9170.h
@@ -43,6 +43,7 @@
 #include <linux/firmware.h>
 #include <linux/completion.h>
 #include <linux/spinlock.h>
+#include <linux/hw_random.h>
 #include <net/cfg80211.h>
 #include <net/mac80211.h>
 #include <linux/usb.h>
@@ -449,6 +450,17 @@ struct ar9170 {
                 unsigned int off_override;
                 bool state;
         } ps;
+
+#ifdef CONFIG_CARL9170_HWRNG
+# define CARL9170_HWRNG_CACHE_SIZE      CARL9170_MAX_CMD_PAYLOAD_LEN
+        struct {
+                struct hwrng rng;
+                bool initialized;
+                char name[30 + 1];
+                u16 cache[CARL9170_HWRNG_CACHE_SIZE / sizeof(u16)];
+                unsigned int cache_idx;
+        } rng;
+#endif /* CONFIG_CARL9170_HWRNG */
 };
 
 enum carl9170_ps_off_override_reasons {
diff --git a/drivers/net/wireless/ath/carl9170/main.c b/drivers/net/wireless/ath/carl9170/main.c
index 85cb1bdebaa..782b8f3ae58 100644
--- a/drivers/net/wireless/ath/carl9170/main.c
+++ b/drivers/net/wireless/ath/carl9170/main.c
@@ -1468,6 +1468,109 @@ static int carl9170_register_wps_button(struct ar9170 *ar)
 }
 #endif /* CONFIG_CARL9170_WPC */
 
+#ifdef CONFIG_CARL9170_HWRNG
+static int carl9170_rng_get(struct ar9170 *ar)
+{
+
+#define RW      (CARL9170_MAX_CMD_PAYLOAD_LEN / sizeof(u32))
+#define RB      (CARL9170_MAX_CMD_PAYLOAD_LEN)
+
+        static const __le32 rng_load[RW] = {
+                [0 ... (RW - 1)] = cpu_to_le32(AR9170_RAND_REG_NUM)};
+
+        u32 buf[RW];
+
+        unsigned int i, off = 0, transfer, count;
+        int err;
+
+        BUILD_BUG_ON(RB > CARL9170_MAX_CMD_PAYLOAD_LEN);
+
+        if (!IS_ACCEPTING_CMD(ar) || !ar->rng.initialized)
+                return -EAGAIN;
+
+        count = ARRAY_SIZE(ar->rng.cache);
+        while (count) {
+                err = carl9170_exec_cmd(ar, CARL9170_CMD_RREG,
+                                        RB, (u8 *) rng_load,
+                                        RB, (u8 *) buf);
+                if (err)
+                        return err;
+
+                transfer = min_t(unsigned int, count, RW);
+                for (i = 0; i < transfer; i++)
+                        ar->rng.cache[off + i] = buf[i];
+
+                off += transfer;
+                count -= transfer;
+        }
+
+        ar->rng.cache_idx = 0;
+
+#undef RW
+#undef RB
+        return 0;
+}
+
+static int carl9170_rng_read(struct hwrng *rng, u32 *data)
+{
+        struct ar9170 *ar = (struct ar9170 *)rng->priv;
+        int ret = -EIO;
+
+        mutex_lock(&ar->mutex);
+        if (ar->rng.cache_idx >= ARRAY_SIZE(ar->rng.cache)) {
+                ret = carl9170_rng_get(ar);
+                if (ret) {
+                        mutex_unlock(&ar->mutex);
+                        return ret;
+                }
+        }
+
+        *data = ar->rng.cache[ar->rng.cache_idx++];
+        mutex_unlock(&ar->mutex);
+
+        return sizeof(u16);
+}
+
+static void carl9170_unregister_hwrng(struct ar9170 *ar)
+{
+        if (ar->rng.initialized) {
+                hwrng_unregister(&ar->rng.rng);
+                ar->rng.initialized = false;
+        }
+}
+
+static int carl9170_register_hwrng(struct ar9170 *ar)
+{
+        int err;
+
+        snprintf(ar->rng.name, ARRAY_SIZE(ar->rng.name),
+                 "%s_%s", KBUILD_MODNAME, wiphy_name(ar->hw->wiphy));
+        ar->rng.rng.name = ar->rng.name;
+        ar->rng.rng.data_read = carl9170_rng_read;
+        ar->rng.rng.priv = (unsigned long)ar;
+
+        if (WARN_ON(ar->rng.initialized))
+                return -EALREADY;
+
+        err = hwrng_register(&ar->rng.rng);
+        if (err) {
+                dev_err(&ar->udev->dev, "Failed to register the random "
+                        "number generator (%d)\n", err);
+                return err;
+        }
+
+        ar->rng.initialized = true;
+
+        err = carl9170_rng_get(ar);
+        if (err) {
+                carl9170_unregister_hwrng(ar);
+                return err;
+        }
+
+        return 0;
+}
+#endif /* CONFIG_CARL9170_HWRNG */
+
 static int carl9170_op_get_survey(struct ieee80211_hw *hw, int idx,
                                 struct survey_info *survey)
 {
@@ -1878,6 +1981,12 @@ int carl9170_register(struct ar9170 *ar)
                 goto err_unreg;
 #endif /* CONFIG_CARL9170_WPC */
 
+#ifdef CONFIG_CARL9170_HWRNG
+        err = carl9170_register_hwrng(ar);
+        if (err)
+                goto err_unreg;
+#endif /* CONFIG_CARL9170_HWRNG */
+
         dev_info(&ar->udev->dev, "Atheros AR9170 is registered as '%s'\n",
                  wiphy_name(ar->hw->wiphy));
 
@@ -1910,6 +2019,10 @@ void carl9170_unregister(struct ar9170 *ar)
         }
 #endif /* CONFIG_CARL9170_WPC */
 
+#ifdef CONFIG_CARL9170_HWRNG
+        carl9170_unregister_hwrng(ar);
+#endif /* CONFIG_CARL9170_HWRNG */
+
         carl9170_cancel_worker(ar);
         cancel_work_sync(&ar->restart_work);