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Subject[PATCH v3 03/03]: hwrng: khwrngd derating per device

This patch introduces a derating factor to struct hwrng for
the random bits going into the kernel input pool, and a common
default derating for drivers which do not specify one.

Signed-off-by: Torsten Duwe <duwe@suse.de>

---
drivers/char/hw_random/core.c | 11 ++++++++++-
include/linux/hw_random.h | 3 +++
2 files changed, 13 insertions(+), 1 deletion(-)

--- linux/include/linux/hw_random.h.orig
+++ linux/include/linux/hw_random.h
@@ -29,6 +29,8 @@
* @read: New API. drivers can fill up to max bytes of data
* into the buffer. The buffer is aligned for any type.
* @priv: Private data, for use by the RNG driver.
+ * @derating: Estimation of true entropy in RNG's bitstream
+ * (per mill).
*/
struct hwrng {
const char *name;
@@ -38,6 +39,7 @@ struct hwrng {
int (*data_read)(struct hwrng *rng, u32 *data);
int (*read)(struct hwrng *rng, void *data, size_t max, bool wait);
unsigned long priv;
+ unsigned short derating;

/* internal. */
struct list_head list;
--- linux/drivers/char/hw_random/core.c.orig
+++ linux/drivers/char/hw_random/core.c
@@ -56,11 +56,15 @@ static LIST_HEAD(rng_list);
static DEFINE_MUTEX(rng_mutex);
static int data_avail;
static u8 *rng_buffer, *rng_fillbuf;
-static unsigned short derating_current = 700; /* an arbitrary 70% */
+static unsigned short derating_current;
+static unsigned short derating_default = 500; /* an arbitrary 50% */

module_param(derating_current, ushort, 0644);
MODULE_PARM_DESC(derating_current,
"current hwrng entropy estimation per mill");
+module_param(derating_default, ushort, 0644);
+MODULE_PARM_DESC(derating_default,
+ "default entropy content of hwrng per mill");

static void start_khwrngd(void);

@@ -79,6 +83,11 @@ static inline int hwrng_init(struct hwrn
if (err)
return err;

+ derating_current = rng->derating ? : derating_default;
+ derating_current &= 1023;
+
+ if (derating_current == 0 && hwrng_fill)
+ kthread_stop(hwrng_fill);
if (derating_current > 0 && !hwrng_fill)
start_khwrngd();


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