From 66e540e96c3ad9e73e49e0fc7292bfe5d5e2bb11 Mon Sep 17 00:00:00 2001 From: Mark Brown Date: Thu, 5 Jul 2012 20:19:17 +0000 Subject: rtc: wm831x: Feed the write counter into device_add_randomness() commit 9dccf55f4cb011a7552a8a2749a580662f5ed8ed upstream. The tamper evident features of the RTC include the "write counter" which is a pseudo-random number regenerated whenever we set the RTC. Since this value is unpredictable it should provide some useful seeding to the random number generator. Only do this on boot since the goal is to seed the pool rather than add useful entropy. Signed-off-by: Mark Brown Signed-off-by: Theodore Ts'o Signed-off-by: Paul Gortmaker Signed-off-by: Willy Tarreau --- drivers/rtc/rtc-wm831x.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-) diff --git a/drivers/rtc/rtc-wm831x.c b/drivers/rtc/rtc-wm831x.c index 79795cdf6ed8..daefe66f3501 100644 --- a/drivers/rtc/rtc-wm831x.c +++ b/drivers/rtc/rtc-wm831x.c @@ -23,7 +23,7 @@ #include #include #include - +#include /* * R16416 (0x4020) - RTC Write Counter @@ -95,6 +95,26 @@ struct wm831x_rtc { unsigned int alarm_enabled:1; }; +static void wm831x_rtc_add_randomness(struct wm831x *wm831x) +{ + int ret; + u16 reg; + + /* + * The write counter contains a pseudo-random number which is + * regenerated every time we set the RTC so it should be a + * useful per-system source of entropy. + */ + ret = wm831x_reg_read(wm831x, WM831X_RTC_WRITE_COUNTER); + if (ret >= 0) { + reg = ret; + add_device_randomness(®, sizeof(reg)); + } else { + dev_warn(wm831x->dev, "Failed to read RTC write counter: %d\n", + ret); + } +} + /* * Read current time and date in RTC */ @@ -464,6 +484,8 @@ static int wm831x_rtc_probe(struct platform_device *pdev) alm_irq, ret); } + wm831x_rtc_add_randomness(wm831x); + return 0; err: -- cgit v1.2.3