| Message ID | 1341519557-5115-1-git-send-email-broonie@opensource.wolfsonmicro.com |
|---|---|
| State | Accepted |
| Headers | show |
On Thu, Jul 05, 2012 at 08:19:17PM -0000, Mark Brown wrote: > 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 <broonie@opensource.wolfsonmicro.com> > add_device_randomness() has only just been added in -next, this will > need to either wait until after the merge window or be merged along with > the patch adding it. Thanks, I've added this to the /dev/random git tree. - Ted
diff --git a/drivers/rtc/rtc-wm831x.c b/drivers/rtc/rtc-wm831x.c index 59c6245..ea5c6f8 100644 --- a/drivers/rtc/rtc-wm831x.c +++ b/drivers/rtc/rtc-wm831x.c @@ -24,7 +24,7 @@ #include <linux/mfd/wm831x/core.h> #include <linux/delay.h> #include <linux/platform_device.h> - +#include <linux/random.h> /* * R16416 (0x4020) - RTC Write Counter @@ -96,6 +96,26 @@ 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 */ @@ -431,6 +451,8 @@ static int wm831x_rtc_probe(struct platform_device *pdev) alm_irq, ret); } + wm831x_rtc_add_randomness(wm831x); + return 0; err:
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 <broonie@opensource.wolfsonmicro.com> --- add_device_randomness() has only just been added in -next, this will need to either wait until after the merge window or be merged along with the patch adding it. drivers/rtc/rtc-wm831x.c | 24 +++++++++++++++++++++++- 1 file changed, 23 insertions(+), 1 deletion(-)