]> git.proxmox.com Git - mirror_ubuntu-eoan-kernel.git/commit
drivers/rtc/rtc-rk808.c: fix rtc time reading issue
authorChris Zhong <zyw@rock-chips.com>
Fri, 13 Feb 2015 22:40:54 +0000 (14:40 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Sat, 14 Feb 2015 05:21:43 +0000 (21:21 -0800)
commitc412c6034aaf38ff718296f3b77cb8e76b541985
tree8714c27538a638e3a927609b9a6d4bf195aa7cef
parent1ef2816f26a1d962d6317f7545218fa2ae3643bb
drivers/rtc/rtc-rk808.c: fix rtc time reading issue

After we set the GET_TIME bit, the rtc time can't be read immediately.  We
should wait up to 31.25 us, about one cycle of 32khz.  Otherwise reading
RTC time will return a old time.  If we clear the GET_TIME bit after
setting, the time of i2c transfer is certainly more than 31.25us.

Doug said:

: I think we are safe.  At 400kHz (the max speed of this part) each bit can
: be transferred no faster than 2.5us.  In order to do a valid i2c
: transaction we need to _at least_ write the address of the device and the
: data onto the bus, which is 16 bits.  16 * 2.5us = 40us.  That's above the
: 31.25us

[akpm@linux-foundation.org: tweak comment per review discussion]
Signed-off-by: Chris Zhong <zyw@rock-chips.com>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Cc: Sonny Rao <sonnyrao@chromium.org>
Cc: Heiko Stübner <heiko@sntech.de>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
drivers/rtc/rtc-rk808.c