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UPSTREAM: rtc: Check update-in-progress bit

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While the real-time clock updates its count, values may not be correctly
read or written.  On reads, ensure the UIP bit is clear which guarantees
a minimum of 244 microseconds exists before the update begins.  Writes
already avoid the problem by disabling the RTC count via the SET bit.

BUG=None
BRANCH=None
TEST=None

Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Reviewed-on: https://review.coreboot.org/17369
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

Change-Id: I39e34493113015d32582f1c280fafa9e97f43a40
Reviewed-on: https://chromium-review.googlesource.com/412852
Commit-Ready: Furquan Shaikh <furquan@chromium.org>
Tested-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
This commit is contained in:
Marshall Dawson 2016-11-05 18:31:33 -06:00 • committed by chrome-bot
commit ae1dc9a24d
2 changed files with 12 additions and 0 deletions
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10
src/include/pc80/mc146818rtc.h
View file

@ -112,6 +112,16 @@ static inline unsigned char cmos_read(unsigned char addr)
return inb(RTC_BASE_PORT + offs + 1);
}
/* Upon return the caller is guaranteed 244 microseconds to complete any
* RTC operations. wait_uip may be called a single time prior to multiple
* accesses, but sequences requiring more time should call wait_uip again.
*/
static inline void wait_uip(void)
{
while (cmos_read(RTC_REG_A) & RTC_UIP)
;
}
static inline void cmos_write_inner(unsigned char val, unsigned char addr)
{
int offs = 0;