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Kernel: Ensure we read valid values from the RTC CMOS registers

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We try to read twice from the RTC CMOS registers, and if the values are
not the same for 5 attempts, we know there's a malfunction with the
hardware so we declare these values as bogus in the kernel log.
This commit is contained in:
Liav A 2021-07-27 20:26:22 +03:00 committed by Andreas Kling
parent 517460d3a9
commit 7c617394a1
Notes: sideshowbarker 2024-07-18 07:29:18 +09:00 
Author: https://github.com/supercomputer7
Commit: https://github.com/SerenityOS/serenity/commit/7c617394a15
Pull-request: https://github.com/SerenityOS/serenity/pull/8964
Reviewed-by: https://github.com/awesomekling
Reviewed-by: https://github.com/caoimhebyrne
2 changed files with 20 additions and 10 deletions
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29
Kernel/RTC.cpp
View File

@ -33,7 +33,7 @@ static u8 bcd_to_binary(u8 bcd)
return (bcd & 0x0F) + ((bcd >> 4) * 10);
}
void read_registers(unsigned& year, unsigned& month, unsigned& day, unsigned& hour, unsigned& minute, unsigned& second)
static bool try_to_read_registers(unsigned& year, unsigned& month, unsigned& day, unsigned& hour, unsigned& minute, unsigned& second)
{
// Note: Let's wait 0.01 seconds until we stop trying to query the RTC CMOS
size_t time_passed_in_milliseconds = 0;
@ -54,7 +54,7 @@ void read_registers(unsigned& year, unsigned& month, unsigned& day, unsigned& ho
hour = 0;
minute = 0;
second = 0;
return;
return false;
}
u8 status_b = CMOS::read(0x0b);
@ -85,20 +85,31 @@ void read_registers(unsigned& year, unsigned& month, unsigned& day, unsigned& ho
}
year += 2000;
return true;
}
time_t now()
{
// FIXME: We should probably do something more robust here.
// Perhaps read all the values twice and verify that they were identical.
// We don't want to be caught in the middle of an RTC register update.
while (update_in_progress())
;
auto check_registers_against_preloaded_values = [](unsigned year, unsigned month, unsigned day, unsigned hour, unsigned minute, unsigned second) {
unsigned checked_year, checked_month, checked_day, checked_hour, checked_minute, checked_second;
if (!try_to_read_registers(checked_year, checked_month, checked_day, checked_hour, checked_minute, checked_second))
return false;
return checked_year == year && checked_month == month && checked_day == day && checked_hour == hour && checked_minute == minute && checked_second == second;
};
unsigned year, month, day, hour, minute, second;
read_registers(year, month, day, hour, minute, second);
bool did_read_rtc_sucessfully = false;
for (size_t attempt = 0; attempt < 5; attempt++) {
if (!try_to_read_registers(year, month, day, hour, minute, second))
break;
if (check_registers_against_preloaded_values(year, month, day, hour, minute, second)) {
did_read_rtc_sucessfully = true;
break;
}
}
dmesgln("RTC: Year: {}, month: {}, day: {}, hour: {}, minute: {}, second: {}", year, month, day, hour, minute, second);
dmesgln("RTC: {} Year: {}, month: {}, day: {}, hour: {}, minute: {}, second: {}", (did_read_rtc_sucessfully ? "" : "(failed to read)"), year, month, day, hour, minute, second);
time_t days_since_epoch = years_to_days_since_epoch(year) + day_of_year(year, month, day);
return ((days_since_epoch * 24 + hour) * 60 + minute) * 60 + second;

1
Kernel/RTC.h
View File

@ -13,6 +13,5 @@ namespace RTC {
void initialize();
time_t now();
time_t boot_time();
void read_registers(unsigned& year, unsigned& month, unsigned& day, unsigned& hour, unsigned& minute, unsigned& second);
}