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Commit b2bd2370 authored by Ard Biesheuvel's avatar Ard Biesheuvel Committed by Alexandre Belloni
Browse files

rtc: efi: use correct EFI 'epoch' 



The rtc-efi driver declares that the EFI 'epoch' is 1/1/1998, but
the UEFI spec does not define it at all. It does define a range of
[1900, 9999] for the 'Year' member of the EFI_TIME struct, so let's
use 1900 as the minimum year and not 1998.
Also, move the validation of the year to the convert_from_efi_time()
routine where all other EFI_TIME fields are validated as well.

This prevents rtc_read_time() failures when the RTC that backs the
EFI time services is set to a date before 1998, e.g., when it has
lost power.

This also optimizes the compute_wday() routine, by replacing the for
loop with a simple arithmetic expression, and by reusing the yearday
value that we need to compute anyway when populating the
rtc_time::tm_yday field.

Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Cc: rtc-linux@googlegroups.com
Signed-off-by: default avatarArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: default avatarAlexandre Belloni <alexandre.belloni@free-electrons.com>
parent c86a6c28

drivers/rtc/rtc-efi.c

+14 −25
Original line number Diff line number Diff line
@@ -24,10 +24,6 @@ 
#include <linux/efi.h>



#define EFI_ISDST (EFI_TIME_ADJUST_DAYLIGHT|EFI_TIME_IN_DAYLIGHT)

/*

 * EFI Epoch is 1/1/1998

 */

#define EFI_RTC_EPOCH		1998



/*

 * returns day of the year [0-365]
@@ -38,31 +34,24 @@ compute_yday(efi_time_t *eft) 
	/* efi_time_t.month is in the [1-12] so, we need -1 */

	return rtc_year_days(eft->day, eft->month - 1, eft->year);

}



/*

 * returns day of the week [0-6] 0=Sunday

 *

 * Don't try to provide a year that's before 1998, please !

 */

static int

compute_wday(efi_time_t *eft)

compute_wday(efi_time_t *eft, int yday)

{

	int y;

	int ndays = 0;



	if (eft->year < EFI_RTC_EPOCH) {

		pr_err("EFI year < " __stringify(EFI_RTC_EPOCH) ", invalid date\n");

		return -1;

	}



	for (y = EFI_RTC_EPOCH; y < eft->year; y++)

		ndays += 365 + (is_leap_year(y) ? 1 : 0);



	ndays += compute_yday(eft);

	int ndays = eft->year * (365 % 7)

		    + (eft->year - 1) / 4

		    - (eft->year - 1) / 100

		    + (eft->year - 1) / 400

		    + yday;



	/*

	 * 4=1/1/1998 was a Thursday

	 * 1/1/0000 may or may not have been a Sunday (if it ever existed at

	 * all) but assuming it was makes this calculation work correctly.

	 */

	return (ndays + 4) % 7;

	return ndays % 7;

}



static void
@@ -103,16 +92,16 @@ convert_from_efi_time(efi_time_t *eft, struct rtc_time *wtime) 
	if (!eft->month || eft->month > 12)

		return false;

	wtime->tm_mon  = eft->month - 1;

	wtime->tm_year = eft->year - 1900;



	/* day of the week [0-6], Sunday=0 */

	wtime->tm_wday = compute_wday(eft);

	if (wtime->tm_wday < 0)

	if (eft->year < 1900 || eft->year > 9999)

		return false;

	wtime->tm_year = eft->year - 1900;



	/* day in the year [1-365]*/

	wtime->tm_yday = compute_yday(eft);



	/* day of the week [0-6], Sunday=0 */

	wtime->tm_wday = compute_wday(eft, wtime->tm_yday);



	switch (eft->daylight & EFI_ISDST) {

	case EFI_ISDST: