LinuxLists.cc - [PATCH] rtc: cmos: ignore bogus century byte

2019-01-06 08:25:09

Subject: [PATCH] rtc: cmos: ignore bogus century byte

Older versions of Libreboot and Coreboot had an invalid value
(`3' in my case) in the century byte affecting the GM45 in
the Thinkpad X200. Not everybody's updated their firmwares,
and Linux <= 4.2 was able to read the RTC without problems,
so workaround this by ignoring invalid values.

Fixes: 3c217e51d8a272b9 ("rtc: cmos: century support")

Cc: Alexandre Belloni <[email protected]>
Cc: Alessandro Zummo <[email protected]>
Cc: Sylvain Chouleur <[email protected]>
Cc: Patrick McDermott <[email protected]>
Cc: [email protected]
Signed-off-by: Eric Wong <[email protected]>
---
drivers/rtc/rtc-mc146818-lib.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
index 2f1772a358ca..18a6f15e313d 100644
--- a/drivers/rtc/rtc-mc146818-lib.c
+++ b/drivers/rtc/rtc-mc146818-lib.c
@@ -82,7 +82,7 @@ unsigned int mc146818_get_time(struct rtc_time *time)
time->tm_year += real_year - 72;
#endif

- if (century)
+ if (century > 20)
time->tm_year += (century - 19) * 100;

/*
--
EW

2019-01-10 22:04:10

by Alexandre Belloni

[permalink] [raw]

Subject: Re: [PATCH] rtc: cmos: ignore bogus century byte

On 06/01/2019 08:21:03+0000, Eric Wong wrote:
> Older versions of Libreboot and Coreboot had an invalid value
> (`3' in my case) in the century byte affecting the GM45 in
> the Thinkpad X200. Not everybody's updated their firmwares,
> and Linux <= 4.2 was able to read the RTC without problems,
> so workaround this by ignoring invalid values.
>

Does this mean that it is set to an invalid value and that in is not
getting updated properly in mc146818_set_time?

> Fixes: 3c217e51d8a272b9 ("rtc: cmos: century support")
>
> Cc: Alexandre Belloni <[email protected]>
> Cc: Alessandro Zummo <[email protected]>
> Cc: Sylvain Chouleur <[email protected]>
> Cc: Patrick McDermott <[email protected]>
> Cc: [email protected]
> Signed-off-by: Eric Wong <[email protected]>
> ---
> drivers/rtc/rtc-mc146818-lib.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/rtc/rtc-mc146818-lib.c b/drivers/rtc/rtc-mc146818-lib.c
> index 2f1772a358ca..18a6f15e313d 100644
> --- a/drivers/rtc/rtc-mc146818-lib.c
> +++ b/drivers/rtc/rtc-mc146818-lib.c
> @@ -82,7 +82,7 @@ unsigned int mc146818_get_time(struct rtc_time *time)
> time->tm_year += real_year - 72;
> #endif
>
> - if (century)
> + if (century > 20)
> time->tm_year += (century - 19) * 100;
>
> /*
> --
> EW

--
Alexandre Belloni, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

2019-01-10 22:10:00

by Eric Wong

[permalink] [raw]

Subject: Re: [PATCH] rtc: cmos: ignore bogus century byte

Alexandre Belloni <[email protected]> wrote:
> Does this mean that it is set to an invalid value and that in is not
> getting updated properly in mc146818_set_time?

It seems to be set/updated without trouble while the machine is
on. It's only on a cold boot (from poweroff or hibernate) that
the value is invalid.

Patrick may be able to fill you in on more details.

2019-01-22 18:08:04

by Alexandre Belloni

[permalink] [raw]