Linux-RTC Archive on lore.kernel.org
 help / Atom feed
* [PATCH] rtc: cmos: ignore bogus century byte
@ 2019-01-06  8:21 Eric Wong
  2019-01-10 21:33 ` Alexandre Belloni
  0 siblings, 1 reply; 3+ messages in thread
From: Eric Wong @ 2019-01-06  8:21 UTC (permalink / raw)
  To: Alexandre Belloni, Alessandro Zummo
  Cc: Sylvain Chouleur, Patrick McDermott, linux-rtc, linux-kernel

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 <alexandre.belloni@bootlin.com>
Cc: Alessandro Zummo <a.zummo@towertech.it>
Cc: Sylvain Chouleur <sylvain.chouleur@intel.com>
Cc: Patrick McDermott <patrick.mcdermott@libiquity.com>
Cc: linux-rtc@vger.kernel.org
Signed-off-by: Eric Wong <e@80x24.org>
---
 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

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] rtc: cmos: ignore bogus century byte
  2019-01-06  8:21 [PATCH] rtc: cmos: ignore bogus century byte Eric Wong
@ 2019-01-10 21:33 ` Alexandre Belloni
  2019-01-10 21:56   ` Eric Wong
  0 siblings, 1 reply; 3+ messages in thread
From: Alexandre Belloni @ 2019-01-10 21:33 UTC (permalink / raw)
  To: Eric Wong
  Cc: Alessandro Zummo, Sylvain Chouleur, Patrick McDermott, linux-rtc,
	linux-kernel

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 <alexandre.belloni@bootlin.com>
> Cc: Alessandro Zummo <a.zummo@towertech.it>
> Cc: Sylvain Chouleur <sylvain.chouleur@intel.com>
> Cc: Patrick McDermott <patrick.mcdermott@libiquity.com>
> Cc: linux-rtc@vger.kernel.org
> Signed-off-by: Eric Wong <e@80x24.org>
> ---
>  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

^ permalink raw reply	[flat|nested] 3+ messages in thread

* Re: [PATCH] rtc: cmos: ignore bogus century byte
  2019-01-10 21:33 ` Alexandre Belloni
@ 2019-01-10 21:56   ` Eric Wong
  0 siblings, 0 replies; 3+ messages in thread
From: Eric Wong @ 2019-01-10 21:56 UTC (permalink / raw)
  To: Alexandre Belloni, Patrick McDermott
  Cc: Alessandro Zummo, Sylvain Chouleur, linux-rtc, linux-kernel

Alexandre Belloni <alexandre.belloni@bootlin.com> 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.

^ permalink raw reply	[flat|nested] 3+ messages in thread

end of thread, back to index

Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-01-06  8:21 [PATCH] rtc: cmos: ignore bogus century byte Eric Wong
2019-01-10 21:33 ` Alexandre Belloni
2019-01-10 21:56   ` Eric Wong

Linux-RTC Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-rtc/0 linux-rtc/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-rtc linux-rtc/ https://lore.kernel.org/linux-rtc \
		linux-rtc@vger.kernel.org linux-rtc@archiver.kernel.org
	public-inbox-index linux-rtc


Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-rtc


AGPL code for this site: git clone https://public-inbox.org/ public-inbox