linux-kernel - Re: [PATCH V2] rtc: mc146818: Dont test for bit 0-5 in Register D

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Message-ID: <2b5d8143-f49d-409b-49f1-556366b9d70c@digikod.net>
Date:   Wed, 3 Feb 2021 14:00:13 +0100
From:   Mickaël Salaün <mic@...ikod.net>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Serge Belyshev <belyshev@...ni.sinp.msu.ru>
Cc:     Dirk Gouders <dirk@...ders.net>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Miroslav Lichvar <mlichvar@...hat.com>,
        John Stultz <john.stultz@...aro.org>,
        Prarit Bhargava <prarit@...hat.com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        linux-rtc@...r.kernel.org, Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH V2] rtc: mc146818: Dont test for bit 0-5 in Register D

FWIW, it's still OK for me.

Tested-by: Mickaël Salaün <mic@...ux.microsoft.com>

On 01/02/2021 20:24, Thomas Gleixner wrote:
> The recent change to validate the RTC turned out to be overly tight.
> 
> While it cures the problem on the reporters machine it breaks machines
> with Intel chipsets which use bit 0-5 of the D register. So check only
> for bit 6 being 0 which is the case on these Intel machines as well.
> 
> Fixes: 211e5db19d15 ("rtc: mc146818: Detect and handle broken RTCs")
> Reported-by: Serge Belyshev <belyshev@...ni.sinp.msu.ru>
> Reported-by: Dirk Gouders <dirk@...ders.net>
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
> V2: Provide the actual delta patch. Should have stayed away from
>     computers today....
> ---
>  drivers/rtc/rtc-cmos.c         |    4 ++--
>  drivers/rtc/rtc-mc146818-lib.c |    4 ++--
>  2 files changed, 4 insertions(+), 4 deletions(-)
> 
> --- a/drivers/rtc/rtc-cmos.c
> +++ b/drivers/rtc/rtc-cmos.c
> @@ -805,8 +805,8 @@ cmos_do_probe(struct device *dev, struct
>  
>  	spin_lock_irq(&rtc_lock);
>  
> -	/* Ensure that the RTC is accessible. Bit 0-6 must be 0! */
> -	if ((CMOS_READ(RTC_VALID) & 0x7f) != 0) {
> +	/* Ensure that the RTC is accessible. Bit 6 must be 0! */
> +	if ((CMOS_READ(RTC_VALID) & 0x40) != 0) {
>  		spin_unlock_irq(&rtc_lock);
>  		dev_warn(dev, "not accessible\n");
>  		retval = -ENXIO;
> --- a/drivers/rtc/rtc-mc146818-lib.c
> +++ b/drivers/rtc/rtc-mc146818-lib.c
> @@ -21,8 +21,8 @@ unsigned int mc146818_get_time(struct rt
>  
>  again:
>  	spin_lock_irqsave(&rtc_lock, flags);
> -	/* Ensure that the RTC is accessible. Bit 0-6 must be 0! */
> -	if (WARN_ON_ONCE((CMOS_READ(RTC_VALID) & 0x7f) != 0)) {
> +	/* Ensure that the RTC is accessible. Bit 6 must be 0! */
> +	if (WARN_ON_ONCE((CMOS_READ(RTC_VALID) & 0x40) != 0)) {
>  		spin_unlock_irqrestore(&rtc_lock, flags);
>  		memset(time, 0xff, sizeof(*time));
>  		return 0;
>