linux-kernel - Re: [rtc-linux] [PATCH 1/3] rtc: omap: Unlock and Lock rtc registers before and after register writes

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Message-ID: <20150401155204.GC20669@piout.net>
Date:	Wed, 1 Apr 2015 17:52:04 +0200
From:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
To:	rtc-linux@...glegroups.com
Cc:	a.zummo@...ertech.it, t-kristo@...com, nsekhar@...com,
	linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org,
	lokeshvutla@...com
Subject: Re: [rtc-linux] [PATCH 1/3] rtc: omap: Unlock and Lock rtc registers
 before and after register writes

Hi,

On 01/04/2015 at 11:24:56 +0530, Lokesh Vutla wrote :
> RTC module contains a kicker mechanism to prevent any spurious writes
> from changing the register values. This mechanism requires two MMR
> writes to the KICK0 and KICK1 registers with exact data values
> before the kicker lock mechanism is released.
> 
> Currently the driver release the lock in the probe and leaves it enabled
> until the rtc driver removal. This eliminates the idea of preventing
> spurious writes when RTC driver is loaded.
> So implement rtc lock and unlock functions before and after register writes.
> 
> Signed-off-by: Lokesh Vutla <lokeshvutla@...com>
> ---
> - This is as advised by Paul to implement lock and unlock functions in
>   the driver and not to unlock and leave it in probe.
>   The same discussion can be seen here:
>   http://www.mail-archive.com/linux-omap%40vger.kernel.org/msg111588.html
> 
>  drivers/rtc/rtc-omap.c | 46 ++++++++++++++++++++++++++++++++++++++--------
>  1 file changed, 38 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-omap.c b/drivers/rtc/rtc-omap.c
> index 8e5851a..96cc613 100644
> --- a/drivers/rtc/rtc-omap.c
> +++ b/drivers/rtc/rtc-omap.c
> @@ -156,6 +156,22 @@ static inline void rtc_writel(struct omap_rtc *rtc, unsigned int reg, u32 val)
>  	writel(val, rtc->base + reg);
>  }
>  
> +static void rtc_unlock(struct omap_rtc *rtc)
> +{
> +	if (rtc->type->has_kicker) {

Instead of testing for has_kicker each time, I would add .lock and
.unlock to omap_rtc_device_type and directly use rtc->type->lock and
rtc->type->unlock.

> +		rtc_writel(rtc, OMAP_RTC_KICK0_REG, KICK0_VALUE);
> +		rtc_writel(rtc, OMAP_RTC_KICK1_REG, KICK1_VALUE);
> +	}
> +}
> +
-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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