linux-kernel - Re: [PATCH] rtc-ds1302: handle write protection

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Date:	Thu, 30 May 2013 12:20:33 +0200
From:	Marc Zyngier <maz@...terjones.org>
To:	Sergey Yanovich <ynvich@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	<rtc-linux@...glegroups.com>, <linux-kernel@...r.kernel.org>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Sachin Kamat <sachin.kamat@...aro.org>,
	Jingoo Han <jg1.han@...sung.com>
Subject: Re: [PATCH] rtc-ds1302: handle write protection

On Thu, 30 May 2013 14:14:42 +0400, Sergey Yanovich <ynvich@...il.com>
wrote:
> On Wed, 2013-05-29 at 15:53 -0700, Andrew Morton wrote:
>> On Tue, 21 May 2013 03:21:30 +0400 Sergey Yanovich <ynvich@...il.com>
>> wrote:
>> @@ -321,6 +326,7 @@ static int ds1302_rtc_remove(struct platform_device
>> *pdev)
>> >  {
>> >  	struct rtc_device *rtc = platform_get_drvdata(pdev);
>> >  
>> > +	ds1302_writebyte(RTC_ADDR_CTRL, RTC_CMD_WRITE_DISABLE);
>> >  	rtc_device_unregister(rtc);
>> >  	platform_set_drvdata(pdev, NULL);
>> 
>> ds1302_rtc_remove() no longer exists in my tree - it got whittled away
>> to nothing by
>>
http://ozlabs.org/~akpm/mmots/broken-out/rtc-rtc-ds1302-remove-unnecessary-platform_set_drvdata.patch
>> and
>>
http://ozlabs.org/~akpm/mmots/broken-out/drivers-rtc-rtc-ds1302c-remove-empty-function.patch
>> 
>> Perhaps it should be re-added for this?
> 
> There are 2 options. I would be happy with either.
> 
> 1. I've chosen 'probe/remove' to enable/disable write access.
> 
> 2. Another option is to wrap enable/disable around
> ds1302_rtc_set_time().
> 
> IIUC, the former saves a few bytes of memory. However, now, when
> ds1302_rtc_remove() is gone, the latter looks better. So I could rewrite
> the patch either way.

Option two looks actually safer to me, as it ensures that an unexpected
reboot outside of the set_time section doesn't leave write access enabled.
You never know what firmware could do while you're not looking...

         M.
-- 
Who you jivin' with that Cosmik Debris?
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