linux-kernel - Re: [PATCH 6/7] ARM: rtc: update CMOS RTC to support MMIO and private lock

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Message-ID: <535A55F7.8030506@arm.com>
Date:	Fri, 25 Apr 2014 13:32:55 +0100
From:	Marc Zyngier <marc.zyngier@....com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"rtc-linux@...glegroups.com" <rtc-linux@...glegroups.com>,
	Will Deacon <Will.Deacon@....com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Alessandro Zummo <a.zummo@...ertech.it>
Subject: Re: [PATCH 6/7] ARM: rtc: update CMOS RTC to support MMIO and private
 lock

Hi Russell,

On 25/04/14 11:27, Russell King - ARM Linux wrote:
> On Fri, Apr 25, 2014 at 10:31:14AM +0100, Marc Zyngier wrote:
>> So far, the CMOS RTC (PC-style mc146818) has always been used
>> through an ISA I/O port of some sort, with each platform configuring
>> the address in a static way.
>>
>> Some platforms (KVM with kvmtools, for example) offer a MMIO version
>> of the CMOS RTC, which requires a different access method.
>>
>> This patch select the RTC_DRV_CMOS_MMIO configuration in order to
>> support MMIO accesses as well as the older IO port method.
>>
>> While we're at it, switch to RTC_DRV_CMOS_PRIV_LOCK and remove the
>> ancient rtc_lock.
> 
> rtc_lock is there so that if you build the RTC driver and nvram driver
> in, and load them, they will both want to access the RTC via its
> indexed registers, and they need to share the lock to avoid trampling
> on each others toes.

Ah, I completely missed that one. Note to self: never look at that kind
of code just after lunch...

> Yes, it should be handled in a more modern way, but I don't think you
> can simply get rid of this in this manner.  We can have both these
> drivers loaded on ARM platforms.

Agreed. I suppose that would have to be handled by some kind of module
dependency, but it is starting to look even uglier than I initially thought.

Back to the drawing board...

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...
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