linux-kernel - Re: [PATCH] RTC: Add mmap method to rtc character driver

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Message-ID: <44C6B925.8040606@zytor.com>
Date:	Tue, 25 Jul 2006 17:36:53 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Neil Horman <nhorman@...driver.com>
CC:	Segher Boessenkool <segher@...nel.crashing.org>,
	Dave Airlie <airlied@...il.com>, linux-kernel@...r.kernel.org,
	a.zummo@...ertech.it, jg@...edesktop.org
Subject: Re: [PATCH] RTC: Add mmap method to rtc character driver

Neil Horman wrote:
>>>>
>>> It there any arch for which the rtc driver doesn't function?
>> Yes, there are plenty of systems which don't have an RTC, or have an RTC 
>> which can't generate interrupts.
>>
> Ok, for those implementations which don't have an RTC that the rtc driver can
> drive, the mmap functionality will not work, but at that point what interface
> are you left with at all for obtaining periodic time?

Depends completely on the hardware.  Some hardware will rely on cycle 
counters, some may rely on I/O devices which may or may not be mappable 
into user space, and some will have to enter the kernel.

These aren't compatible with your programming model.

	-hpa
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