linux-kernel - Re: HPET mmap() problem

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Date:	Mon, 16 Mar 2009 11:01:09 +0100
From:	Clemens Ladisch <clemens@...isch.de>
To:	Jussi Laako <jussi@...arnerd.net>
CC:	linux-kernel@...r.kernel.org
Subject: Re: HPET mmap() problem

Jussi Laako wrote:
> In the JACK audio connection kit we have support for mmap() of /dev/hpet
> as our time source (as one of the possibilities). However, there's a
> nasty issue with the current driver as it reserves one of the three
> comparator-timers per each open() and denies further opens when the
> timers are exhausted. And in case it's already used as a system clock
> source, two of the timers are already reserved...
> 
> However, we are only interested on the main counter value, and would
> like to have unlimited access from number of processes to this value
> through mmap() of the device.
> 
> Any ideas/recommendations/suggestions on which way to change the driver
> to support this?

Don't allocate a hpet_dev in hpet_open but when hpet_ioctl is called for
the first time.

> Or even better, if someone is already working on this?

I'm planning to work on this.


HTH
Clemens
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