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Date: Fri, 11 Apr 2008 15:20:14 +0200 From: Clemens Ladisch <clemens@...isch.de> To: Dimitri Gorokhovik <dimitri.gorokhovik@...com.fr> CC: tglx@...utronix.de, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [RFC][PATCH] HPET: register additional counter-only char device Dimitri Gorokhovik wrote: > I need to have many processes all reading from userspace the counter register > of the (same) HPET hardware. Just reading counter values, not handling timers, > enabling/disabling interrupts etc. `/dev/hpet' doesn't allow for this, as the > number of times it can be opened is limited by the number of timers available. Indeed. The driver assumes that userspace wants to program its own timer (like an RTC device). Allowing mmap() on the hardware counter was more an afterthought. > What would be the right way to implement such a support? For now, I simply > register a new misc device, '/dev/hpetctr', along with '/dev/hpet', for the same > ACPI device and on the same occasion. Your patch circumvents CONFIG_HPET_MMAP. Another possibility would be to allow the device to be opened infinitely many times but not to allocate a hardware timer until one of the ioctls is called. This means that opening /dev/hpet does not guarantee that a timer is available, but this has already been possible previously because request_irq() might fail. Regards, Clemens -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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