Re: Is it useful to support user level drivers

[Abramo Bagnara <abramo@alsa-project.org>]

Alan Cox wrote:
> 
> > (i.e. counted). An alternative to queuing (user selectable) is to block
> > interrupt generation at hardware level in kernel space immediately
> > before notification.
> >
> > I'm missing something?
> 
> IRQ 9 shared between user space app and disk. IRQ arrives is disabled and
> reported, app wakes up, app wants to page in code, IRQ is disabled, box dies
> 
> You have to handle that in kernel space, at least enough to handle the
> irq event, ack it and queue the data

I try to be more clear:

Kernel space:
- irq 9 arrives from our device
- interrupts are disabled
- our kernel space micro handler is invoked
- interrupt source is checked
- if no notification is pending a signal is notificated for user space
(or a process is marked runnable)
- optionally our device interrupt generation is disabled
- handler returns
- interrupts are enabled

User space:
- signal arrive (or process is restarted)
- action is done
- notification is acknowledged (using an ioctl)

Kernel space:
- if we have other notifications to do, do one
- optionally our device interrupt generation is reenabled

-- 
Abramo Bagnara                       mailto:abramo@alsa-project.org

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It sounds good!