[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCH 8/9] isa: refine irq reservations

From: Gerd Hoffmann
Subject: Re: [Qemu-devel] [PATCH 8/9] isa: refine irq reservations
Date: Tue, 15 Sep 2009 09:23:41 +0200
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20090814 Fedora/3.0-2.6.b3.fc11 Lightning/1.0pre Thunderbird/3.0b3

On 09/14/09 18:55, Blue Swirl wrote:
On Mon, Sep 14, 2009 at 6:49 PM, Gerd Hoffmann<address@hidden>  wrote:
There are a few cases where IRQ sharing on the ISA bus is used and
possible.  In general only devices of the same kind can do that.
A few use cases:

  * serial lines 1+3 share irq 4
  * serial lines 2+4 share irq 3
  * parallel ports share irq 7
  * ppc/prep: ide ports share irq 13

There is another ppc/prep case where RTC and m48t59 share irq 8. The
attached patch converts m48t59 to ISA and makes this more visible.

Hmm, ok. So scratch this and maybe use a 'sharing the irq is is fine with me' flag instead?

Does sharing of IRQs really have to be fatal? Wasn't ISA bus edge
triggered and so IRQ sharing was a bit unreliable (but not completely
broken) also on real HW?

Well, the fundamental problem is that (1) the drivers must be prepared to handle that and (b) the hardware must be designed sanely. There are cases where it works fine (see the list above). It isn't true in general though. You can't configure two random devices (say sb16 + ne2k) to share the same irq and expect everything to work fine.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]