From owner-freebsd-alpha  Fri Nov 17 14:18:42 2000
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From: =?ISO-8859-1?Q?G=E9rard_Roudier?= <groudier@club-internet.fr>
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To: Andrew Gallatin <gallatin@cs.duke.edu>
Cc: Bernd Walter <ticso@cicely8.cicely.de>,
	John Baldwin <jhb@FreeBSD.ORG>,
	Christian Weisgerber <naddy@mips.inka.de>, freebsd-alpha@FreeBSD.ORG
Subject: Re: PC164 IDE only works (was: SMPng stability)
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On Fri, 17 Nov 2000, Andrew Gallatin wrote:

>=20
> An interesting comment found in the linux kernel sources:
>=20
>         /* In theory, the PC164 has the same interrupt hardware as
>            the other Cabriolet based systems.  However, something=20
>            got screwed up late in the development cycle which broke
>            the interrupt masking hardware.  Repeat, it is not=20
>            possible to mask and ack interrupts.  At all.
>=20
>            In an attempt to work around this, while processing=20
>            interrupts, we do not allow the IPL to drop below what
>            it is currently.  This prevents the possibility of
>            recursion. =20
>=20
>            ??? Another option might be to force all PCI devices
>            to use edge triggered rather than level triggered
>            interrupts.  That might be too invasive though.  */
>=20
>=20
> Drew

Interesting, indeed.

Note that using edge triggerred interrupt for PCI devices is a broken
idea, since it would just break numerous drivers by making them lose
interrupt conditions. Btw, in my opinion, handling level sensitive
interrupts from some scheduled entity (i.e. not in the corresponding
interrupt context) does not look a better idea to me for other reasons.
This let me consider the above hardware not to be broken given proper
handling of level sensitive interrupts.

  G=E9rard.



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