Date: Thu, 22 Feb 1996 21:23:25 +1100 From: Bruce Evans <bde@zeta.org.au> To: koshy@india.hp.com, seki@sysrap.cs.fujitsu.co.jp Cc: hackers@FreeBSD.org, smpatel@wam.umd.edu Subject: Re: ISA device irq/mem auto-configuration Message-ID: <199602221023.VAA04262@godzilla.zeta.org.au>
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>A question here: if a card is determined (by reading the hardware) to >reside at port 0x300 and IRQ 5, can we change the kernel isa_dev structure >overwriting the configured values in the structure? >The question is: Is this a safe thing to do in general? It's safe if a successful probe doesn't leave the device active or the device driver with state that depends on the device being attached. The SCSI drivers have always overwritten the configured values (including the non-auto values :-(). The conflict check in isa.c is repeated after successful probes in case anything has changed. If there is a conflict (with a previously attached device) then the device won't be attached, so the driver must not leave anything active. >My thinking was that reconfiguring the hardware shouldn't be part of >the regular driver. For one it violates the principle of least surprise; >for example if a user is running DOS and FreeBSD. We would want the BSD >driver to change settings on the card every time it boots forcing the user >to re-run his DOS config utilities everytime. >Secondly, configuring software configurable cards adds another >magnitude of complexity and board model dependence to the driver. I agree. >Thirdly, FreeBSD's pre-configured idea of interrupts and IO addresses may clash >with some other hardware present on the system. The preconfigured settings should be "auto" if possible, but this would require complications to determine settings that don't conflict with other devices. The complications would usually be a waste of time - except when a new card is added, the current settings shouldn't conflict and the drivers shouldn't change them. Bruce
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