When to burn those bridges

[John Baldwin]

On 12-Sep-2003 Doug Rabson wrote:
> On Fri, 2003-09-12 at 08:39, M. Warner Losh wrote:
>> In message: <XFMail.20030912013027.jhb at FreeBSD.org>
>>             John Baldwin <jhb at freebsd.org> writes:
>> : How do you know which drivers to detach?  Are you going to detach
>> : the generic PCI ATA driver on every kldload?  Are you going to
>> : detach the generic PCI-PCI bridge driver for PCI-PCI bridges on
>> : add-on cards for every kldload of a PCI driver?  That would be
>> : freaking insane.  The problem is that you don't know what devices
>> : a new driver might be more suitable for than existing drivers.
>> 
>> This does suck.
>> 
>> : > Besides, proble routines on self enumerating devices should look at
>> : > the IDs that anybody can look at at any time.  However, there are some
>> : > issues with some drivers that have old/new versions or that need to
>> : > ask the hardware what kind of thing it really is before making the
>> : > call.  These drivers are rare, thankfully, and even rarer are those
>> : > that have different levels.  owi/wi is the only one I know of that
>> : > fits this bill, and the only reason owi is there is to help fix wi, so
>> : > I don't think we should necessarily design to make this sort of thing
>> : > too easy....
>> : 
>> : rl(4) and re(4)?  Several drivers still allocate resources in probe(),
>> : which would break things.
>> 
>> yea, but that's a bit of a pathological case.  first, rl/re attach to
>> a specific driver, and not override.  So maybe we could mandate that
>> drivers that are generic and return negative return values should be
>> constrained to only look at the plug and play info and are not allowed
>> to look at resources.  owi/wi is the only pair that does this
>> evilness.
> 
> This is why I was thinking about a device flag which a driver would set
> if it is just a placeholder which can be pre-empted safely.

Yes, I wish we had better drivers so we didn't have to do that, but
that might be the best for now.

-- 

John Baldwin <jhb at FreeBSD.org>  <><  http://www.FreeBSD.org/~jhb/
"Power Users Use the Power to Serve!"  -  http://www.FreeBSD.org/