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From: Scott Long <scottl@samsco.org>
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To: Andriy Gapon <avg@freebsd.org>
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Cc: arch@freebsd.org, Rick Macklem <rmacklem@uoguelph.ca>
Subject: Re: (in)appropriate uses for MAXBSIZE
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On Apr 9, 2010, at 8:41 AM, Andriy Gapon wrote:
> on 09/04/2010 17:35 Scott Long said the following:
>> On Apr 9, 2010, at 8:29 AM, Andriy Gapon wrote:
>>=20
>>> on 09/04/2010 16:52 Scott Long said the following:
>>>> Storage drivers are insulated from the details of MAXBSIZE by GEOM =
honoring
>>>> the driver's advertised max-i/o-size attribute.  What I see when I =
grep through the
>>>> sources are mostly uses in busdma attributes, which themselves =
probably came
>>>> via cut-n-paste from prior drivers.  I can't come up with any =
explanation for that
>>>> which makes good design sense, so I'll agree that storage drivers =
shouldn't
>>>> reference MAXBSIZE.
>>> Should DFLTPHYS be used there?
>>> Or is there a better DMA-specific constant?
>>> Or, perhaps, each driver should just use its won private constant =
based on its
>>> hardware capabilities?
>>=20
>> Each driver should be advertising its own maxio attribute, with the =
exception
>> of CAM drivers.  Advertising is optional in CAM, and is defaulted to =
64k.  But
>> yes, each driver should define and use its own constants here.
>=20
> I actually meant not what drivers advertise but what they use in =
busdma.
> Or are those directly related?
>=20

Yes, the should normally be directly related except in maybe a few very =
rare cases.

Scott