(in)appropriate uses for MAXBSIZE

[Scott Long]

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:
>> 
>>> 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?
>> 
>> 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.
> 
> I actually meant not what drivers advertise but what they use in busdma.
> Or are those directly related?
> 

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

Scott