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    SubjectRe: [2.5] DAC960
    On Sun, Sep 15 2002, Daniel Phillips wrote:
    > On Tuesday 10 September 2002 08:20, Jens Axboe wrote:
    > > On Tue, Sep 10 2002, Samium Gromoff wrote:
    > > > Hello folks, i`m looking at the DAC960 driver and i have
    > > > realised its implemented at the block layer, bypassing SCSI.
    > > >
    > > > So given i have some motivation to have a working 2.5 DAC960
    > > > driver (i have one, being my only controller)
    > > > i`m kinda pondering the matter.
    > > >
    > > > Questions:
    > > > 1. Whether we need the thing to be ported to SCSI
    > > > layer, as opposed to leaving it being a generic block device? (i suppose yes)
    > >
    > > No
    > A somewhat curt reply, it could be seen as a brush-off. I believe the
    > whole story goes something like this: the scsi system is a festering
    > sore on the whole and eventually needs to be rationalized. But until
    > that happens, we should basically just keep nursing along the various
    > drivers that should be using a generic interface, until there really
    > is a generic interface around worth putting in the effort to port to.

    Please, the scsi sub system is not a 'festering sore'. Have you even
    taken a decent look at it, or just spreading the usual "I heard SCSI
    dizzed somwhere" fud? Sure there's room for improvement, 2.5 has in fact
    already gotten quite a lot. It's not perfect and there's still stuff
    that can be cleaned up, but that doesn't mean it's crap.

    > Linus indicated at the Kernel Summit that he'd like to see a
    > cleaned-up scsi midlayer used as framework for *all* disk IO,
    > including IDE. Obviously, what with IDE transitions and whatnot, we
    > are far from being ready to attempt that, so see "nursing along"
    > above. There's no longer any chance that a generic disk midlayer is
    > going to happen in this cycle, as far as I can see. Still, anybody
    > who is interested would do well by studing the issues, and fixing
    > broken drivers certainly qualifies as a way to come up to speed.

    First of all, I believe Linus' plan is to push more functionality into
    the block layer. Generic functionality. And in fact a lot of has already
    happened there, but one does need to pay attention to that sort of thing
    instead of just assuming spouting fud. Examples:

    - queue merge and dma mappings. this is all generic block/bio
    functionality now. please compare scsi_merge.c between 2.4 and
    2.5, if you care to.

    - highmem bounceless operation also added the possibilty to do
    isa bouncing generically in 2.5. this is also gone from scsi.

    - request tagging. 2.5 has a generic implementation, scsi
    transition is not complete though.

    that's just off the top of my head.

    So where am I going with this? I said "don't bother" to the question of
    studying SCSI code, and I stand by that 100%. It would be an absolute
    _waste of time_ if the goal is to make dac960 work in 2.5. I believe why
    should be pretty obvious now.

    Daniel, your (seen before) 'clarification' posts are not.

    > > > 2. Which 2.5 SCSI driver should i use as a start of learning?
    > >
    > > Don't bother
    > Ah, a little harsh. I'd say: study the DAC960 driver, study the
    > scsi midlayer, and study the new bio interface. That's what I'm
    > doing.

    My advise is: take a look at the transition of other drivers, forget
    scsi. Study of bio goes hand in hand with learning from transition of
    other drivers. And note that a reasonable update of dac960 should remove
    3x as much code as it adds, at least.

    I can only note that so far there has been a lot of talk about dac960
    and updating it, and that's about it. Talk/code ratio is very very low,
    I'm tempted to just do the update myself. Might even safe some time.

    Jens Axboe

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