Re: [PATCH] IDE 58

Benjamin Herrenschmidt
2002-05-08T20:36:05Z

>> I though about that, but what about corner cases where only a single
>> register can be accessed ? (typically alt status). Provide specific
>> routines ? Also, how does the extended addressing works ? by writing
>> several times to the cyl registers ? That would have to be dealt with
>> as well in each host driver then.
>
>There are lots of cases we don't care about speed - things like setup of
>the controller, changing UDMA mode etc.

Right, so we keep the basic indiret access functions, and add the taskfile
ones on top for performances, that's what you mean ?

>> Right. We could go the darwin (apple) way and have taskfile_load/store
>> functions doing the entire registers controlled by a bitmask of which
>> registers has to be touched. it has a cost (testing each bit and
>> conditionally branching, which can suck hard) but probably less than
>
>Get yourself a conditional move instruction 8)

Hehe, let's make an ARM/PPC hybrid ;)

>> an indirect function call which isn't predictable.
>
>Or you have a small set of such functions for the critical paths - ie doing
>actual block I/O which pass the set of values required to do that operation
>and do the stores. What are the performance critical paths
>
> Begin a disk write
> Begin a disk read
> PIO transfer in
> PIO transfer out
> End a disk I/O fastpaths (no error case)
>
> Maybe ATAPI command writes ?
>
>beyond that I doubt the rest are critical

Well, I would normally agree with the above... except that IDE is so full of
corner cases that I don't want to see dealt with in each host controller
driver...

Ben.