Re: jgarzik and max-sectors: out of memory

[Mark Lord <liml@rtr.ca>]

Jeff Garzik wrote:
..
> Further -- someone with a long ATA memory correct me -- I think that we 
> can increase ATA_MAX_PRD beyond 256.  Most DMA engines should just keep 
> chugging along, provided that we continue to respect the 64k IDE DMA 
> boundaries.

MAX_PRD used to be equal to MAX_SECTORS, as that's the worst case scenario.
The only real gotcha I remember from the original IDE driver,
was that some (very few) controllers were buggy with handing
of a sector_count of zero (256), so setting the limit to a slightly
lower value prevented that from ever being a problem.

That was in the days before the block layer could limit the segment count.

I don't remember which chipsets had the bug; TRM290 was one,
but that never really worked well anyway, and nobody other than
myself seemed to have one of those cards.  Mmm.. Possibly the
Pacific Digital ADMA-100 here as well.. I can look that one up
if I can find the old box full of cards/docs..

Cheers