Mark Lord wrote:
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.
Not for lba48, which has a larger max-sectors but is still clamped to
the same 256 PRD entries...
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.
Yeah, a couple of Alan's PATA drivers are fixed at 255.
That was in the days before the block layer could limit the segment count.
Ahhhhh, useful to know.
Jeff
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