DMA limits

Forum: The Linux Kernel Hackers' Guide
Re: DMA buffer sizes
Keywords: DMA limit
Date: Sat, 26 Jul 1997 02:16:07 GMT
From: Albert Cahalan <acahalan at cs.uml.edu> <unknown>

> I want to allocate a DMA buffer larger than 128*1024. > Is it possible to configure the kernel to allow bigger > DMA buffer sizes? I've attempted to increase the PAGE_SIZE > to 8192 but that crashes the system. I hope that is not PC hardware! The ISA bus has a hard limit of 128 kB (16-bit DMA) or 64 kB (8-bit). Even 128 kB is hard though, because memory fragmentation makes it unlikely that you can allocate a contiguous 128 kB chunk under the 16 MB ISA DMA limit (or elsewhere).