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SubjectRe: [PATCH] MIPS: Fix `dma_alloc_coherent' returning a non-coherent allocation
On Thu, 1 Nov 2018, Christoph Hellwig wrote:

> Oops, yes this looks good:

BTW, for anyone missing hardware suitable for serious DMA testing I can
recommend getting a pair of DEFPA cards, the ubiquitous PCI version of
this board, cheaply available, which is the same except for a different
host bus bridge ASIC, developed later. They can be wired back to back
similarly to Ethernet adapters (or in a loop if you have 2 or more dual
attachment versions), no other hardware is required save for patch cords.
Version 3 (DEFPA-xC) boards support universal PCI signalling, older ones
are 5V-only.

These devices are a stellar example of fine engineering[1]. Our `defxx'
driver, which I believe has been adapted from the DEC OSF/1 one referred
in the said document, has some latency and other issues that I plan to
address sometime, once I have sorted higher-priority issues, however
hardware itself is excellent.

References:

[1] Chran-Ham Chang et al., "High-performance TCP/IP and UDP/IP Networking
in DEC OSF/1 for Alpha AXP", Digital Technical Journal, vol. 5, no. 1
(Winter 1993), "Network Adapter Characteristics", p. 7
<ftp://ftp.linux-mips.org/pub/linux/mips/people/macro/DEC/DTJ/DTJ904/DTJ904PF.PDF>

Maciej

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