Re: [PATCH] MIPS: Fix `dma_alloc_coherent' returning a non-coherent allocation

[Maciej W. Rozycki]

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