Date: Fri, 14 Dec 2018 18:03:51 -0500 From: Kurt Lidl <lidl@pix.net> To: Alan Somers <asomers@freebsd.org> Cc: Warner Losh <imp@bsdimp.com>, rajfbsd@gmail.com, "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>, freebsd-drivers@freebsd.org Subject: Re: How to use the DMA Engine in FreeBSD? Message-ID: <c98d4aff-851c-1e38-ed64-1f58e0adc9df@pix.net> In-Reply-To: <CAOtMX2jXMz3D8_JvOk4M2DrEZDP8sztgy2bdBuv-yNwz9zR2JQ@mail.gmail.com> References: <CAAO%2BANOty8FeOR7VQdXmxWy5y288pm=Q4cswHJ1BbgT2h1cUWg@mail.gmail.com> <CANCZdfrEv9o6_ydp9Qe73O1v6NqHFtivHpw4m2PKhTyAVaPR9g@mail.gmail.com> <26df913b-a2f8-2709-1cec-d11ad7d113a8@pix.net> <CAOtMX2jXMz3D8_JvOk4M2DrEZDP8sztgy2bdBuv-yNwz9zR2JQ@mail.gmail.com>
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On 12/14/18 11:09 AM, Alan Somers wrote: > On Fri, Dec 14, 2018 at 8:36 AM Kurt Lidl <lidl@pix.net> wrote: >> >> On 12/13/18 10:53 AM, Warner Losh wrote: >>> On Thu, Dec 13, 2018, 3:04 AM Rajesh Kumar <rajfbsd@gmail.com wrote: >>> >>>> Hi, >>>> >>>> Is there any good documentation available to understand the existing >>>> support, API's and how-to use the DMA Engine in FreeBSD? >>>> >>> >>> >>> Usually you just use pci busmastering and it just works. >>> >>> I am trying to write a test driver which will use DMA Engine to do the data >>>> transfer (rather than plain memcpy which involves cpu). Can anyone point >>>> to any driver implementation which has similar functions implemented? I >>>> see references to SYS_RES_DRQ to allocate DMA channels and play around. But >>>> that seems to be specific to ISA. Can it be used for PCI drivers as well? >>>> >>> >>> No. ISA DMA is only for really old hardware without it's own DMA engine. >>> >>> Look at the busdma api/man page. >> >> For some Intel based server hardware, there is the "ioat" driver, which >> allows for user code to schedule DMA operations. See ioat(4) for >> details, including a pointer to the test program. >> >> -Kurt > > ioat(4) looks cool. But the man page is vague on a few points. Do > you know the answers to these questions? > * What happened to ioatcontrol(8)? It's reference by the man page, > but doesn't exist anywhere. root@busybox: locate ioatcontrol /usr/src/tools/tools/ioat/ioatcontrol.8 /usr/src/tools/tools/ioat/ioatcontrol.c > * In what context are callbacks called? Are they called from a signal > handler, or in a separate thread, or something else? I don't know. > * Why isn't ioat.h installed? I don't know that either, but it is in the source tree: root@busybox: locate ioat.h /usr/src/sys/dev/ioat/ioat.h > * Are "interrupts" synonymous with callbacks? > * Do you have a rough idea for about the minimum buffer size that > makes sense to use with ioat? I don't know that either -- I was mostly just pointing out that the facility and driver existed for (some) Intel server hardware. Mostly I'm aware of this because I was surprised when a machine I using this summer started reporting this hardware, and I wasn't familiar with it. Good luck. -Kurt
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