Date: Fri, 14 Dec 2018 09:09:17 -0700 From: Alan Somers <asomers@freebsd.org> To: Kurt Lidl <lidl@pix.net> 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: <CAOtMX2jXMz3D8_JvOk4M2DrEZDP8sztgy2bdBuv-yNwz9zR2JQ@mail.gmail.com> In-Reply-To: <26df913b-a2f8-2709-1cec-d11ad7d113a8@pix.net> References: <CAAO%2BANOty8FeOR7VQdXmxWy5y288pm=Q4cswHJ1BbgT2h1cUWg@mail.gmail.com> <CANCZdfrEv9o6_ydp9Qe73O1v6NqHFtivHpw4m2PKhTyAVaPR9g@mail.gmail.com> <26df913b-a2f8-2709-1cec-d11ad7d113a8@pix.net>
next in thread | previous in thread | raw e-mail | index | archive | help
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. * In what context are callbacks called? Are they called from a signal handler, or in a separate thread, or something else? * Why isn't ioat.h installed? * Are "interrupts" synonymous with callbacks? * Do you have a rough idea for about the minimum buffer size that makes sense to use with ioat? -Alan
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?CAOtMX2jXMz3D8_JvOk4M2DrEZDP8sztgy2bdBuv-yNwz9zR2JQ>