From mboxrd@z Thu Jan 1 00:00:00 1970 References: <87r1efj8mq.fsf@xenomai.org> <10a0-6128f200-125-29fb8780@204573282> From: Philippe Gerum Subject: Re: Doing DMA from peripheral to userland memory In-reply-to: <10a0-6128f200-125-29fb8780@204573282> Date: Fri, 27 Aug 2021 16:36:28 +0200 Message-ID: <87o89jj6oj.fsf@xenomai.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable List-Id: Discussions about the Xenomai project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: =?utf-8?Q?Fran=C3=A7ois?= Legal Cc: xenomai@xenomai.org Fran=C3=A7ois Legal writes: > Le Vendredi, Ao=C3=BBt 27, 2021 15:54 CEST, Philippe Gerum a =C3=A9crit:=20 >=20=20 >>=20 >> Fran=C3=A7ois Legal writes: >>=20 >> > Le Vendredi, Ao=C3=BBt 27, 2021 15:01 CEST, Philippe Gerum a =C3=A9crit:=20 >> >=20=20 >> >>=20 >> >> Fran=C3=A7ois Legal via Xenomai writes: >> >>=20 >> >> > Hello, >> >> > >> >> > working on a zynq7000 target (arm cortex a9), we have a peripheral = that generates loads of data (many kbytes per ms). >> >> > >> >> > We would like to move that data, directly from the peripheral memor= y (the OCM of the SoC) directly to our RT application user memory using DMA. >> >> > >> >> > For one part of the data, we would like the DMA to de interlace tha= t data while moving it. We figured out, the PL330 peripheral on the SoC sho= uld be able to do it, however, we would like, as much as possible, to retai= n the use of one or two channels of the PL330 to plain linux non RT use (vi= a dmaengine). >> >> > >> >> > My first attempt would be to enhance the dmaengine API to add RT AP= I, then implement the RT API calls in the PL330 driver. >> >> > >> >> > What do you think of this approach, and is it achievable at all (DM= A directly to user land memory and/or having DMA channels exploited by xeno= mai and other by linux) ? >> >> > >> >> > Thanks in advance >> >> > >> >> > Fran=C3=A7ois >> >>=20 >> >> As a starting point, you may want to have a look at this document: >> >> https://evlproject.org/core/oob-drivers/dma/ >> >>=20 >> >> This is part of the EVL core documentation, but this is actually a >> >> Dovetail feature. >> >>=20 >> > >> > Well, that's quite what I want to do, so this is very good news that i= t is already available in the future. However, I need it through the ipipe = right now, but I guess the process stays the same (through patching the dma= engine API and the DMA engine driver). >> > >> > I would guess the modifications to the DMA engine driver would be then= easily ported to dovetail ? >> > >>=20 >> Since they should follow the same pattern used for the controllers >> Dovetail currently supports, I think so. You should be able to simplify >> the code when porting it Dovetail actually. >>=20 > > That's what I thought. Thanks a lot. > > So now, regarding the "to userland memory" aspect. I guess I will somehow= have to, in order to make this happen, change the PTE flags to make these = pages non cacheable (using dma_map_page maybe), but I wonder if I have to m= ap the userland pages to kernel space and whether or not I have to pin the = userland pages in memory (I believe mlockall in the userland process does t= hat already) ? > The out-of-band SPI support available from EVL illustrates a possible implementation. This code [2] implements what is described in this page [1]. [1] https://evlproject.org/core/oob-drivers/spi/ [2] https://source.denx.de/Xenomai/xenomai4/linux-evl/-/blob/0969ccef9a5318= 244e484e847dab52999f6fec5c/drivers/spi/spi.c#L4259 --=20 Philippe.