François Legal <[email protected]> writes:
> Le Vendredi, Août 27, 2021 16:36 CEST, Philippe Gerum <[email protected]> a > écrit: > >> >> François Legal <[email protected]> writes: >> >> > Le Vendredi, Août 27, 2021 15:54 CEST, Philippe Gerum <[email protected]> a >> > écrit: >> > >> >> >> >> François Legal <[email protected]> writes: >> >> >> >> > Le Vendredi, Août 27, 2021 15:01 CEST, Philippe Gerum >> >> > <[email protected]> a écrit: >> >> > >> >> >> >> >> >> François Legal via Xenomai <[email protected]> writes: >> >> >> >> >> >> > 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 memory >> >> >> > (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 that >> >> >> > data while moving it. We figured out, the PL330 peripheral on the >> >> >> > SoC should be able to do it, however, we would like, as much as >> >> >> > possible, to retain the use of one or two channels of the PL330 to >> >> >> > plain linux non RT use (via dmaengine). >> >> >> > >> >> >> > My first attempt would be to enhance the dmaengine API to add RT >> >> >> > API, then implement the RT API calls in the PL330 driver. >> >> >> > >> >> >> > What do you think of this approach, and is it achievable at all (DMA >> >> >> > directly to user land memory and/or having DMA channels exploited by >> >> >> > xenomai and other by linux) ? >> >> >> > >> >> >> > Thanks in advance >> >> >> > >> >> >> > François >> >> >> >> >> >> As a starting point, you may want to have a look at this document: >> >> >> https://evlproject.org/core/oob-drivers/dma/ >> >> >> >> >> >> This is part of the EVL core documentation, but this is actually a >> >> >> Dovetail feature. >> >> >> >> >> > >> >> > Well, that's quite what I want to do, so this is very good news that it >> >> > 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 dmaengine API and the DMA engine driver). >> >> > >> >> > I would guess the modifications to the DMA engine driver would be then >> >> > easily ported to dovetail ? >> >> > >> >> >> >> 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. >> >> >> > >> > 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 >> > map 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 that 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]. >> > > Thanks for the example. I think what I'm trying to do is a little different > from this however. > For the records, this is what I do (and that seems to be working) : > - as soon as user land buffers are allocated, tell the driver to pin the user > land buffer pages in memory (with get_user_pages_fast). I'm not sure if this > is required, as I think mlockall in the app would already take care of that. > - whenever I need to transfer data to the user land buffer, instruct the > driver to dma remap those user land pages (with dma_map_page), then instruct > the DMA controller of the physical address of these pages. > et voilà > > This seem to work correctly and repeatedly so far. > Are transfers controlled from the real-time stage, and if so, how do you deal with cache maintenance between transfers? -- Philippe.
