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. François > [1] https://evlproject.org/core/oob-drivers/spi/ > [2] > https://source.denx.de/Xenomai/xenomai4/linux-evl/-/blob/0969ccef9a5318244e484e847dab52999f6fec5c/drivers/spi/spi.c#L4259 > > -- > Philippe.
