i.MX ProcessorsのトピックiMX6 kernel page sizes

iMX6 kernel page sizes

GregT — Thu, 19 Jan 2017 14:47:11 GMT

Is it possible to allocate kernel pages larger than 4KB in the linux kernel for the iMX6. I tried turning on the HUKETLBFS Kconfig in our kernel but the unit does not boot now. We want to create a DMA driver than can handle up to 320KB buffers from an FPGA but did not want to create multiple pages then transfer multiple buffers, one for each 4KB page.

Thanks in advance.

Greg

Re: iMX6 kernel page sizes

GregT — Thu, 19 Jan 2017 15:56:49 GMT

So I tried using dma_alloc_coherent with 8MB (0x800000) and it did not fail. Here is the printk from a kernel module I put the allocate in. Can I assume this is 8MB of contiguous memory that the fpga device can dma 8MB of data into?

ALLOCATED dma memory 0x800000 bytes, dma_handle 0x62800000, cpu_addr 0xff100000

Thanks,Greg

Re: iMX6 kernel page sizes

erdani80 — Thu, 19 Jan 2017 16:07:56 GMT

That call must provide consistent memory ( https://www.kernel.org/doc/Documentation/DMA-API.txt ).

Are you connecting the FGPA using PCIe?, is that is the case you could also look at pci_alloc_consistent ( Kernel source: Documentation/DMA-mapping.txt ). We have used this method successfully for FPGA PCIe devices ussing DMA from the FPGA to the iMX6 DDR memory.

Re: iMX6 kernel page sizes

GregT — Thu, 19 Jan 2017 16:51:36 GMT

We are going from an FPGA accross PCIe to the iMX6. For some reason the kernel I'm using does not have pci_alloc_consistent. Its linux 3.14.52-r0. My bad. I used the wrong name. It does have the function.

How large were the DMA buffers you transferred from the FPGA to the iMX6 DDR? Our largest will be about 6.4MB.

Thanks

Re: iMX6 kernel page sizes

erdani80 — Fri, 20 Jan 2017 07:47:11 GMT

We are just moving 1600bytes buffers from the FPGA to the imx6, we have seveal buffers sending data and we are trying to keep latency as low as possible.

If you were able to allocate a 8Meg buffer then there should be no problem to transfer such amount of memory.

We tested our driver against the 3.10 and 4.1 kernel and is an almost unmodified driver we developed for a PC platform. We only had to change DMA target address in the FPGA DMA controller from 64 bits to 32 bits to get it working.