topic Re: DMA for PCIe on i.MX 8M Plus & Mini in i.MX Processors

DMA for PCIe on i.MX 8M Plus & Mini

mandre — Thu, 27 Jun 2024 14:41:37 GMT

Hello

I am trying to use a DMA inside the i.MX 8M to perform write transactions to a PCIe endpoint. We haven’t fully decided yet between the i.MX 8M Mini and i.MX 8M Plus, I would appreciate if both of those processors could be considered in the answer.

I understand from the Processor Reference Manuals and forum posts that the SDMA cannot be used for this, but the manual refers to an "Embedded DMA" (IMX8MPRM chapter 11.4.2.4). I can't see any such DMA engine registered within the Linux subsystem. dma_request_channel() only returns SDMA channels, same in the sysfs. I can't see any reference to a DMA in pci-imx6.c (driver used for i.MX 8 as well).

The “AN13164 - iMX8MP PCIe Bandwidth Analysis” calls out that a DMA transfer is used, but no source code is provided. There is also a community thread about this: https://community.nxp.com/t5/i-MX-Processors/iMX8M-Plus-PCIe-DMA-Feature/td-p/1529555. Linux v5.4.70 (version used for AN13164) doesn't have any reference to DMA in pcitest.c or pci-epf-test.c. Also, I can't find any function called imx6_pcie_local_dma_start() as indicated in the community thread above in any version of mainline Linux.

A post about a similar test on the i.MX6 (https://community.nxp.com/t5/i-MX-Processors-Knowledge-Base/i-MX6Q-PCIe-EP-RC-Validation-System/ta-p/1126624) refers that the IPU was used for the DMA transfer, but the i.MX 8M doesn't have any such IPU.

I also can't find any reference to a DMA for PCIe in the Linux Reference Manual.

My questions:

How can we use a DMA engine of the i.MX 8M (Plus/Mini) to transfer data from the system DDR memory to a PCIe endpoint device? Do you have any Linux driver for this? Any examples?
Can you provide the exact source code & scripts & command line that were used for AN13164 generate those test results? Which DMA engine was used?

Re: DMA for PCIe on i.MX 8M Plus & Mini

joanxie — Fri, 28 Jun 2024 07:24:46 GMT

mail to you, pls check

Re: DMA for PCIe on i.MX 8M Plus & Mini

mandre — Wed, 03 Jul 2024 07:06:54 GMT

I replied to your email on Friday, please check. Haven't heard back yet.

Re: DMA for PCIe on i.MX 8M Plus & Mini

karina_valencia — Wed, 10 Jul 2024 16:53:42 GMT

@joanxie please continue with the follow-up.

Re: DMA for PCIe on i.MX 8M Plus & Mini

joanxie — Thu, 11 Jul 2024 00:29:16 GMT

I already replied to the customer via mail, because I couldn't access the community last week

Re: DMA for PCIe on i.MX 8M Plus & Mini

mandre — Thu, 11 Jul 2024 05:27:42 GMT

Please check your support ticket #0062962

You did reply answering 1 of my 4 questions on June 28, 7:23am via the NXP support ticketing system. I replied to this on June 28, 9:13am with a follow-up question and the the re-iteration of the un-answered questions.

I haven't heard since (neither publicly on the forum nor via the support ticket).

Re: DMA for PCIe on i.MX 8M Plus & Mini

joanxie — Thu, 11 Jul 2024 06:15:51 GMT

I just mailed to you attach my previous reply, as I mentioned, I couldn't access the community last week, I mailed to you, maybe the system issue, I screen shot it, you can check, I'm waiting for you cable and test result

Re: DMA for PCIe on i.MX 8M Plus & Mini

svolpe — Tue, 27 Aug 2024 23:04:21 GMT

I'm also trying to get a DMA reading the data off of the pcie bus. Can you post here or message me on how you got it working? Or can someone from nxp give me info on the solution?

Re: DMA for PCIe on i.MX 8M Plus & Mini

mandre — Wed, 28 Aug 2024 00:22:53 GMT

Some driver support got added in mainline Kernel v6.3. You can use the pcitest tool (part of the Kernel) as example.

Re: DMA for PCIe on i.MX 8M Plus & Mini

svolpe — Wed, 28 Aug 2024 00:30:12 GMT

one quick question: I'm assuming there is no "generic pci-e DMA" driver and that I need to write my own kernel module to do the DMA stuff on the PCIe interface? Or is there a kernel module already in existence that handles the DMA?

Re: DMA for PCIe on i.MX 8M Plus & Mini

mandre — Wed, 28 Aug 2024 00:51:09 GMT

You'll likely have to write some Kernel driver by yourself.

Re: DMA for PCIe on i.MX 8M Plus & Mini

radhak4x — Wed, 26 Mar 2025 14:35:19 GMT

Hi Mandre..!
https://community.nxp.com/t5/Other-NXP-Products/How-to-Enable-DMA-for-USB-for-IMX8M-Plus-based-on-Linux-kernel-6/m-p/2064737

i also see some references to DMA embedded controller already in, but i dont see any such reference from imx8M Reference manual.

i want to enable DMA for USB for better throughputs with high CPU usage.

does this is already implemented? if see could you please share reference to that from any github reference.

i see configurations are already enabled for EHCI related.

please suggest..! thanks

Re: DMA for PCIe on i.MX 8M Plus & Mini

radhak4x — Wed, 26 Mar 2025 14:36:07 GMT

Hi Mandre..!
https://community.nxp.com/t5/Other-NXP-Products/How-to-Enable-DMA-for-USB-for-IMX8M-Plus-based-on-Linux-kernel-6/m-p/2064737

i also see some references to DMA embedded controller already in, but i dont see any such reference from imx8M Reference manual.

i want to enable DMA for USB for better throughputs with high CPU usage.

does this is already implemented? if see could you please share reference to that from any github reference.

i see configurations are already enabled for EHCI related.

please suggest..! thanks

Re: DMA for PCIe on i.MX 8M Plus & Mini

mandre — Wed, 26 Mar 2025 17:19:27 GMT

I cannot help on this.

I was using the DMA engine which is part of the PCIe submodule. This is specifically just for PCIe.