MCIMX8M-EVK kit PCIe Linux Driver

[Tarek]

I am developing a pcie device driver for the iMX8M evaluation kit. The end-point is an FPGA which supports 64-bit DMA and a single MSI interrupt.

First of all in my driver I tried to enable DMA_BIT_MASK(64) using Linux pcie framework API:

pci_set_dma_mask(pdev, DMA_BIT_MASK(64); 

This function is failing and the kernel error message is:

[  +0.008434] Can't support > 32 bit dma.

Second when I tried to enable the pcie interrupt using:

pci_alloc_irq_vectors(pdev, 1, 1, PCI_IRQ_ALL_TYPES);then pci_irq_vector(pdev, 0); this function is returnting Linux IRQ 11.

So when I assign a handler to this IRQ using request_irq() it returns err -22.

(1) Is it possible to enable DMA_BIT_MASK(64)?

(2) Why the kernel is not allowing me to assign an IRQ handler? Is there any PCIe driver example for i.MX8?

Thanks

[mcggoal]

hi, Terak

I have trapped in the same problem: request_irq() return errno -22.

Have you got solution now ?

Thanks !

[igorpadykov]

Hi Tarek

pcie driver example can be found on below link with description in

sect.4.9 PCI Express Root Complex attached Linux Manual.

pci-imx6.c\host\pci\drivers - linux-imx - i.MX Linux kernel 

Best regards
igor
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[Tarek]

Hi Igor,

Thank you for your prompt reply. The document gives a high-level information about the RC and it does not answer my questions.

Also, the PCI driver source is for the root-complex which I don't need to change. What I need to do is implement a device driver for the FPGA which acts as a PCIe end-point and is connected to the M.2 connector on the MX8MDQLQEVK.

To simplify my query:

1. Can the PCIe RC in the IMX8M SoC support 64-bit DMA?
2. How do I enable and assign MSI handler for my end-point?

Thanks for your help

Tarek

[igorpadykov]

Hi Tarek

seems 64-bit is supported as described in sect.11.2.5.1.1

Table 10-1 DMA Module Features i.MX8MDQ Reference Manual
https://www.nxp.com/docs/en/reference-manual/IMX8MDQLQRM.pdf

>How do I enable and assign MSI handler for my end-point?

please refer to common linux tutorials

MSI-HOWTO.txt [LWN.net] 

MSI Register for pcie device driver - Stack Overflow 

Best regards
igor

[Tarek]

Hi Igor,

If i.MX8M supports 64-bit why is it forced to 32 in fsl-imx8mq.dtsi file?

dma_cap: dma_cap {
compatible = "dma-capability";
only-dma-mask32 = <1>;
};

fsl-imx8mq.dtsi\freescale\dts\boot\arm64\arch - linux-imx - i.MX Linux kernel 

Because of this device tree setting the kernel will not accept setting the DMA mask to 64-bit and gives this error:

[  +0.008434] Can't support > 32 bit dma

Can you please confirm that removing this line: "only-dma-mask32 = <1>;" will work fine and not cause any issues?

Thanks,

Tarek

[igorpadykov]

Hi Tarek

I escalated your question internally and received answer:

--------------------------

The internal bus is HW limited to 32-bits. That is why the cap is 32 bits.

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Best regards
igor