imx8mm pcie ref clock

[qssms]

Hi,

I develop a board based on IMX8MM.

Board is var-som-mx8m-mini.

This board is connected to intel ethernet controller i210-AT chip.

then, this chip is connected to PCIE#A_REFCLK100M_N, PCIE#A_REFCLK100M_P.

But, I can not use this signal. clock output of this pin is nothing.

How to use a reference clock output for PCIE?

Is this possible to use?

Thanks.

[marcelziswiler]

> this is not recommended

What exactly do you mean? Supposedly, this has been validated by NXP, not?

[igorpadykov]

Hi seungmin

recommended to use external clock as described in Table 9. PCIe recommendations

i.MX 8M Mini Hardware Developer’s Guide

and follow i.MX8M Mini EVK schematic

i.MX 8M Mini Evaluation Kit LPDDR4 Design Files

Best regards
igor
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[qssms]

Thanks for your kind response.

I was receipt your board developer's guide. and it was very useful.

but, I want to know how to enable the PCIe clock.

default boot kernel image is disenabled PCIe ref clock output.

is there possible to use this pin to output clock by kernel edit?

Thanks.

shin

[igorpadykov]

this is not recommended, how ever one can try to enable it using

IOMUXC_GPR_GPR14 (check its description in Reference Manual).

Please look at function imx_pcie_enable_ref_clk() in imx6-pcie.c

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

clk driver

clk-imx8mm.c\imx\clk\drivers - linux-imx - i.MX Linux kernel 

Best regards
igor

[qssms]

I know that is not recommended. but I want to know my schemetic is the right thing for just test.

I write further my question below.

1. my kernel version of i.MX8 mini is imx_4.14.98 2.0.0_ga. but your kernel version of the response function is imx_4.19.35_1.1.0. this function isn't matching my kernel version. how to edit in imx_4.14.98_2.0.0_ga?

2. I used the yocto project to i.MX8 mini. and use bitbake. is it possible to edit to use bitbake - menuconfig?

thanks

shin

[igorpadykov]

for L4.14.98 2.0.0 it is :

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

Best regards
igor