AM67A: How to generate PCIe RESET?

Stephen Turner

Genius 3476 points

Part Number: AM67A
Other Parts Discussed in Thread: AM67

Hi,

Wit the AM67A, how does TI recommend we generate a PCIe RESET signal?.

thanks

over 1 year ago

0 Praveen Rao over 1 year ago

TI__Mastermind 48273 points

Hello Stephen,

Our expert who handles PCIe is on out of office till Apr 19th. Please expect reponse once he is back.

Thanks.

0 Takuma Fujiwara over 1 year ago in reply to Praveen Rao

TI__Guru 51863 points

Hi Stephen,

If the purpose is to simulate taking out a PCIe add-in card and then re-enumerating, you can use commandline to:

To remove a PCIe device with domain number 0000, bus number 00, device number 00, and function 0: echo 1 > /sys/bus/pci/devices/0000\:00\:00.0/remove
To rescan the removed device: echo 1 > /sys/bus/pci/rescan

Regards,

Takuma

0 Stephen Turner over 1 year ago in reply to Takuma Fujiwara

Genius 3476 points

Hi Takuma,

The purpose of generating the PERST- signal is to keep any PCIe peripherals in an reset state until the PCIe bus (i.e the AM67 SERDES) is up and running. With the J721e (which I'm familiar) this was done using a GPIO.

On further examination of the J722s EVM, I see that the reset is generated from a GPIO (GPIO Expander - 1 Part # TCA6424ARGJR - port P22 ). So I guess I just need to find where in the Linux PCIe driver this port is manipulated and translate that to my design (using a SoC GPIO port).

thanks

0 Takuma Fujiwara over 1 year ago in reply to Stephen Turner

TI__Guru 51863 points

Hi Stephen,

Understood. To help you with your port, in our dts file, this line is where the PERST signal is connected to our driver: https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/arch/arm64/boot/dts/ti/k3-j722s-evm.dts?h=ti-linux-6.1.y#n877

And the expander is defined here: https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/arch/arm64/boot/dts/ti/k3-j722s-evm.dts?h=ti-linux-6.1.y#n451.

And it is consumed here: https://git.ti.com/cgit/ti-linux-kernel/ti-linux-kernel/tree/drivers/pci/controller/cadence/pci-j721e-host.c?h=ti-linux-6.1.y#n374.

Regards,

Takuma

0 Stephen Turner over 1 year ago in reply to Takuma Fujiwara

Genius 3476 points

Thanks - that helps a lot. Just to confirm that the j721e pcie host code is used in the J722s? (make sense as they are probably using the same PCIe peripheral block)

+1 Takuma Fujiwara over 1 year ago in reply to Stephen Turner

TI__Guru 51863 points

Hi Stephen,

Yes.

Regards,

Takuma

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AM67A: How to generate PCIe RESET?