How to improve the USB OTG speed of STM32MP157?

[JYan.17]

The hardware is STM32MP157C-DK2 board.

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1. We setup the test environment as below:

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We bridge the USB port and the Ethernet port in the ST.

The throughput is about 270Mbit/sec(Limited by the usb to Ethernet convertor).

2. Another test environment is:

The ST is using the USB gadget functions. The USB port and the Ethernet port are bridged.

Result:

​RNDIS: 90Mbit/sec.

CDC-EEM: 110Mbit/sec.

CDC-ECM: 135Mbit/sec.

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The performance is not good enough compared to test1.

Is the speed limited by the USB-OTG controller(dwc2)?

Can we change the DMA settings in the dwc2 ?

Or anyway to improve the throughput?

Please help!

Thank you very much.

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[Christophe Guibout]

Hi,

The way to improve the throughput is to tune FIFO size in the OTG IP. It can be done through kernel device tree.

In usbotg_hs entry of arch/arm/boot/dts/stm32mp157c.dtsi :

usbotg_hs: usb-otg@49000000 {
	compatible = "st,stm32mp1-hsotg", "snps,dwc2";
	reg = <0x49000000 0x10000>;
	clocks = <&rcc USBO_K>;
	clock-names = "otg";
	resets = <&rcc USBO_R>;
	reset-names = "dwc2";
	interrupts-extended = <&intc GIC_SPI 98 IRQ_TYPE_LEVEL_HIGH>,
			 <&exti 44 1>;
	interrupt-names = "event", "wakeup";
	g-rx-fifo-size = <256>;
	g-np-tx-fifo-size = <32>;
	g-tx-fifo-size = <128 128 64 64 64 64 32 32>;
	dr_mode = "otg";
	usb33d-supply = <&usb33>;
	power-domains = <&pd_core>;
	wakeup-source;
	status = "disabled";
};

The following patch increases tx troughput (I measured a gain of 12% in TX):

- g-np-tx-fifo-size = <32>;
- g-tx-fifo-size = <128 128 64 64 64 64 32 32>;
+ g-np-tx-fifo-size = <256>;
+ g-tx-fifo-size = <128 128 64 16 16 16 16 16>

The sum of all FIFO size must be lower than 952.

Depending on your use case, you can tune FIFO sizes to get the best compromise.

BR,

Christophe