At Bootlin, we recently developed from scratch a new Linux driver for the USB Device Controller found in the Renesas RZ/N1 processor. This driver is already accepted upstream, is currently visible in linux-next and should hopefully be part of the upcoming Linux 6.3 release.
As part of developing this driver, we of course had to… test it! To test a USB Device Controller driver, the obvious idea that comes to mind is to use the available USB gadget drivers in the Linux kernel, to expose a USB mass-storage device, a USB network device, etc. However, these existing USB gadget drivers are not necessarily the best option for this kind of testing: they perform some more or less complex transfers and it can be difficult to find the root cause of an error using these gadget drivers.
Fortunately, a tool exists precisely to perform testing of USB transfers: this tool is called testusb
, and it can be found directly in the Linux kernel source code in tools/usb/testusb.c. The tool is quite old and not very well known, but it proved to be very useful for our testing, so in this blog post we are sharing some details on how to use it.
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