Linux Kernel Renesas USBHS Driver Unbind Synchronization Issue Causes Synchronous External Abort

A synchronization issue in the Renesas USBHS driver for the Linux kernel can lead to a synchronous external abort on the Renesas RZ/G3S SoC. This problem occurs when the 'unbind' operation is executed after a specific configuration sequence, which includes setting up a USB gadget with the Ethernet function. The issue arises because the 'usbhs_sys_function_pullup' function, which interacts with the USB hardware registers, is called after the USBHS clocks have been turned off. This bus error is expected when a master tries to access a module whose clock has been stopped, a scenario that can be triggered by the recent changes in the clock management APIs. The problem can be reproduced by manually unbinding a USB gadget after it has been configured and activated, which disrupts the expected operation and causes a bus error.

Impact

The unbinding process of USB gadgets can cause a bus error, disrupting normal operations and potentially leading to system instability.

Reproduction

To reproduce this issue, load the necessary USB functions and composite drivers, then create a USB gadget configuration that includes the Ethernet function. After the gadget is set up, manually unbind it using the appropriate platform driver command. This sequence will trigger a synchronous external abort error on the Renesas RZ/G3S SoC.

Remediation

The USBHS clocks should be disabled at the end of the remove process in the driver, ensuring that no operations are attempted on the hardware after the clocks have been turned off.