drivers: usb: udc: skeleton: handle special case of set_halt() for EP0 (5bef4a9d) · Commits · Wenxi XU / zephyr

The UDC stack assumes that 'halt' on control endpoints is automatically cleared by device drivers and never calls udc_ep_clear_halt() for such endpoints. In practice, most controllers do perform this automatic clear in hardware, but this requires special handling in udc_ep_set_halt() for control endpoints (EP0), as setting the 'halted' bit on such endpoints will lead to the software getting out-of-sync with the hardware. Update the UDC skeleton driver to handle this edge case and add a comment documenting the stack's behavior, along with the hardware behavior expected by the code added to the skeleton driver for it to be functional. Co-authored-by:

Johann Fischer <johann.fischer@nordicsemi.no> Signed-off-by:

Mathieu CHOPLAIN <mathieu.choplain-ext@st.com>

drivers/usb/udc/udc_skeleton.c

+20 −0

Changes for drivers/usb/udc/udc_skeleton.c: 20 added lines, 0 removed lines.
Original line number	Diff line number	Diff line
		@@ -160,7 +160,27 @@ static int udc_skeleton_ep_set_halt(const struct device *dev,
		{
		LOG_DBG("Set halt ep 0x%02x", cfg->addr);

		/*
		* NOTE: udc_ep_clear_halt() is not called for control endpoints.
		*
		* When an endpoint is halted or a control pipe request is not
		* supported, endpoint responds with a STALL handshake packet. The
		* specification distinguishes between a functional stall and a
		* protocol stall. The stack calls udc_ep_set_halt() to set a
		* functional or protocol stall. A protocol stall is unique to control
		* pipes and terminates at the beginning of the next control transfer.
		* Although a control pipe may support functional stall, it is not
		* recommended by the specification. The stack does not call
		* udc_ep_clear_halt() for control endpoints.
		*
		* How a driver clears a protocol stall depends on the implementation.
		* Some controllers automatically clear the protocol stall condition
		* when the next setup packet arrives, while others require software
		* intervention.
		*/
		if (USB_EP_GET_IDX(cfg->addr) != 0U) {
		cfg->stat.halted = true;
		}

		return 0;
		}

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