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Commit bb286336 authored by Benjamin Herrenschmidt's avatar Benjamin Herrenschmidt Committed by Felipe Balbi
Browse files

usb: gadget: aspeed: Workaround memory ordering issue 



The Aspeed SoC has a memory ordering issue that (thankfully)
only affects the USB gadget device. A read back is necessary
after writing to memory and before letting the device DMA
from it.

Signed-off-by: default avatarBenjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: default avatarFelipe Balbi <felipe.balbi@linux.intel.com>
parent 9566a7c7

drivers/usb/gadget/udc/aspeed-vhub/ep0.c

+2 −0
Original line number Diff line number Diff line
@@ -219,6 +219,8 @@ static void ast_vhub_ep0_do_send(struct ast_vhub_ep *ep, 
	if (chunk && req->req.buf)

		memcpy(ep->buf, req->req.buf + req->req.actual, chunk);



	vhub_dma_workaround(ep->buf);



	/* Remember chunk size and trigger send */

	reg = VHUB_EP0_SET_TX_LEN(chunk);

	writel(reg, ep->ep0.ctlstat);

drivers/usb/gadget/udc/aspeed-vhub/epn.c

+11 −3
Original line number Diff line number Diff line
@@ -66,11 +66,16 @@ static void ast_vhub_epn_kick(struct ast_vhub_ep *ep, struct ast_vhub_req *req) 
	if (!req->req.dma) {



		/* For IN transfers, copy data over first */

		if (ep->epn.is_in)

		if (ep->epn.is_in) {

			memcpy(ep->buf, req->req.buf + act, chunk);

			vhub_dma_workaround(ep->buf);

		}

		writel(ep->buf_dma, ep->epn.regs + AST_VHUB_EP_DESC_BASE);

	} else

	} else {

		if (ep->epn.is_in)

			vhub_dma_workaround(req->req.buf);

		writel(req->req.dma + act, ep->epn.regs + AST_VHUB_EP_DESC_BASE);

	}



	/* Start DMA */

	req->active = true;
@@ -161,6 +166,7 @@ static inline unsigned int ast_vhub_count_free_descs(struct ast_vhub_ep *ep) 
static void ast_vhub_epn_kick_desc(struct ast_vhub_ep *ep,

				   struct ast_vhub_req *req)

{

	struct ast_vhub_desc *desc = NULL;

	unsigned int act = req->act_count;

	unsigned int len = req->req.length;

	unsigned int chunk;
@@ -177,7 +183,6 @@ static void ast_vhub_epn_kick_desc(struct ast_vhub_ep *ep, 


	/* While we can create descriptors */

	while (ast_vhub_count_free_descs(ep) && req->last_desc < 0) {

		struct ast_vhub_desc *desc;

		unsigned int d_num;



		/* Grab next free descriptor */
@@ -227,6 +232,9 @@ static void ast_vhub_epn_kick_desc(struct ast_vhub_ep *ep, 
		req->act_count = act = act + chunk;

	}



	if (likely(desc))

		vhub_dma_workaround(desc);



	/* Tell HW about new descriptors */

	writel(VHUB_EP_DMA_SET_CPU_WPTR(ep->epn.d_next),

	       ep->epn.regs + AST_VHUB_EP_DESC_STATUS);

drivers/usb/gadget/udc/aspeed-vhub/vhub.h

+33 −0
Original line number Diff line number Diff line
@@ -462,6 +462,39 @@ enum std_req_rc { 
#define DDBG(d, fmt, ...)	do { } while(0)

#endif



static inline void vhub_dma_workaround(void *addr)

{

	/*

	 * This works around a confirmed HW issue with the Aspeed chip.

	 *

	 * The core uses a different bus to memory than the AHB going to

	 * the USB device controller. Due to the latter having a higher

	 * priority than the core for arbitration on that bus, it's

	 * possible for an MMIO to the device, followed by a DMA by the

	 * device from memory to all be performed and services before

	 * a previous store to memory gets completed.

	 *

	 * This the following scenario can happen:

	 *

	 *    - Driver writes to a DMA descriptor (Mbus)

	 *    - Driver writes to the MMIO register to start the DMA (AHB)

	 *    - The gadget sees the second write and sends a read of the

	 *      descriptor to the memory controller (Mbus)

	 *    - The gadget hits memory before the descriptor write

	 *      causing it to read an obsolete value.

	 *

	 * Thankfully the problem is limited to the USB gadget device, other

	 * masters in the SoC all have a lower priority than the core, thus

	 * ensuring that the store by the core arrives first.

	 *

	 * The workaround consists of using a dummy read of the memory before

	 * doing the MMIO writes. This will ensure that the previous writes

	 * have been "pushed out".

	 */

	mb();

	(void)__raw_readl((void __iomem *)addr);

}



/* core.c */

void ast_vhub_done(struct ast_vhub_ep *ep, struct ast_vhub_req *req,

		   int status);