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: Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx>
---
drivers/usb/gadget/udc/aspeed-vhub/ep0.c | 2 ++
drivers/usb/gadget/udc/aspeed-vhub/epn.c | 14 +++++++---
drivers/usb/gadget/udc/aspeed-vhub/vhub.h | 33 +++++++++++++++++++++++
3 files changed, 46 insertions(+), 3 deletions(-)
diff --git a/drivers/usb/gadget/udc/aspeed-vhub/ep0.c b/drivers/usb/gadget/udc/aspeed-vhub/ep0.c
index 44f2b3b53b2f..e2927fb083cf 100644
--- a/drivers/usb/gadget/udc/aspeed-vhub/ep0.c
+++ b/drivers/usb/gadget/udc/aspeed-vhub/ep0.c
@@ -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);
diff --git a/drivers/usb/gadget/udc/aspeed-vhub/epn.c b/drivers/usb/gadget/udc/aspeed-vhub/epn.c
index 80c9feac5147..5939eb1e97f2 100644
--- a/drivers/usb/gadget/udc/aspeed-vhub/epn.c
+++ b/drivers/usb/gadget/udc/aspeed-vhub/epn.c
@@ -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);
diff --git a/drivers/usb/gadget/udc/aspeed-vhub/vhub.h b/drivers/usb/gadget/udc/aspeed-vhub/vhub.h
index 2b040257bc1f..4ed03d33a5a9 100644
--- a/drivers/usb/gadget/udc/aspeed-vhub/vhub.h
+++ b/drivers/usb/gadget/udc/aspeed-vhub/vhub.h
@@ -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);
--
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