Merge branches 'work.misc' and 'work.dcache' of git://git.kernel.org/pub/scm/linux...

[sfrench/cifs-2.6.git] / drivers / usb / gadget / udc / aspeed-vhub / vhub.h

diff --git a/drivers/usb/gadget/udc/aspeed-vhub/vhub.h b/drivers/usb/gadget/udc/aspeed-vhub/vhub.h
index 2b040257bc1f698f0097a4d673ed6cb9fffe3d6b..4ed03d33a5a92b53f836d9d6930722aa5c418cfe 100644 (file)
--- 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);