Merge pull request #5720 from kjbracey-arm/STM32F7_DMB

Add memory barriers to STM32F7xx Ethernet

Author: 0xc0170

targets/TARGET_STM/TARGET_STM32F7/device/stm32f7xx_hal_eth.c

@@ -717,6 +717,8 @@ HAL_StatusTypeDef HAL_ETH_TransmitFrame(ETH_HandleTypeDef *heth, uint32_t FrameL
     heth->TxDesc->Status |=ETH_DMATXDESC_FS|ETH_DMATXDESC_LS;
     /* Set frame size */
     heth->TxDesc->ControlBufferSize = (FrameLength & ETH_DMATXDESC_TBS1);
+    /* Ensure rest of descriptor is written to RAM before the OWN bit */
+    __DMB();
     /* Set Own bit of the Tx descriptor Status: gives the buffer back to ETHERNET DMA */
     heth->TxDesc->Status |= ETH_DMATXDESC_OWN;
     /* Point to next descriptor */
@@ -746,13 +748,18 @@ HAL_StatusTypeDef HAL_ETH_TransmitFrame(ETH_HandleTypeDef *heth, uint32_t FrameL
         heth->TxDesc->ControlBufferSize = (size & ETH_DMATXDESC_TBS1);
       }
 
+      /* Ensure rest of descriptor is written to RAM before the OWN bit */
+      __DMB();
       /* Set Own bit of the Tx descriptor Status: gives the buffer back to ETHERNET DMA */
       heth->TxDesc->Status |= ETH_DMATXDESC_OWN;
       /* point to next descriptor */
       heth->TxDesc = (ETH_DMADescTypeDef *)(heth->TxDesc->Buffer2NextDescAddr);
     }
   }
 
+  /* Ensure all descriptors are written to RAM before checking transmitter status */
+  __DMB();
+
   /* When Tx Buffer unavailable flag is set: clear it and resume transmission */
   if (((heth->Instance)->DMASR & ETH_DMASR_TBUS) != (uint32_t)RESET)
   {