net: fec_mxc: allow use with cache enabled

Ensure that transmit and receive buffers are cache-line aligned.
Invalidate cache for each packet as received, update receive buffer
descriptors one cache line at a time, flush cache before transmitting.

Original patch by Marek:
 http://lists.denx.de/pipermail/u-boot/2012-February/117695.html

Signed-off-by: Eric Nelson <eric.nelson at boundarydevices.com>
Acked-by: Marek Vasut <marex@denx.de>
Tested-by: Marek Vasut <marex@denx.de>

drivers/net/fec_mxc.c

@@ -50,6 +50,18 @@ DECLARE_GLOBAL_DATA_PTR;
 #define CONFIG_FEC_MXC_SWAP_PACKET
 #endif
 
+#define RXDESC_PER_CACHELINE (ARCH_DMA_MINALIGN/sizeof(struct fec_bd))
+
+/* Check various alignment issues at compile time */
+#if ((ARCH_DMA_MINALIGN < 16) || (ARCH_DMA_MINALIGN % 16 != 0))
+#error "ARCH_DMA_MINALIGN must be multiple of 16!"
+#endif
+
+#if ((PKTALIGN < ARCH_DMA_MINALIGN) || \
+	(PKTALIGN % ARCH_DMA_MINALIGN != 0))
+#error "PKTALIGN must be multiple of ARCH_DMA_MINALIGN!"
+#endif
+
 #undef DEBUG
 
 struct nbuf {
@@ -259,43 +271,52 @@ static int fec_tx_task_disable(struct fec_priv *fec)
  * Initialize receive task's buffer descriptors
  * @param[in] fec all we know about the device yet
  * @param[in] count receive buffer count to be allocated
- * @param[in] size size of each receive buffer
+ * @param[in] dsize desired size of each receive buffer
  * @return 0 on success
  *
  * For this task we need additional memory for the data buffers. And each
  * data buffer requires some alignment. Thy must be aligned to a specific
- * boundary each (DB_DATA_ALIGNMENT).
+ * boundary each.
  */
-static int fec_rbd_init(struct fec_priv *fec, int count, int size)
+static int fec_rbd_init(struct fec_priv *fec, int count, int dsize)
 {
-	int ix;
+	uint32_t size;
-	uint32_t p = 0;
+	int i;
 
-	/* reserve data memory and consider alignment */
-	if (fec->rdb_ptr == NULL)
-		fec->rdb_ptr = malloc(size * count + DB_DATA_ALIGNMENT);
-	p = (uint32_t)fec->rdb_ptr;
-	if (!p) {
-		puts("fec_mxc: not enough malloc memory\n");
-		return -ENOMEM;
-	}
-	memset((void *)p, 0, size * count + DB_DATA_ALIGNMENT);
-	p += DB_DATA_ALIGNMENT-1;
-	p &= ~(DB_DATA_ALIGNMENT-1);
-
-	for (ix = 0; ix < count; ix++) {
-		writel(p, &fec->rbd_base[ix].data_pointer);
-		p += size;
-		writew(FEC_RBD_EMPTY, &fec->rbd_base[ix].status);
-		writew(0, &fec->rbd_base[ix].data_length);
-	}
 	/*
-	 * mark the last RBD to close the ring
+	 * Allocate memory for the buffers. This allocation respects the
+	 * alignment
 	 */
-	writew(FEC_RBD_WRAP | FEC_RBD_EMPTY, &fec->rbd_base[ix - 1].status);
+	size = roundup(dsize, ARCH_DMA_MINALIGN);
+	for (i = 0; i < count; i++) {
+		uint32_t data_ptr = readl(&fec->rbd_base[i].data_pointer);
+		if (data_ptr == 0) {
+			uint8_t *data = memalign(ARCH_DMA_MINALIGN,
+						 size);
+			if (!data) {
+				printf("%s: error allocating rxbuf %d\n",
+				       __func__, i);
+				goto err;
+			}
+			writel((uint32_t)data, &fec->rbd_base[i].data_pointer);
+		} /* needs allocation */
+		writew(FEC_RBD_EMPTY, &fec->rbd_base[i].status);
+		writew(0, &fec->rbd_base[i].data_length);
+	}
+
+	/* Mark the last RBD to close the ring. */
+	writew(FEC_RBD_WRAP | FEC_RBD_EMPTY, &fec->rbd_base[i - 1].status);
 	fec->rbd_index = 0;
 
 	return 0;
+
+err:
+	for (; i >= 0; i--) {
+		uint32_t data_ptr = readl(&fec->rbd_base[i].data_pointer);
+		free((void *)data_ptr);
+	}
+
+	return -ENOMEM;
 }
 
 /**
@@ -312,9 +333,13 @@ static int fec_rbd_init(struct fec_priv *fec, int count, int size)
  */
 static void fec_tbd_init(struct fec_priv *fec)
 {
+	unsigned addr = (unsigned)fec->tbd_base;
+	unsigned size = roundup(2 * sizeof(struct fec_bd),
+				ARCH_DMA_MINALIGN);
 	writew(0x0000, &fec->tbd_base[0].status);
 	writew(FEC_TBD_WRAP, &fec->tbd_base[1].status);
 	fec->tbd_index = 0;
+	flush_dcache_range(addr, addr+size);
 }
 
 /**
@@ -324,16 +349,10 @@ static void fec_tbd_init(struct fec_priv *fec)
  */
 static void fec_rbd_clean(int last, struct fec_bd *pRbd)
 {
-	/*
+	unsigned short flags = FEC_RBD_EMPTY;
-	 * Reset buffer descriptor as empty
-	 */
 	if (last)
-		writew(FEC_RBD_WRAP | FEC_RBD_EMPTY, &pRbd->status);
+		flags |= FEC_RBD_WRAP;
-	else
+	writew(flags, &pRbd->status);
-		writew(FEC_RBD_EMPTY, &pRbd->status);
-	/*
-	 * no data in it
-	 */
 	writew(0, &pRbd->data_length);
 }
 
@@ -387,12 +406,25 @@ static int fec_open(struct eth_device *edev)
 {
 	struct fec_priv *fec = (struct fec_priv *)edev->priv;
 	int speed;
+	uint32_t addr, size;
+	int i;
 
 	debug("fec_open: fec_open(dev)\n");
 	/* full-duplex, heartbeat disabled */
 	writel(1 << 2, &fec->eth->x_cntrl);
 	fec->rbd_index = 0;
 
+	/* Invalidate all descriptors */
+	for (i = 0; i < FEC_RBD_NUM - 1; i++)
+		fec_rbd_clean(0, &fec->rbd_base[i]);
+	fec_rbd_clean(1, &fec->rbd_base[i]);
+
+	/* Flush the descriptors into RAM */
+	size = roundup(FEC_RBD_NUM * sizeof(struct fec_bd),
+			ARCH_DMA_MINALIGN);
+	addr = (uint32_t)fec->rbd_base;
+	flush_dcache_range(addr, addr + size);
+
 #ifdef FEC_QUIRK_ENET_MAC
 	/* Enable ENET HW endian SWAP */
 	writel(readl(&fec->eth->ecntrl) | FEC_ECNTRL_DBSWAP,
@@ -478,38 +510,55 @@ static int fec_open(struct eth_device *edev)
 
 static int fec_init(struct eth_device *dev, bd_t* bd)
 {
-	uint32_t base;
 	struct fec_priv *fec = (struct fec_priv *)dev->priv;
 	uint32_t mib_ptr = (uint32_t)&fec->eth->rmon_t_drop;
 	uint32_t rcntrl;
-	int i;
+	uint32_t size;
+	int i, ret;
 
 	/* Initialize MAC address */
 	fec_set_hwaddr(dev);
 
 	/*
-	 * reserve memory for both buffer descriptor chains at once
+	 * Allocate transmit descriptors, there are two in total. This
-	 * Datasheet forces the startaddress of each chain is 16 byte
+	 * allocation respects cache alignment.
-	 * aligned
 	 */
-	if (fec->base_ptr == NULL)
+	if (!fec->tbd_base) {
-		fec->base_ptr = malloc((2 + FEC_RBD_NUM) *
+		size = roundup(2 * sizeof(struct fec_bd),
-				sizeof(struct fec_bd) + DB_ALIGNMENT);
+				ARCH_DMA_MINALIGN);
-	base = (uint32_t)fec->base_ptr;
+		fec->tbd_base = memalign(ARCH_DMA_MINALIGN, size);
-	if (!base) {
+		if (!fec->tbd_base) {
-		puts("fec_mxc: not enough malloc memory\n");
+			ret = -ENOMEM;
-		return -ENOMEM;
+			goto err1;
+		}
+		memset(fec->tbd_base, 0, size);
+		fec_tbd_init(fec);
+		flush_dcache_range((unsigned)fec->tbd_base, size);
 	}
-	memset((void *)base, 0, (2 + FEC_RBD_NUM) *
-			sizeof(struct fec_bd) + DB_ALIGNMENT);
-	base += (DB_ALIGNMENT-1);
-	base &= ~(DB_ALIGNMENT-1);
 
-	fec->rbd_base = (struct fec_bd *)base;
+	/*
-
+	 * Allocate receive descriptors. This allocation respects cache
-	base += FEC_RBD_NUM * sizeof(struct fec_bd);
+	 * alignment.
-
+	 */
-	fec->tbd_base = (struct fec_bd *)base;
+	if (!fec->rbd_base) {
+		size = roundup(FEC_RBD_NUM * sizeof(struct fec_bd),
+				ARCH_DMA_MINALIGN);
+		fec->rbd_base = memalign(ARCH_DMA_MINALIGN, size);
+		if (!fec->rbd_base) {
+			ret = -ENOMEM;
+			goto err2;
+		}
+		memset(fec->rbd_base, 0, size);
+		/*
+		 * Initialize RxBD ring
+		 */
+		if (fec_rbd_init(fec, FEC_RBD_NUM, FEC_MAX_PKT_SIZE) < 0) {
+			ret = -ENOMEM;
+			goto err3;
+		}
+		flush_dcache_range((unsigned)fec->rbd_base,
+				   (unsigned)fec->rbd_base + size);
+	}
 
 	/*
 	 * Set interrupt mask register
@@ -566,23 +615,19 @@ static int fec_init(struct eth_device *dev, bd_t* bd)
 	writel((uint32_t)fec->tbd_base, &fec->eth->etdsr);
 	writel((uint32_t)fec->rbd_base, &fec->eth->erdsr);
 
-	/*
-	 * Initialize RxBD/TxBD rings
-	 */
-	if (fec_rbd_init(fec, FEC_RBD_NUM, FEC_MAX_PKT_SIZE) < 0) {
-		free(fec->base_ptr);
-		fec->base_ptr = NULL;
-		return -ENOMEM;
-	}
-	fec_tbd_init(fec);
-
-
 #ifndef CONFIG_PHYLIB
 	if (fec->xcv_type != SEVENWIRE)
 		miiphy_restart_aneg(dev);
 #endif
 	fec_open(dev);
 	return 0;
+
+err3:
+	free(fec->rbd_base);
+err2:
+	free(fec->tbd_base);
+err1:
+	return ret;
 }
 
 /**
@@ -631,9 +676,11 @@ static void fec_halt(struct eth_device *dev)
  * @param[in] length Data count in bytes
  * @return 0 on success
  */
-static int fec_send(struct eth_device *dev, volatile void* packet, int length)
+static int fec_send(struct eth_device *dev, volatile void *packet, int length)
 {
 	unsigned int status;
+	uint32_t size;
+	uint32_t addr;
 
 	/*
 	 * This routine transmits one frame.  This routine only accepts
@@ -650,15 +697,21 @@ static int fec_send(struct eth_device *dev, volatile void* packet, int length)
 	}
 
 	/*
-	 * Setup the transmit buffer
+	 * Setup the transmit buffer. We are always using the first buffer for
-	 * Note: We are always using the first buffer for transmission,
+	 * transmission, the second will be empty and only used to stop the DMA
-	 * the second will be empty and only used to stop the DMA engine
+	 * engine. We also flush the packet to RAM here to avoid cache trouble.
 	 */
 #ifdef CONFIG_FEC_MXC_SWAP_PACKET
 	swap_packet((uint32_t *)packet, length);
 #endif
+
+	addr = (uint32_t)packet;
+	size = roundup(length, ARCH_DMA_MINALIGN);
+	flush_dcache_range(addr, addr + size);
+
 	writew(length, &fec->tbd_base[fec->tbd_index].data_length);
-	writel((uint32_t)packet, &fec->tbd_base[fec->tbd_index].data_pointer);
+	writel(addr, &fec->tbd_base[fec->tbd_index].data_pointer);
+
 	/*
 	 * update BD's status now
 	 * This block:
@@ -671,17 +724,31 @@ static int fec_send(struct eth_device *dev, volatile void* packet, int length)
 	status |= FEC_TBD_LAST | FEC_TBD_TC | FEC_TBD_READY;
 	writew(status, &fec->tbd_base[fec->tbd_index].status);
 
+	/*
+	 * Flush data cache. This code flushes both TX descriptors to RAM.
+	 * After this code, the descriptors will be safely in RAM and we
+	 * can start DMA.
+	 */
+	size = roundup(2 * sizeof(struct fec_bd), ARCH_DMA_MINALIGN);
+	addr = (uint32_t)fec->tbd_base;
+	flush_dcache_range(addr, addr + size);
+
 	/*
 	 * Enable SmartDMA transmit task
 	 */
 	fec_tx_task_enable(fec);
 
 	/*
-	 * wait until frame is sent .
+	 * Wait until frame is sent. On each turn of the wait cycle, we must
+	 * invalidate data cache to see what's really in RAM. Also, we need
+	 * barrier here.
 	 */
+	invalidate_dcache_range(addr, addr + size);
 	while (readw(&fec->tbd_base[fec->tbd_index].status) & FEC_TBD_READY) {
 		udelay(1);
+		invalidate_dcache_range(addr, addr + size);
 	}
+
 	debug("fec_send: status 0x%x index %d\n",
 			readw(&fec->tbd_base[fec->tbd_index].status),
 			fec->tbd_index);
@@ -707,6 +774,8 @@ static int fec_recv(struct eth_device *dev)
 	int frame_length, len = 0;
 	struct nbuf *frame;
 	uint16_t bd_status;
+	uint32_t addr, size;
+	int i;
 	uchar buff[FEC_MAX_PKT_SIZE];
 
 	/*
@@ -737,8 +806,23 @@ static int fec_recv(struct eth_device *dev)
 	}
 
 	/*
-	 * ensure reading the right buffer status
+	 * Read the buffer status. Before the status can be read, the data cache
+	 * must be invalidated, because the data in RAM might have been changed
+	 * by DMA. The descriptors are properly aligned to cachelines so there's
+	 * no need to worry they'd overlap.
+	 *
+	 * WARNING: By invalidating the descriptor here, we also invalidate
+	 * the descriptors surrounding this one. Therefore we can NOT change the
+	 * contents of this descriptor nor the surrounding ones. The problem is
+	 * that in order to mark the descriptor as processed, we need to change
+	 * the descriptor. The solution is to mark the whole cache line when all
+	 * descriptors in the cache line are processed.
 	 */
+	addr = (uint32_t)rbd;
+	addr &= ~(ARCH_DMA_MINALIGN - 1);
+	size = roundup(sizeof(struct fec_bd), ARCH_DMA_MINALIGN);
+	invalidate_dcache_range(addr, addr + size);
+
 	bd_status = readw(&rbd->status);
 	debug("fec_recv: status 0x%x\n", bd_status);
 
@@ -750,6 +834,13 @@ static int fec_recv(struct eth_device *dev)
 			 */
 			frame = (struct nbuf *)readl(&rbd->data_pointer);
 			frame_length = readw(&rbd->data_length) - 4;
+			/*
+			 * Invalidate data cache over the buffer
+			 */
+			addr = (uint32_t)frame;
+			size = roundup(frame_length, ARCH_DMA_MINALIGN);
+			invalidate_dcache_range(addr, addr + size);
+
 			/*
 			 *  Fill the buffer and pass it to upper layers
 			 */
@@ -765,11 +856,25 @@ static int fec_recv(struct eth_device *dev)
 						(ulong)rbd->data_pointer,
 						bd_status);
 		}
+
 		/*
-		 * free the current buffer, restart the engine
+		 * Free the current buffer, restart the engine and move forward
-		 * and move forward to the next buffer
+		 * to the next buffer. Here we check if the whole cacheline of
+		 * descriptors was already processed and if so, we mark it free
+		 * as whole.
 		 */
-		fec_rbd_clean(fec->rbd_index == (FEC_RBD_NUM - 1) ? 1 : 0, rbd);
+		size = RXDESC_PER_CACHELINE - 1;
+		if ((fec->rbd_index & size) == size) {
+			i = fec->rbd_index - size;
+			addr = (uint32_t)&fec->rbd_base[i];
+			for (; i <= fec->rbd_index ; i++) {
+				fec_rbd_clean(i == (FEC_RBD_NUM - 1),
+					      &fec->rbd_base[i]);
+			}
+			flush_dcache_range(addr,
+				addr + ARCH_DMA_MINALIGN);
+		}
+
 		fec_rx_task_enable(fec);
 		fec->rbd_index = (fec->rbd_index + 1) % FEC_RBD_NUM;
 	}

drivers/net/fec_mxc.h

@@ -233,22 +233,6 @@ struct ethernet_regs {
 #define MIIGSK_ENR_EN			(1 << 1)
 #endif
 
-/**
- * @brief Descriptor buffer alignment
- *
- * i.MX27 requires a 16 byte alignment (but for the first element only)
- */
-#define DB_ALIGNMENT		16
-
-/**
- * @brief Data buffer alignment
- *
- * i.MX27 requires a four byte alignment for transmit and 16 bits
- * alignment for receive so take 16
- * Note: Valid for member data_pointer in struct buffer_descriptor
- */
-#define DB_DATA_ALIGNMENT	16
-
 /**
  * @brief Receive & Transmit Buffer Descriptor definitions
  *
@@ -282,8 +266,7 @@ struct fec_priv {
 	struct fec_bd *tbd_base;	/* TBD ring */
 	int tbd_index;			/* next transmit BD to write */
 	bd_t *bd;
-	void *rdb_ptr;
+	uint8_t *tdb_ptr;
-	void *base_ptr;
 	int dev_id;
 	int phy_id;
 	struct mii_dev *bus;