Merge branch 'Scatter-gather-SPI-for-SJA1105-DSA'

Vladimir Oltean says:

====================
Scatter/gather SPI for SJA1105 DSA

This is a small series that reduces the stack memory usage for the
sja1105 driver.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/dsa/sja1105/sja1105.h

@@ -121,7 +121,7 @@ int sja1105_static_config_reload(struct sja1105_private *priv);
 /* From sja1105_spi.c */
 int sja1105_xfer_buf(const struct sja1105_private *priv,
 		     sja1105_spi_rw_mode_t rw, u64 reg_addr,
-		     void *packed_buf, size_t size_bytes);
+		     u8 *buf, size_t len);
 int sja1105_xfer_u32(const struct sja1105_private *priv,
 		     sja1105_spi_rw_mode_t rw, u64 reg_addr, u32 *value);
 int sja1105_xfer_u64(const struct sja1105_private *priv,

drivers/net/dsa/sja1105/sja1105_spi.c

@@ -10,38 +10,12 @@
 #define SJA1105_SIZE_RESET_CMD		4
 #define SJA1105_SIZE_SPI_MSG_HEADER	4
 #define SJA1105_SIZE_SPI_MSG_MAXLEN	(64 * 4)
-#define SJA1105_SIZE_SPI_TRANSFER_MAX	\
-	(SJA1105_SIZE_SPI_MSG_HEADER + SJA1105_SIZE_SPI_MSG_MAXLEN)
 
-static int sja1105_spi_transfer(const struct sja1105_private *priv,
-				const void *tx, void *rx, int size)
-{
-	struct spi_device *spi = priv->spidev;
-	struct spi_transfer transfer = {
-		.tx_buf = tx,
-		.rx_buf = rx,
-		.len = size,
-	};
-	struct spi_message msg;
-	int rc;
-
-	if (size > SJA1105_SIZE_SPI_TRANSFER_MAX) {
-		dev_err(&spi->dev, "SPI message (%d) longer than max of %d\n",
-			size, SJA1105_SIZE_SPI_TRANSFER_MAX);
-		return -EMSGSIZE;
-	}
-
-	spi_message_init(&msg);
-	spi_message_add_tail(&transfer, &msg);
-
-	rc = spi_sync(spi, &msg);
-	if (rc < 0) {
-		dev_err(&spi->dev, "SPI transfer failed: %d\n", rc);
-		return rc;
-	}
-
-	return rc;
-}
+struct sja1105_chunk {
+	u8	*buf;
+	size_t	len;
+	u64	reg_addr;
+};
 
 static void
 sja1105_spi_message_pack(void *buf, const struct sja1105_spi_message *msg)
@@ -55,49 +29,98 @@ sja1105_spi_message_pack(void *buf, const struct sja1105_spi_message *msg)
 	sja1105_pack(buf, &msg->address,    24,  4, size);
 }
 
+#define sja1105_hdr_xfer(xfers, chunk) \
+	((xfers) + 2 * (chunk))
+#define sja1105_chunk_xfer(xfers, chunk) \
+	((xfers) + 2 * (chunk) + 1)
+#define sja1105_hdr_buf(hdr_bufs, chunk) \
+	((hdr_bufs) + (chunk) * SJA1105_SIZE_SPI_MSG_HEADER)
+
 /* If @rw is:
  * - SPI_WRITE: creates and sends an SPI write message at absolute
- *		address reg_addr, taking size_bytes from *packed_buf
+ *		address reg_addr, taking @len bytes from *buf
  * - SPI_READ:  creates and sends an SPI read message from absolute
- *		address reg_addr, writing size_bytes into *packed_buf
- *
- * This function should only be called if it is priorly known that
- * @size_bytes is smaller than SIZE_SPI_MSG_MAXLEN. Larger packed buffers
- * are chunked in smaller pieces by sja1105_xfer_long_buf below.
+ *		address reg_addr, writing @len bytes into *buf
  */
 int sja1105_xfer_buf(const struct sja1105_private *priv,
 		     sja1105_spi_rw_mode_t rw, u64 reg_addr,
-		     void *packed_buf, size_t size_bytes)
+		     u8 *buf, size_t len)
 {
-	u8 tx_buf[SJA1105_SIZE_SPI_TRANSFER_MAX] = {0};
-	u8 rx_buf[SJA1105_SIZE_SPI_TRANSFER_MAX] = {0};
-	const int msg_len = size_bytes + SJA1105_SIZE_SPI_MSG_HEADER;
-	struct sja1105_spi_message msg = {0};
-	int rc;
+	struct sja1105_chunk chunk = {
+		.len = min_t(size_t, len, SJA1105_SIZE_SPI_MSG_MAXLEN),
+		.reg_addr = reg_addr,
+		.buf = buf,
+	};
+	struct spi_device *spi = priv->spidev;
+	struct spi_transfer *xfers;
+	int num_chunks;
+	int rc, i = 0;
+	u8 *hdr_bufs;
 
-	if (msg_len > SJA1105_SIZE_SPI_TRANSFER_MAX)
-		return -ERANGE;
+	num_chunks = DIV_ROUND_UP(len, SJA1105_SIZE_SPI_MSG_MAXLEN);
 
-	msg.access = rw;
-	msg.address = reg_addr;
-	if (rw == SPI_READ)
-		msg.read_count = size_bytes / 4;
+	/* One transfer for each message header, one for each message
+	 * payload (chunk).
+	 */
+	xfers = kcalloc(2 * num_chunks, sizeof(struct spi_transfer),
+			GFP_KERNEL);
+	if (!xfers)
+		return -ENOMEM;
 
-	sja1105_spi_message_pack(tx_buf, &msg);
+	/* Packed buffers for the num_chunks SPI message headers,
+	 * stored as a contiguous array
+	 */
+	hdr_bufs = kcalloc(num_chunks, SJA1105_SIZE_SPI_MSG_HEADER,
+			   GFP_KERNEL);
+	if (!hdr_bufs) {
+		kfree(xfers);
+		return -ENOMEM;
+	}
 
-	if (rw == SPI_WRITE)
-		memcpy(tx_buf + SJA1105_SIZE_SPI_MSG_HEADER,
-		       packed_buf, size_bytes);
+	for (i = 0; i < num_chunks; i++) {
+		struct spi_transfer *chunk_xfer = sja1105_chunk_xfer(xfers, i);
+		struct spi_transfer *hdr_xfer = sja1105_hdr_xfer(xfers, i);
+		u8 *hdr_buf = sja1105_hdr_buf(hdr_bufs, i);
+		struct sja1105_spi_message msg;
+
+		/* Populate the transfer's header buffer */
+		msg.address = chunk.reg_addr;
+		msg.access = rw;
+		if (rw == SPI_READ)
+			msg.read_count = chunk.len / 4;
+		else
+			/* Ignored */
+			msg.read_count = 0;
+		sja1105_spi_message_pack(hdr_buf, &msg);
+		hdr_xfer->tx_buf = hdr_buf;
+		hdr_xfer->len = SJA1105_SIZE_SPI_MSG_HEADER;
+
+		/* Populate the transfer's data buffer */
+		if (rw == SPI_READ)
+			chunk_xfer->rx_buf = chunk.buf;
+		else
+			chunk_xfer->tx_buf = chunk.buf;
+		chunk_xfer->len = chunk.len;
+
+		/* Calculate next chunk */
+		chunk.buf += chunk.len;
+		chunk.reg_addr += chunk.len / 4;
+		chunk.len = min_t(size_t, (ptrdiff_t)(buf + len - chunk.buf),
+				  SJA1105_SIZE_SPI_MSG_MAXLEN);
+
+		/* De-assert the chip select after each chunk. */
+		if (chunk.len)
+			chunk_xfer->cs_change = 1;
+	}
 
-	rc = sja1105_spi_transfer(priv, tx_buf, rx_buf, msg_len);
+	rc = spi_sync_transfer(spi, xfers, 2 * num_chunks);
 	if (rc < 0)
-		return rc;
+		dev_err(&spi->dev, "SPI transfer failed: %d\n", rc);
 
-	if (rw == SPI_READ)
-		memcpy(packed_buf, rx_buf + SJA1105_SIZE_SPI_MSG_HEADER,
-		       size_bytes);
+	kfree(hdr_bufs);
+	kfree(xfers);
 
-	return 0;
+	return rc;
 }
 
 /* If @rw is:
@@ -152,43 +175,6 @@ int sja1105_xfer_u32(const struct sja1105_private *priv,
 	return rc;
 }
 
-/* Should be used if a @packed_buf larger than SJA1105_SIZE_SPI_MSG_MAXLEN
- * must be sent/received. Splitting the buffer into chunks and assembling
- * those into SPI messages is done automatically by this function.
- */
-static int sja1105_xfer_long_buf(const struct sja1105_private *priv,
-				 sja1105_spi_rw_mode_t rw, u64 base_addr,
-				 void *packed_buf, u64 buf_len)
-{
-	struct chunk {
-		void *buf_ptr;
-		int len;
-		u64 spi_address;
-	} chunk;
-	int distance_to_end;
-	int rc;
-
-	/* Initialize chunk */
-	chunk.buf_ptr = packed_buf;
-	chunk.spi_address = base_addr;
-	chunk.len = min_t(int, buf_len, SJA1105_SIZE_SPI_MSG_MAXLEN);
-
-	while (chunk.len) {
-		rc = sja1105_xfer_buf(priv, rw, chunk.spi_address,
-				      chunk.buf_ptr, chunk.len);
-		if (rc < 0)
-			return rc;
-
-		chunk.buf_ptr += chunk.len;
-		chunk.spi_address += chunk.len / 4;
-		distance_to_end = (uintptr_t)(packed_buf + buf_len -
-					      chunk.buf_ptr);
-		chunk.len = min(distance_to_end, SJA1105_SIZE_SPI_MSG_MAXLEN);
-	}
-
-	return 0;
-}
-
 /* Back-ported structure from UM11040 Table 112.
  * Reset control register (addr. 100440h)
  * In the SJA1105 E/T, only warm_rst and cold_rst are
@@ -451,8 +437,8 @@ int sja1105_static_config_upload(struct sja1105_private *priv)
 		/* Wait for the switch to come out of reset */
 		usleep_range(1000, 5000);
 		/* Upload the static config to the device */
-		rc = sja1105_xfer_long_buf(priv, SPI_WRITE, regs->config,
-					   config_buf, buf_len);
+		rc = sja1105_xfer_buf(priv, SPI_WRITE, regs->config,
+				      config_buf, buf_len);
 		if (rc < 0) {
 			dev_err(dev, "Failed to upload config, retrying...\n");
 			continue;