[PATCH 08/13] powerpc/5200: LocalPlus driver: smart flush of receive FIFO

[Roman Fietze]

Signed-off-by: Roman Fietze <roman.fietze at telemotive.de>
---
 arch/powerpc/platforms/52xx/mpc52xx_lpbfifo.c |   40 ++++++++++++++++---------
 1 files changed, 26 insertions(+), 14 deletions(-)

diff --git a/arch/powerpc/platforms/52xx/mpc52xx_lpbfifo.c b/arch/powerpc/platforms/52xx/mpc52xx_lpbfifo.c
index a7cd585..48f2b4f 100644
--- a/arch/powerpc/platforms/52xx/mpc52xx_lpbfifo.c
+++ b/arch/powerpc/platforms/52xx/mpc52xx_lpbfifo.c
@@ -84,8 +84,7 @@ static void mpc52xx_lpbfifo_kick(struct mpc52xx_lpbfifo_request *req)
 	struct bcom_bd *bd;
 	void __iomem *reg;
 	u32 *data;
-	int i;
-	int bit_fields;
+	u32 bit_fields;
 	int rflags = req->flags;
 
 	/* Set and clear the reset bits; is good practice in User Manual */
@@ -96,27 +95,32 @@ static void mpc52xx_lpbfifo_kick(struct mpc52xx_lpbfifo_request *req)
 
 	/* Set CS and BPT */
 	bit_fields = MPC52xx_SCLPC_CONTROL_CS(req->cs) | 0x8;
-	if (!(mpc52xx_lpbfifo_is_write(rflags))) {
+	if (!(mpc52xx_lpbfifo_is_write(rflags)))
 		bit_fields |= MPC52xx_SCLPC_CONTROL_RWB_RECEIVE;	/* read mode */
-		bit_fields |= MPC52xx_SCLPC_CONTROL_FLUSH;
-	}
-	out_be32(&lpbfifo.regs->control, bit_fields);
 
 	if (!mpc52xx_lpbfifo_is_dma(rflags)) {
-		/* While the FIFO can be setup for transfer sizes as large as
-		 * 16M-1, the FIFO itself is only 512 bytes deep and it does
-		 * not generate interrupts for FIFO full events (only transfer
-		 * complete will raise an IRQ).  Therefore when not using
-		 * Bestcomm to drive the FIFO it needs to either be polled, or
-		 * transfers need to constrained to the size of the fifo.
+		/* While the FIFO can be setup for transfer sizes as
+		 * large as 16M-1, the FIFO itself is only 512 bytes
+		 * deep and it does not generate interrupts for FIFO
+		 * full events (only transfer complete will raise an
+		 * IRQ). Therefore when not using Bestcomm to drive the
+		 * FIFO it needs to either be polled, or transfers need
+		 * to constrained to the size of the fifo.
 		 *
 		 * This driver restricts the size of the transfer
+		 *
+		 * The last block of data will be received with the
+		 * flush bit set. This avoids stale read data.
 		 */
 		if (transfer_size > 512)
 			transfer_size = 512;
+		else if (!(mpc52xx_lpbfifo_is_write(rflags)))
+			bit_fields |= MPC52xx_SCLPC_CONTROL_FLUSH;
 
 		/* Load the FIFO with data */
 		if (mpc52xx_lpbfifo_is_write(rflags)) {
+			size_t i;
+
 			reg = &lpbfifo.regs->fifo_data;
 			data = req->data + req->pos;
 			for (i = 0; i < transfer_size; i += 4)
@@ -128,6 +132,12 @@ static void mpc52xx_lpbfifo_kick(struct mpc52xx_lpbfifo_request *req)
 						 MPC52xx_SCLPC_ENABLE_NIE |
 						 MPC52xx_SCLPC_ENABLE_ME));
 	} else {
+
+		/* In DMA mode we can always set the flush bit to avoid
+		 * stale read data. */
+		if (!(mpc52xx_lpbfifo_is_write(rflags)))
+			bit_fields |= MPC52xx_SCLPC_CONTROL_FLUSH;
+
 		/* Choose the correct direction
 		 *
 		 * Configure the watermarks so DMA will always complete correctly.
@@ -168,6 +178,8 @@ static void mpc52xx_lpbfifo_kick(struct mpc52xx_lpbfifo_request *req)
 		bcom_submit_next_buffer(lpbfifo.bcom_cur_task, NULL);
 	}
 
+	out_be32(&lpbfifo.regs->control, bit_fields);
+
 	/* Set packet size and kick it off */
 	out_be32(&lpbfifo.regs->packet_size.packet_size, MPC52xx_SCLPC_PACKET_SIZE_RESTART | transfer_size);
 	if (mpc52xx_lpbfifo_is_dma(rflags))
@@ -455,7 +467,7 @@ mpc52xx_lpbfifo_probe(struct of_device *op, const struct of_device_id *match)
 		goto err_irq;
 
 	/* Request the Bestcomm receive (fifo --> memory) task and IRQ */
-	lpbfifo.bcom_rx_task = bcom_gen_bd_rx_init(4,
+	lpbfifo.bcom_rx_task = bcom_gen_bd_rx_init(2,
 						   res.start + offsetof(struct mpc52xx_sclpc, fifo_data),
 						   BCOM_INITIATOR_SCLPC, BCOM_IPR_SCLPC,
 						   16 * 1024 * 1024);
@@ -469,7 +481,7 @@ mpc52xx_lpbfifo_probe(struct of_device *op, const struct of_device_id *match)
 		goto err_bcom_rx_irq;
 
 	/* Request the Bestcomm transmit (memory --> fifo) task and IRQ */
-	lpbfifo.bcom_tx_task = bcom_gen_bd_tx_init(4,
+	lpbfifo.bcom_tx_task = bcom_gen_bd_tx_init(2,
 						   res.start + offsetof(struct mpc52xx_sclpc, fifo_data),
 						   BCOM_INITIATOR_SCLPC,
 						   BCOM_IPR_SCLPC);
-- 
1.6.5.5



-- 
Roman Fietze                Telemotive AG Büro Mühlhausen
Breitwiesen                              73347 Mühlhausen
Tel.: +49(0)7335/18493-45        http://www.telemotive.de