linux-kernel - [PATCH 1/3] spi: spi-xilinx: Remove ISR race condition

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Date:	Tue,  4 Jun 2013 16:02:34 +0200
From:	Michal Simek <michal.simek@...inx.com>
To:	linux-kernel@...r.kernel.org
Cc:	Michal Simek <monstr@...str.eu>,
	Michal Simek <michal.simek@...inx.com>,
	Peter Crosthwaite <pcrost@...inx.com>,
	Peter Crosthwaite <peter.crosthwaite@...alogix.com>,
	Mark Brown <broonie@...nel.org>,
	Grant Likely <grant.likely@...aro.org>,
	spi-devel-general@...ts.sourceforge.net
Subject: [PATCH 1/3] spi: spi-xilinx: Remove ISR race condition

From: Peter Crosthwaite <peter.crosthwaite@...alogix.com>

The ISR currently consumes the rx buffer data and re-enables transmission
from within interrupt context. This is bad because if the interrupt
occurs again before the ISR exits, the new interrupt will be erroneously
cleared by the still completing ISR.

Simplified the ISR by just setting the completion variable and exiting with
no action. Then just looped the transmit functionality in
xilinx_spi_txrx_bufs().

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@...inx.com>
Signed-off-by: Michal Simek <michal.simek@...inx.com>
---
 drivers/spi/spi-xilinx.c | 74 +++++++++++++++++++++++-------------------------
 1 file changed, 35 insertions(+), 39 deletions(-)

diff --git a/drivers/spi/spi-xilinx.c b/drivers/spi/spi-xilinx.c
index e1d7696..34d18dc 100644
--- a/drivers/spi/spi-xilinx.c
+++ b/drivers/spi/spi-xilinx.c
@@ -267,7 +267,6 @@ static int xilinx_spi_txrx_bufs(struct spi_device *spi, struct spi_transfer *t)
 {
 	struct xilinx_spi *xspi = spi_master_get_devdata(spi->master);
 	u32 ipif_ier;
-	u16 cr;

 	/* We get here with transmitter inhibited */

@@ -276,7 +275,6 @@ static int xilinx_spi_txrx_bufs(struct spi_device *spi, struct spi_transfer *t)
 	xspi->remaining_bytes = t->len;
 	INIT_COMPLETION(xspi->done);

-	xilinx_spi_fill_tx_fifo(xspi);

 	/* Enable the transmit empty interrupt, which we use to determine
 	 * progress on the transmission.
@@ -285,12 +283,41 @@ static int xilinx_spi_txrx_bufs(struct spi_device *spi, struct spi_transfer *t)
 	xspi->write_fn(ipif_ier | XSPI_INTR_TX_EMPTY,
 		xspi->regs + XIPIF_V123B_IIER_OFFSET);

-	/* Start the transfer by not inhibiting the transmitter any longer */
-	cr = xspi->read_fn(xspi->regs + XSPI_CR_OFFSET) &
-		~XSPI_CR_TRANS_INHIBIT;
-	xspi->write_fn(cr, xspi->regs + XSPI_CR_OFFSET);
+	for (;;) {
+		u16 cr;
+		u8 sr;
+
+		xilinx_spi_fill_tx_fifo(xspi);
+
+		/* Start the transfer by not inhibiting the transmitter any
+		 * longer
+		 */
+		cr = xspi->read_fn(xspi->regs + XSPI_CR_OFFSET) &
+							~XSPI_CR_TRANS_INHIBIT;
+		xspi->write_fn(cr, xspi->regs + XSPI_CR_OFFSET);
+
+		wait_for_completion(&xspi->done);
+
+		/* A transmit has just completed. Process received data and
+		 * check for more data to transmit. Always inhibit the
+		 * transmitter while the Isr refills the transmit register/FIFO,
+		 * or make sure it is stopped if we're done.
+		 */
+		cr = xspi->read_fn(xspi->regs + XSPI_CR_OFFSET);
+		xspi->write_fn(cr | XSPI_CR_TRANS_INHIBIT,
+			       xspi->regs + XSPI_CR_OFFSET);
+
+		/* Read out all the data from the Rx FIFO */
+		sr = xspi->read_fn(xspi->regs + XSPI_SR_OFFSET);
+		while ((sr & XSPI_SR_RX_EMPTY_MASK) == 0) {
+			xspi->rx_fn(xspi);
+			sr = xspi->read_fn(xspi->regs + XSPI_SR_OFFSET);
+		}

-	wait_for_completion(&xspi->done);
+		/* See if there is more data to send */
+		if (!xspi->remaining_bytes > 0)
+			break;
+	}

 	/* Disable the transmit empty interrupt */
 	xspi->write_fn(ipif_ier, xspi->regs + XIPIF_V123B_IIER_OFFSET);
@@ -314,38 +341,7 @@ static irqreturn_t xilinx_spi_irq(int irq, void *dev_id)
 	xspi->write_fn(ipif_isr, xspi->regs + XIPIF_V123B_IISR_OFFSET);

 	if (ipif_isr & XSPI_INTR_TX_EMPTY) {	/* Transmission completed */
-		u16 cr;
-		u8 sr;
-
-		/* A transmit has just completed. Process received data and
-		 * check for more data to transmit. Always inhibit the
-		 * transmitter while the Isr refills the transmit register/FIFO,
-		 * or make sure it is stopped if we're done.
-		 */
-		cr = xspi->read_fn(xspi->regs + XSPI_CR_OFFSET);
-		xspi->write_fn(cr | XSPI_CR_TRANS_INHIBIT,
-			xspi->regs + XSPI_CR_OFFSET);
-
-		/* Read out all the data from the Rx FIFO */
-		sr = xspi->read_fn(xspi->regs + XSPI_SR_OFFSET);
-		while ((sr & XSPI_SR_RX_EMPTY_MASK) == 0) {
-			xspi->rx_fn(xspi);
-			sr = xspi->read_fn(xspi->regs + XSPI_SR_OFFSET);
-		}
-
-		/* See if there is more data to send */
-		if (xspi->remaining_bytes > 0) {
-			xilinx_spi_fill_tx_fifo(xspi);
-			/* Start the transfer by not inhibiting the
-			 * transmitter any longer
-			 */
-			xspi->write_fn(cr, xspi->regs + XSPI_CR_OFFSET);
-		} else {
-			/* No more data to send.
-			 * Indicate the transfer is completed.
-			 */
-			complete(&xspi->done);
-		}
+		complete(&xspi->done);
 	}

 	return IRQ_HANDLED;
--
1.8.2.3


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