[PATCH 2/2] spi: sh-msiof: Fix leaking of unused DMA descriptors

[Geert Uytterhoeven <geert+renesas@xxxxxxxxx>]

If dmaengine_prep_slave_sg() or dmaengine_submit() fail, we may leak
unused DMA descriptors.

As per Documentation/dmaengine.txt, once a DMA descriptor has been
obtained, it must be submitted. Hence:
  - First prepare and submit all DMA descriptors,
  - Prepare the SPI controller for DMA,
  - Start DMA by calling dma_async_issue_pending(),
  - Make sure to call dmaengine_terminate_all() on all descriptors that
    haven't completed.

Reported-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx>
---
 drivers/spi/spi-sh-msiof.c | 71 +++++++++++++++++++++++++---------------------
 1 file changed, 38 insertions(+), 33 deletions(-)

diff --git a/drivers/spi/spi-sh-msiof.c b/drivers/spi/spi-sh-msiof.c
index 2a4354dcd661..887c2084130f 100644
--- a/drivers/spi/spi-sh-msiof.c
+++ b/drivers/spi/spi-sh-msiof.c
@@ -636,48 +636,38 @@ static int sh_msiof_dma_once(struct sh_msiof_spi_priv *p, const void *tx,
 	dma_cookie_t cookie;
 	int ret;
 
-	if (tx) {
-		ier_bits |= IER_TDREQE | IER_TDMAE;
-		dma_sync_single_for_device(p->master->dma_tx->device->dev,
-					   p->tx_dma_addr, len, DMA_TO_DEVICE);
-		desc_tx = dmaengine_prep_slave_single(p->master->dma_tx,
-					p->tx_dma_addr, len, DMA_TO_DEVICE,
-					DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
-		if (!desc_tx)
-			return -EAGAIN;
-	}
-
+	/* First prepare and submit the DMA request(s), as this may fail */
 	if (rx) {
 		ier_bits |= IER_RDREQE | IER_RDMAE;
 		desc_rx = dmaengine_prep_slave_single(p->master->dma_rx,
 					p->rx_dma_addr, len, DMA_FROM_DEVICE,
 					DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
-		if (!desc_rx)
-			return -EAGAIN;
-	}
-
-	/* 1 stage FIFO watermarks for DMA */
-	sh_msiof_write(p, FCTR, FCTR_TFWM_1 | FCTR_RFWM_1);
-
-	/* setup msiof transfer mode registers (32-bit words) */
-	sh_msiof_spi_set_mode_regs(p, tx, rx, 32, len / 4);
-
-	sh_msiof_write(p, IER, ier_bits);
-
-	reinit_completion(&p->done);
+		if (!desc_rx) {
+			ret = -EAGAIN;
+			goto no_dma_rx;
+		}
 
-	if (rx) {
 		desc_rx->callback = sh_msiof_dma_complete;
 		desc_rx->callback_param = p;
 		cookie = dmaengine_submit(desc_rx);
 		if (dma_submit_error(cookie)) {
 			ret = cookie;
-			goto stop_ier;
+			goto no_dma_rx;
 		}
-		dma_async_issue_pending(p->master->dma_rx);
 	}
 
 	if (tx) {
+		ier_bits |= IER_TDREQE | IER_TDMAE;
+		dma_sync_single_for_device(p->master->dma_tx->device->dev,
+					   p->tx_dma_addr, len, DMA_TO_DEVICE);
+		desc_tx = dmaengine_prep_slave_single(p->master->dma_tx,
+					p->tx_dma_addr, len, DMA_TO_DEVICE,
+					DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
+		if (!desc_tx) {
+			ret = -EAGAIN;
+			goto no_dma_tx;
+		}
+
 		if (rx) {
 			/* No callback */
 			desc_tx->callback = NULL;
@@ -688,15 +678,30 @@ static int sh_msiof_dma_once(struct sh_msiof_spi_priv *p, const void *tx,
 		cookie = dmaengine_submit(desc_tx);
 		if (dma_submit_error(cookie)) {
 			ret = cookie;
-			goto stop_rx;
+			goto no_dma_tx;
 		}
-		dma_async_issue_pending(p->master->dma_tx);
 	}
 
+	/* 1 stage FIFO watermarks for DMA */
+	sh_msiof_write(p, FCTR, FCTR_TFWM_1 | FCTR_RFWM_1);
+
+	/* setup msiof transfer mode registers (32-bit words) */
+	sh_msiof_spi_set_mode_regs(p, tx, rx, 32, len / 4);
+
+	sh_msiof_write(p, IER, ier_bits);
+
+	reinit_completion(&p->done);
+
+	/* Now start DMA */
+	if (tx)
+		dma_async_issue_pending(p->master->dma_rx);
+	if (rx)
+		dma_async_issue_pending(p->master->dma_tx);
+
 	ret = sh_msiof_spi_start(p, rx);
 	if (ret) {
 		dev_err(&p->pdev->dev, "failed to start hardware\n");
-		goto stop_tx;
+		goto stop_dma;
 	}
 
 	/* wait for tx fifo to be emptied / rx fifo to be filled */
@@ -726,14 +731,14 @@ static int sh_msiof_dma_once(struct sh_msiof_spi_priv *p, const void *tx,
 stop_reset:
 	sh_msiof_reset_str(p);
 	sh_msiof_spi_stop(p, rx);
-stop_tx:
+stop_dma:
 	if (tx)
 		dmaengine_terminate_all(p->master->dma_tx);
-stop_rx:
+no_dma_tx:
 	if (rx)
 		dmaengine_terminate_all(p->master->dma_rx);
-stop_ier:
 	sh_msiof_write(p, IER, 0);
+no_dma_rx:
 	return ret;
 }
 
-- 
1.9.1

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