[PATCH] spi: s3c64xx: requests spi-dma channel only during data transfer

[PATCH] spi: s3c64xx: requests spi-dma channel only during data transfer

[Adithya K V]

Current s3c64xx SPI driver acquires DMA channel during driver
probe and holds on it even when channels are not used
(no DMA transfer). This is a problem especially when all the
DMA channels are exhausted (as other IPs on the same DMA
controller also acquires DMA channel) and if a new IP/Device
requests for a DMA channel (on the same DMA controller), it won’t
get DMA channel allocated.
The said issue can be avoided if s3c64xx driver request and
release DMA channel before and after data transfer. Let’s modify
the driver to request and release DMA channel before and after
DMA mode data transfer.

Signed-off-by: Adithya K V <adithya.kv@samsung.com>
---
 drivers/spi/spi-s3c64xx.c | 56 ++++++++++++++++++++++-----------------
 1 file changed, 32 insertions(+), 24 deletions(-)

diff --git a/drivers/spi/spi-s3c64xx.c b/drivers/spi/spi-s3c64xx.c
index c26440e9058d..82558e37c735 100644
--- a/drivers/spi/spi-s3c64xx.c
+++ b/drivers/spi/spi-s3c64xx.c
@@ -350,6 +350,23 @@ static int s3c64xx_spi_prepare_transfer(struct spi_master *spi)
 	if (is_polling(sdd))
 		return 0;
 
+	/* Requests DMA channels */
+	sdd->rx_dma.ch = dma_request_chan(&sdd->pdev->dev, "rx");
+	if (IS_ERR(sdd->rx_dma.ch)) {
+		dev_err(&sdd->pdev->dev, "Failed to get RX DMA channel\n");
+		sdd->rx_dma.ch = 0;
+		return 0;
+	}
+
+	sdd->tx_dma.ch = dma_request_chan(&sdd->pdev->dev, "tx");
+	if (IS_ERR(sdd->tx_dma.ch)) {
+		dev_err(&sdd->pdev->dev, "Failed to get TX DMA hannel\n");
+		dma_release_channel(sdd->rx_dma.ch);
+		sdd->tx_dma.ch = 0;
+		sdd->rx_dma.ch = 0;
+		return 0;
+	}
+
 	spi->dma_rx = sdd->rx_dma.ch;
 	spi->dma_tx = sdd->tx_dma.ch;
 
@@ -362,7 +379,12 @@ static bool s3c64xx_spi_can_dma(struct spi_master *master,
 {
 	struct s3c64xx_spi_driver_data *sdd = spi_master_get_devdata(master);
 
-	return xfer->len > (FIFO_LVL_MASK(sdd) >> 1) + 1;
+	if (sdd->rx_dma.ch && sdd->tx_dma.ch) {
+		return xfer->len > (FIFO_LVL_MASK(sdd) >> 1) + 1;
+	} else {
+		return 0;
+	}
+
 }
 
 static int s3c64xx_enable_datapath(struct s3c64xx_spi_driver_data *sdd,
@@ -697,7 +719,7 @@ static int s3c64xx_spi_transfer_one(struct spi_master *master,
 	    sdd->rx_dma.ch && sdd->tx_dma.ch) {
 		use_dma = 1;
 
-	} else if (is_polling(sdd) && xfer->len > fifo_len) {
+	} else if (xfer->len > fifo_len) {
 		tx_buf = xfer->tx_buf;
 		rx_buf = xfer->rx_buf;
 		origin_len = xfer->len;
@@ -782,6 +804,14 @@ static int s3c64xx_spi_transfer_one(struct spi_master *master,
 		xfer->len = origin_len;
 	}
 
+	/* Releases DMA channels after data transfer is completed */
+	if (sdd->rx_dma.ch && sdd->tx_dma.ch) {
+		dma_release_channel(sdd->rx_dma.ch);
+		dma_release_channel(sdd->tx_dma.ch);
+		sdd->rx_dma.ch = 0;
+		sdd->tx_dma.ch = 0;
+	}
+
 	return status;
 }
 
@@ -1167,22 +1197,6 @@ static int s3c64xx_spi_probe(struct platform_device *pdev)
 		}
 	}
 
-	if (!is_polling(sdd)) {
-		/* Acquire DMA channels */
-		sdd->rx_dma.ch = dma_request_chan(&pdev->dev, "rx");
-		if (IS_ERR(sdd->rx_dma.ch)) {
-			dev_err(&pdev->dev, "Failed to get RX DMA channel\n");
-			ret = PTR_ERR(sdd->rx_dma.ch);
-			goto err_disable_io_clk;
-		}
-		sdd->tx_dma.ch = dma_request_chan(&pdev->dev, "tx");
-		if (IS_ERR(sdd->tx_dma.ch)) {
-			dev_err(&pdev->dev, "Failed to get TX DMA channel\n");
-			ret = PTR_ERR(sdd->tx_dma.ch);
-			goto err_release_rx_dma;
-		}
-	}
-
 	pm_runtime_set_autosuspend_delay(&pdev->dev, AUTOSUSPEND_TIMEOUT);
 	pm_runtime_use_autosuspend(&pdev->dev);
 	pm_runtime_set_active(&pdev->dev);
@@ -1228,12 +1242,6 @@ static int s3c64xx_spi_probe(struct platform_device *pdev)
 	pm_runtime_disable(&pdev->dev);
 	pm_runtime_set_suspended(&pdev->dev);
 
-	if (!is_polling(sdd))
-		dma_release_channel(sdd->tx_dma.ch);
-err_release_rx_dma:
-	if (!is_polling(sdd))
-		dma_release_channel(sdd->rx_dma.ch);
-err_disable_io_clk:
 	clk_disable_unprepare(sdd->ioclk);
 err_disable_src_clk:
 	clk_disable_unprepare(sdd->src_clk);

base-commit: 09ce5091ff971cdbfd67ad84dc561ea27f10d67a
-- 
2.17.1

Re: [PATCH] spi: s3c64xx: requests spi-dma channel only during data transfer

[Mark Brown]

On Tue, 24 May 2022 19:31:32 +0530, Adithya K V wrote:
> Current s3c64xx SPI driver acquires DMA channel during driver
> probe and holds on it even when channels are not used
> (no DMA transfer). This is a problem especially when all the
> DMA channels are exhausted (as other IPs on the same DMA
> controller also acquires DMA channel) and if a new IP/Device
> requests for a DMA channel (on the same DMA controller), it won’t
> get DMA channel allocated.
> The said issue can be avoided if s3c64xx driver request and
> release DMA channel before and after data transfer. Let’s modify
> the driver to request and release DMA channel before and after
> DMA mode data transfer.
> 
> [...]

Applied to

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next

Thanks!

[1/1] spi: s3c64xx: requests spi-dma channel only during data transfer
      commit: f52b03c707444c5a3d1a0b9c5724f93ddc3c588e

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark