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From: Serge Semin <Sergey.Semin@baikalelectronics.ru>
To: Mark Brown <broonie@kernel.org>
Cc: Serge Semin <Sergey.Semin@baikalelectronics.ru>,
	Serge Semin <fancer.lancer@gmail.com>,
	Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
	Georgy Vlasov <Georgy.Vlasov@baikalelectronics.ru>,
	Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru>,
	Pavel Parkhomenko <Pavel.Parkhomenko@baikalelectronics.ru>,
	Peter Ujfalusi <peter.ujfalusi@ti.com>,
	Andy Shevchenko <andy.shevchenko@gmail.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Feng Tang <feng.tang@intel.com>, Vinod Koul <vkoul@kernel.org>,
	<linux-spi@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: [PATCH 1/8] spi: dw-dma: Set DMA Level registers on init
Date: Fri, 31 Jul 2020 10:59:46 +0300
Message-ID: <20200731075953.14416-2-Sergey.Semin@baikalelectronics.ru> (raw)
In-Reply-To: <20200731075953.14416-1-Sergey.Semin@baikalelectronics.ru>

Indeed the registers content doesn't get cleared when the SPI controller
is disabled and enabled. Max burst lengths aren't changed since the Rx and
Tx DMA channels are requested on init stage and are kept acquired until
the device is removed. Obviously SPI controller FIFO depth can't be
changed. Due to all of that we can safely move the DMA Transmit and
Receive data level registers initialization to the SPI controller DMA init
stage (when the SPI controller is being probed) instead of doing it for
each SPI transfer when dma_setup is called. This shall speed the DMA-based
SPI transfer initialization up a bit, particularly if the APB bus is
relatively slow.

Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
---
 drivers/spi/spi-dw-dma.c | 29 ++++++++++++++---------------
 1 file changed, 14 insertions(+), 15 deletions(-)

diff --git a/drivers/spi/spi-dw-dma.c b/drivers/spi/spi-dw-dma.c
index bb390ff67d1d..440679fa0764 100644
--- a/drivers/spi/spi-dw-dma.c
+++ b/drivers/spi/spi-dw-dma.c
@@ -49,6 +49,7 @@ static void dw_spi_dma_maxburst_init(struct dw_spi *dws)
 		max_burst = RX_BURST_LEVEL;
 
 	dws->rxburst = min(max_burst, def_burst);
+	dw_writel(dws, DW_SPI_DMARDLR, dws->rxburst - 1);
 
 	ret = dma_get_slave_caps(dws->txchan, &caps);
 	if (!ret && caps.max_burst)
@@ -56,7 +57,20 @@ static void dw_spi_dma_maxburst_init(struct dw_spi *dws)
 	else
 		max_burst = TX_BURST_LEVEL;
 
+	/*
+	 * Having a Rx DMA channel serviced with higher priority than a Tx DMA
+	 * channel might not be enough to provide a well balanced DMA-based
+	 * SPI transfer interface. There might still be moments when the Tx DMA
+	 * channel is occasionally handled faster than the Rx DMA channel.
+	 * That in its turn will eventually cause the SPI Rx FIFO overflow if
+	 * SPI bus speed is high enough to fill the SPI Rx FIFO in before it's
+	 * cleared by the Rx DMA channel. In order to fix the problem the Tx
+	 * DMA activity is intentionally slowed down by limiting the SPI Tx
+	 * FIFO depth with a value twice bigger than the Tx burst length
+	 * calculated earlier by the dw_spi_dma_maxburst_init() method.
+	 */
 	dws->txburst = min(max_burst, def_burst);
+	dw_writel(dws, DW_SPI_DMATDLR, dws->txburst);
 }
 
 static int dw_spi_dma_init_mfld(struct device *dev, struct dw_spi *dws)
@@ -372,21 +386,6 @@ static int dw_spi_dma_setup(struct dw_spi *dws, struct spi_transfer *xfer)
 {
 	u16 imr = 0, dma_ctrl = 0;
 
-	/*
-	 * Having a Rx DMA channel serviced with higher priority than a Tx DMA
-	 * channel might not be enough to provide a well balanced DMA-based
-	 * SPI transfer interface. There might still be moments when the Tx DMA
-	 * channel is occasionally handled faster than the Rx DMA channel.
-	 * That in its turn will eventually cause the SPI Rx FIFO overflow if
-	 * SPI bus speed is high enough to fill the SPI Rx FIFO in before it's
-	 * cleared by the Rx DMA channel. In order to fix the problem the Tx
-	 * DMA activity is intentionally slowed down by limiting the SPI Tx
-	 * FIFO depth with a value twice bigger than the Tx burst length
-	 * calculated earlier by the dw_spi_dma_maxburst_init() method.
-	 */
-	dw_writel(dws, DW_SPI_DMARDLR, dws->rxburst - 1);
-	dw_writel(dws, DW_SPI_DMATDLR, dws->txburst);
-
 	if (xfer->tx_buf)
 		dma_ctrl |= SPI_DMA_TDMAE;
 	if (xfer->rx_buf)
-- 
2.27.0


  reply index

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-31  7:59 [PATCH 0/8] spi: dw-dma: Add max SG entries burst capability support Serge Semin
2020-07-31  7:59 ` Serge Semin [this message]
2020-07-31  7:59 ` [PATCH 2/8] spi: dw-dma: Fail DMA-based transfer if no Tx-buffer specified Serge Semin
2020-07-31  7:59 ` [PATCH 3/8] spi: dw-dma: Configure the DMA channels in dma_setup Serge Semin
2020-07-31  9:16   ` Andy Shevchenko
2020-07-31 12:32     ` Serge Semin
2020-07-31  7:59 ` [PATCH 4/8] spi: dw-dma: Move DMA transfers submission to the channels prep methods Serge Semin
2020-07-31  9:15   ` Andy Shevchenko
2020-07-31 12:46     ` Serge Semin
2020-07-31  7:59 ` [PATCH 5/8] spi: dw-dma: Detach DMA transfer into a dedicated method Serge Semin
2020-07-31  7:59 ` [PATCH 6/8] spi: dw-dma: Move DMAC register cleanup to DMA transfer method Serge Semin
2020-07-31  7:59 ` [PATCH 7/8] spi: dw-dma: Pass exact data to the DMA submit and wait methods Serge Semin
2020-07-31  7:59 ` [PATCH 8/8] spi: dw-dma: Add one-by-one SG list entries transfer Serge Semin
2020-07-31  9:26 ` [PATCH 0/8] spi: dw-dma: Add max SG entries burst capability support Andy Shevchenko
2020-07-31 12:59   ` Serge Semin
2020-08-04 21:14     ` Mark Brown
2020-08-05 11:31       ` Vinod Koul

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