[PATCH 0/6] spi: Add support for DMA transfers in sun4i SPI driver

[PATCH 0/6] spi: Add support for DMA transfers in sun4i SPI driver

[Sergey Suloev]

The following patchset provides corrections for PIO-mode
and support for DMA transfers in sun4i SPI driver.

Sergey Suloev (6):
  spi: core: handle timeout error from transfer_one()
  spi: sun4i: restrict transfer length in PIO-mode
  spi: sun4i: coding style/readability improvements
  spi: sun4i: use completion provided by SPI core driver
  spi: sun4i: introduce register set/unset helpers
  spi: sun4i: add DMA transfers support

 drivers/spi/spi-sun4i.c | 443 ++++++++++++++++++++++++++++++++++++------------
 drivers/spi/spi.c       |   5 +-
 2 files changed, 341 insertions(+), 107 deletions(-)

-- 
2.16.2

[PATCH 1/6] spi: core: handle timeout error from transfer_one()

[Sergey Suloev]

As long as sun4i/sun6i SPI drivers have overriden the default
"wait for completion" procedure then we need to properly
handle -ETIMEDOUT error from transfer_one().

Signed-off-by: Sergey Suloev <ssuloev@orpaltech.com>

---
 drivers/spi/spi.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index b33a727..2dcd4f6 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1028,7 +1028,7 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
 			reinit_completion(&ctlr->xfer_completion);
 
 			ret = ctlr->transfer_one(ctlr, msg->spi, xfer);
-			if (ret < 0) {
+			if (ret < 0 && ret != -ETIMEDOUT) {
 				SPI_STATISTICS_INCREMENT_FIELD(statm,
 							       errors);
 				SPI_STATISTICS_INCREMENT_FIELD(stats,
@@ -1051,7 +1051,7 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
 								 msecs_to_jiffies(ms));
 			}
 
-			if (ms == 0) {
+			if (ms == 0 || ret == -ETIMEDOUT) {
 				SPI_STATISTICS_INCREMENT_FIELD(statm,
 							       timedout);
 				SPI_STATISTICS_INCREMENT_FIELD(stats,
@@ -1059,6 +1059,7 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
 				dev_err(&msg->spi->dev,
 					"SPI transfer timed out\n");
 				msg->status = -ETIMEDOUT;
+				ret = 0;
 			}
 		} else {
 			if (xfer->len)
-- 
2.16.2

[PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Sergey Suloev]

There is no need to handle 3/4 empty/full interrupts
as the maximum supported transfer length in PIO mode
is 64 bytes for sun4i-family SoCs. As long as a
problem was reported previously with filling FIFO
on A10s then we stick with 63 bytes depth.

Signed-off-by: Sergey Suloev <ssuloev@orpaltech.com>

---
 drivers/spi/spi-sun4i.c | 50 ++++++++++++-------------------------------------
 1 file changed, 12 insertions(+), 38 deletions(-)

diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
index 4141003..2a49c22 100644
--- a/drivers/spi/spi-sun4i.c
+++ b/drivers/spi/spi-sun4i.c
@@ -22,7 +22,12 @@
 
 #include <linux/spi/spi.h>
 
-#define SUN4I_FIFO_DEPTH		64
+/*
+ * FIFO length is 64 bytes
+ * But filling the FIFO fully might cause a timeout
+ * on some devices, for example on spi2 on A10s
+ */
+#define SUN4I_FIFO_DEPTH		63
 
 #define SUN4I_RXDATA_REG		0x00
 
@@ -202,7 +207,7 @@ static void sun4i_spi_set_cs(struct spi_device *spi, bool enable)
 
 static size_t sun4i_spi_max_transfer_size(struct spi_device *spi)
 {
-	return SUN4I_FIFO_DEPTH - 1;
+	return SUN4I_FIFO_DEPTH;
 }
 
 static int sun4i_spi_transfer_one(struct spi_master *master,
@@ -216,11 +221,8 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
 	int ret = 0;
 	u32 reg;
 
-	/* We don't support transfer larger than the FIFO */
-	if (tfr->len > SUN4I_MAX_XFER_SIZE)
-		return -EMSGSIZE;
-
-	if (tfr->tx_buf && tfr->len >= SUN4I_MAX_XFER_SIZE)
+	/* We don't support transfers larger than FIFO depth */
+	if (tfr->len > SUN4I_FIFO_DEPTH)
 		return -EMSGSIZE;
 
 	reinit_completion(&sspi->done);
@@ -313,17 +315,11 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
 
 	/*
 	 * Fill the TX FIFO
-	 * Filling the FIFO fully causes timeout for some reason
-	 * at least on spi2 on A10s
 	 */
-	sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH - 1);
+	sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH);
 
-	/* Enable the interrupts */
-	sun4i_spi_enable_interrupt(sspi, SUN4I_INT_CTL_TC |
-					 SUN4I_INT_CTL_RF_F34);
-	/* Only enable Tx FIFO interrupt if we really need it */
-	if (tx_len > SUN4I_FIFO_DEPTH)
-		sun4i_spi_enable_interrupt(sspi, SUN4I_INT_CTL_TF_E34);
+	/* Enable the transfer complete interrupt */
+	sun4i_spi_enable_interrupt(sspi, SUN4I_INT_CTL_TC);
 
 	/* Start the transfer */
 	reg = sun4i_spi_read(sspi, SUN4I_CTL_REG);
@@ -363,28 +359,6 @@ static irqreturn_t sun4i_spi_handler(int irq, void *dev_id)
 		return IRQ_HANDLED;
 	}
 
-	/* Receive FIFO 3/4 full */
-	if (status & SUN4I_INT_CTL_RF_F34) {
-		sun4i_spi_drain_fifo(sspi, SUN4I_FIFO_DEPTH);
-		/* Only clear the interrupt _after_ draining the FIFO */
-		sun4i_spi_write(sspi, SUN4I_INT_STA_REG, SUN4I_INT_CTL_RF_F34);
-		return IRQ_HANDLED;
-	}
-
-	/* Transmit FIFO 3/4 empty */
-	if (status & SUN4I_INT_CTL_TF_E34) {
-		sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH);
-
-		if (!sspi->len)
-			/* nothing left to transmit */
-			sun4i_spi_disable_interrupt(sspi, SUN4I_INT_CTL_TF_E34);
-
-		/* Only clear the interrupt _after_ re-seeding the FIFO */
-		sun4i_spi_write(sspi, SUN4I_INT_STA_REG, SUN4I_INT_CTL_TF_E34);
-
-		return IRQ_HANDLED;
-	}
-
 	return IRQ_NONE;
 }
 
-- 
2.16.2

Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Maxime Ripard]

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On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:
> There is no need to handle 3/4 empty/full interrupts as the maximum
> supported transfer length in PIO mode is 64 bytes for sun4i-family
> SoCs.

That assumes that you'll be able to treat the FIFO full interrupt and
drain the FIFO before we have the next byte coming in. This would
require a real time system, and we're not in one of them.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Sergey Suloev]

On 04/03/2018 11:10 AM, Maxime Ripard wrote:
> On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:
>> There is no need to handle 3/4 empty/full interrupts as the maximum
>> supported transfer length in PIO mode is 64 bytes for sun4i-family
>> SoCs.
> That assumes that you'll be able to treat the FIFO full interrupt and
> drain the FIFO before we have the next byte coming in. This would
> require a real time system, and we're not in one of them.
>
> Maxime
>
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

so you think we should still handle 3/4 FIFO full ?

Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Sergey Suloev]

On 04/03/2018 11:10 AM, Maxime Ripard wrote:
> On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:
>> There is no need to handle 3/4 empty/full interrupts as the maximum
>> supported transfer length in PIO mode is 64 bytes for sun4i-family
>> SoCs.
> That assumes that you'll be able to treat the FIFO full interrupt and
> drain the FIFO before we have the next byte coming in. This would
> require a real time system, and we're not in one of them.
>
> Maxime
>
AFAIK in SPI protocol we send and receive at the same time. As soon as 
the transfer length

is <= FIFO depth then it means that at the moment we get TC interrupt 
all data for this transfer

sent/received already.

Is your point here that draining FIFO might be a long operation and we 
can lose next portion of data ?

Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Maxime Ripard]

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On Tue, Apr 03, 2018 at 02:08:43PM +0300, Sergey Suloev wrote:
> On 04/03/2018 11:10 AM, Maxime Ripard wrote:
> > On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:
> > > There is no need to handle 3/4 empty/full interrupts as the maximum
> > > supported transfer length in PIO mode is 64 bytes for sun4i-family
> > > SoCs.
> > That assumes that you'll be able to treat the FIFO full interrupt and
> > drain the FIFO before we have the next byte coming in. This would
> > require a real time system, and we're not in one of them.
>
> AFAIK in SPI protocol we send and receive at the same time.

It depends. The protocol allows it yes, but most devices I've seen can
only operate in half duplex. But it's not really the point.

> As soon as the transfer length is <= FIFO depth then it means that
> at the moment we get TC interrupt all data for this transfer
> sent/received already.
> 
> Is your point here that draining FIFO might be a long operation and we can
> lose next portion of data ?

My point is that, if you get another interrupt(s) right before the
FIFO full interrupt, that interrupt is going to be masked for as long
as it is needed for the previous handler(s) to execute.

If you're having another byte received while the interrupt is masked,
you're losing data.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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Re: [PATCH 2/6] spi: sun4i: restrict transfer length in PIO-mode

[Sergey Suloev]

On 04/03/2018 02:40 PM, Maxime Ripard wrote:
> On Tue, Apr 03, 2018 at 02:08:43PM +0300, Sergey Suloev wrote:
>> On 04/03/2018 11:10 AM, Maxime Ripard wrote:
>>> On Thu, Mar 29, 2018 at 09:59:03PM +0300, Sergey Suloev wrote:
>>>> There is no need to handle 3/4 empty/full interrupts as the maximum
>>>> supported transfer length in PIO mode is 64 bytes for sun4i-family
>>>> SoCs.
>>> That assumes that you'll be able to treat the FIFO full interrupt and
>>> drain the FIFO before we have the next byte coming in. This would
>>> require a real time system, and we're not in one of them.
>> AFAIK in SPI protocol we send and receive at the same time.
> It depends. The protocol allows it yes, but most devices I've seen can
> only operate in half duplex. But it's not really the point.
>
>> As soon as the transfer length is <= FIFO depth then it means that
>> at the moment we get TC interrupt all data for this transfer
>> sent/received already.
>>
>> Is your point here that draining FIFO might be a long operation and we can
>> lose next portion of data ?
> My point is that, if you get another interrupt(s) right before the
> FIFO full interrupt, that interrupt is going to be masked for as long
> as it is needed for the previous handler(s) to execute.
>
> If you're having another byte received while the interrupt is masked,
> you're losing data.
>
> Maxime
>
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

ok, I am going to put back 3/4 full handler then.

[PATCH 3/6] spi: sun4i: coding style/readability improvements

[Sergey Suloev]

Minor changes to fulfill the coding style and
improve the readability.

Signed-off-by: Sergey Suloev <ssuloev@orpaltech.com>

---
 drivers/spi/spi-sun4i.c | 32 +++++++++++++++++---------------
 1 file changed, 17 insertions(+), 15 deletions(-)

diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
index 2a49c22..2d716f1 100644
--- a/drivers/spi/spi-sun4i.c
+++ b/drivers/spi/spi-sun4i.c
@@ -83,8 +83,11 @@
 #define SUN4I_FIFO_STA_TF_CNT_MASK		0x7f
 #define SUN4I_FIFO_STA_TF_CNT_BITS		16
 
+#define SUN4I_SPI_MAX_SPEED_HZ		100 * 1000 * 1000
+#define SUN4I_SPI_MIN_SPEED_HZ		3 * 1000
+#define SUN4I_SPI_MODE_BITS		(SPI_CPOL | SPI_CPHA | SPI_CS_HIGH | SPI_LSB_FIRST)
+
 struct sun4i_spi {
-	struct spi_master	*master;
 	void __iomem		*base_addr;
 	struct clk		*hclk;
 	struct clk		*mclk;
@@ -409,12 +412,23 @@ static int sun4i_spi_probe(struct platform_device *pdev)
 	struct resource	*res;
 	int ret = 0, irq;
 
-	master = spi_alloc_master(&pdev->dev, sizeof(struct sun4i_spi));
+	master = spi_alloc_master(&pdev->dev, sizeof(*sspi));
 	if (!master) {
 		dev_err(&pdev->dev, "Unable to allocate SPI Master\n");
 		return -ENOMEM;
 	}
 
+	master->max_speed_hz = SUN4I_SPI_MAX_SPEED_HZ;
+	master->min_speed_hz = SUN4I_SPI_MIN_SPEED_HZ;
+	master->num_chipselect = 4;
+	master->mode_bits = SUN4I_SPI_MODE_BITS;
+	master->bits_per_word_mask = SPI_BPW_MASK(8);
+	master->set_cs = sun4i_spi_set_cs;
+	master->transfer_one = sun4i_spi_transfer_one;
+	master->max_transfer_size = sun4i_spi_max_transfer_size;
+	master->dev.of_node = pdev->dev.of_node;
+	master->auto_runtime_pm = true;
+
 	platform_set_drvdata(pdev, master);
 	sspi = spi_master_get_devdata(master);
 
@@ -433,24 +447,12 @@ static int sun4i_spi_probe(struct platform_device *pdev)
 	}
 
 	ret = devm_request_irq(&pdev->dev, irq, sun4i_spi_handler,
-			       0, "sun4i-spi", sspi);
+			       0, dev_name(&pdev->dev), sspi);
 	if (ret) {
 		dev_err(&pdev->dev, "Cannot request IRQ\n");
 		goto err_free_master;
 	}
 
-	sspi->master = master;
-	master->max_speed_hz = 100 * 1000 * 1000;
-	master->min_speed_hz = 3 * 1000;
-	master->set_cs = sun4i_spi_set_cs;
-	master->transfer_one = sun4i_spi_transfer_one;
-	master->num_chipselect = 4;
-	master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_CS_HIGH | SPI_LSB_FIRST;
-	master->bits_per_word_mask = SPI_BPW_MASK(8);
-	master->dev.of_node = pdev->dev.of_node;
-	master->auto_runtime_pm = true;
-	master->max_transfer_size = sun4i_spi_max_transfer_size;
-
 	sspi->hclk = devm_clk_get(&pdev->dev, "ahb");
 	if (IS_ERR(sspi->hclk)) {
 		dev_err(&pdev->dev, "Unable to acquire AHB clock\n");
-- 
2.16.2

[PATCH 4/6] spi: sun4i: use completion provided by SPI core driver

[Sergey Suloev]

As long as the completion already provided by the SPI core
then there is no need to waste extra-memory on this.
Also a waiting function was added to avoid code duplication.

Signed-off-by: Sergey Suloev <ssuloev@orpaltech.com>

---
 drivers/spi/spi-sun4i.c | 62 ++++++++++++++++++++++++++++---------------------
 1 file changed, 35 insertions(+), 27 deletions(-)

diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
index 2d716f1..4f24e12 100644
--- a/drivers/spi/spi-sun4i.c
+++ b/drivers/spi/spi-sun4i.c
@@ -92,8 +92,6 @@ struct sun4i_spi {
 	struct clk		*hclk;
 	struct clk		*mclk;
 
-	struct completion	done;
-
 	const u8		*tx_buf;
 	u8			*rx_buf;
 	int			len;
@@ -213,13 +211,36 @@ static size_t sun4i_spi_max_transfer_size(struct spi_device *spi)
 	return SUN4I_FIFO_DEPTH;
 }
 
+static int sun4i_spi_wait_for_transfer(struct spi_device *spi,
+				       struct spi_transfer *tfr)
+{
+	struct spi_master *master = spi->master;
+	unsigned int start, end, tx_time;
+	unsigned int timeout;
+
+	/* calc required timeout from given speed & len values */
+	tx_time = max(tfr->len * 8 * 2 / (tfr->speed_hz / 1000), 100U);
+	start = jiffies;
+	timeout = wait_for_completion_timeout(&master->xfer_completion,
+					      msecs_to_jiffies(tx_time));
+	end = jiffies;
+	if (!timeout) {
+		dev_warn(&master->dev,
+			 "%s: timeout transferring %u bytes@%iHz for %i(%i)ms",
+			 dev_name(&spi->dev), tfr->len, tfr->speed_hz,
+			 jiffies_to_msecs(end - start), tx_time);
+		return -ETIMEDOUT;
+	}
+
+	return 0;
+}
+
 static int sun4i_spi_transfer_one(struct spi_master *master,
 				  struct spi_device *spi,
 				  struct spi_transfer *tfr)
 {
 	struct sun4i_spi *sspi = spi_master_get_devdata(master);
-	unsigned int mclk_rate, div, timeout;
-	unsigned int start, end, tx_time;
+	unsigned int mclk_rate, div;
 	unsigned int tx_len = 0;
 	int ret = 0;
 	u32 reg;
@@ -228,7 +249,6 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
 	if (tfr->len > SUN4I_FIFO_DEPTH)
 		return -EMSGSIZE;
 
-	reinit_completion(&sspi->done);
 	sspi->tx_buf = tfr->tx_buf;
 	sspi->rx_buf = tfr->rx_buf;
 	sspi->len = tfr->len;
@@ -328,22 +348,8 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
 	reg = sun4i_spi_read(sspi, SUN4I_CTL_REG);
 	sun4i_spi_write(sspi, SUN4I_CTL_REG, reg | SUN4I_CTL_XCH);
 
-	tx_time = max(tfr->len * 8 * 2 / (tfr->speed_hz / 1000), 100U);
-	start = jiffies;
-	timeout = wait_for_completion_timeout(&sspi->done,
-					      msecs_to_jiffies(tx_time));
-	end = jiffies;
-	if (!timeout) {
-		dev_warn(&master->dev,
-			 "%s: timeout transferring %u bytes@%iHz for %i(%i)ms",
-			 dev_name(&spi->dev), tfr->len, tfr->speed_hz,
-			 jiffies_to_msecs(end - start), tx_time);
-		ret = -ETIMEDOUT;
-		goto out;
-	}
-
+	ret = sun4i_spi_wait_for_transfer(spi, tfr);
 
-out:
 	sun4i_spi_write(sspi, SUN4I_INT_CTL_REG, 0);
 
 	return ret;
@@ -351,14 +357,18 @@ out:
 
 static irqreturn_t sun4i_spi_handler(int irq, void *dev_id)
 {
-	struct sun4i_spi *sspi = dev_id;
-	u32 status = sun4i_spi_read(sspi, SUN4I_INT_STA_REG);
+	struct spi_master *master = dev_id;
+	struct sun4i_spi *sspi = spi_master_get_devdata(master);
+	u32 status;
+
+	status = sun4i_spi_read(sspi, SUN4I_INT_STA_REG);
 
 	/* Transfer complete */
 	if (status & SUN4I_INT_CTL_TC) {
-		sun4i_spi_write(sspi, SUN4I_INT_STA_REG, SUN4I_INT_CTL_TC);
+		sun4i_spi_write(sspi, SUN4I_INT_STA_REG,
+				SUN4I_INT_CTL_TC);
 		sun4i_spi_drain_fifo(sspi, SUN4I_FIFO_DEPTH);
-		complete(&sspi->done);
+		spi_finalize_current_transfer(master);
 		return IRQ_HANDLED;
 	}
 
@@ -447,7 +457,7 @@ static int sun4i_spi_probe(struct platform_device *pdev)
 	}
 
 	ret = devm_request_irq(&pdev->dev, irq, sun4i_spi_handler,
-			       0, dev_name(&pdev->dev), sspi);
+			       0, dev_name(&pdev->dev), master);
 	if (ret) {
 		dev_err(&pdev->dev, "Cannot request IRQ\n");
 		goto err_free_master;
@@ -467,8 +477,6 @@ static int sun4i_spi_probe(struct platform_device *pdev)
 		goto err_free_master;
 	}
 
-	init_completion(&sspi->done);
-
 	/*
 	 * This wake-up/shutdown pattern is to be able to have the
 	 * device woken up, even if runtime_pm is disabled
-- 
2.16.2

[PATCH 5/6] spi: sun4i: introduce register set/unset helpers

[Sergey Suloev]

Two helper functions were added in order to update
registers easily.

Signed-off-by: Sergey Suloev <ssuloev@orpaltech.com>

---
 drivers/spi/spi-sun4i.c | 40 +++++++++++++++++++---------------------
 1 file changed, 19 insertions(+), 21 deletions(-)

diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
index 4f24e12..fc913d4 100644
--- a/drivers/spi/spi-sun4i.c
+++ b/drivers/spi/spi-sun4i.c
@@ -107,29 +107,29 @@ static inline void sun4i_spi_write(struct sun4i_spi *sspi, u32 reg, u32 value)
 	writel(value, sspi->base_addr + reg);
 }
 
-static inline u32 sun4i_spi_get_tx_fifo_count(struct sun4i_spi *sspi)
+static inline void sun4i_spi_set(struct sun4i_spi *sspi, u32 addr, u32 val)
 {
-	u32 reg = sun4i_spi_read(sspi, SUN4I_FIFO_STA_REG);
-
-	reg >>= SUN4I_FIFO_STA_TF_CNT_BITS;
+	u32 reg = sun4i_spi_read(sspi, addr);
 
-	return reg & SUN4I_FIFO_STA_TF_CNT_MASK;
+	reg |= val;
+	sun4i_spi_write(sspi, addr, reg);
 }
 
-static inline void sun4i_spi_enable_interrupt(struct sun4i_spi *sspi, u32 mask)
+static inline void sun4i_spi_unset(struct sun4i_spi *sspi, u32 addr, u32 val)
 {
-	u32 reg = sun4i_spi_read(sspi, SUN4I_INT_CTL_REG);
+	u32 reg = sun4i_spi_read(sspi, addr);
 
-	reg |= mask;
-	sun4i_spi_write(sspi, SUN4I_INT_CTL_REG, reg);
+	reg &= ~val;
+	sun4i_spi_write(sspi, addr, reg);
 }
 
-static inline void sun4i_spi_disable_interrupt(struct sun4i_spi *sspi, u32 mask)
+static inline u32 sun4i_spi_get_tx_fifo_count(struct sun4i_spi *sspi)
 {
-	u32 reg = sun4i_spi_read(sspi, SUN4I_INT_CTL_REG);
+	u32 reg = sun4i_spi_read(sspi, SUN4I_FIFO_STA_REG);
 
-	reg &= ~mask;
-	sun4i_spi_write(sspi, SUN4I_INT_CTL_REG, reg);
+	reg >>= SUN4I_FIFO_STA_TF_CNT_BITS;
+
+	return reg & SUN4I_FIFO_STA_TF_CNT_MASK;
 }
 
 static inline void sun4i_spi_drain_fifo(struct sun4i_spi *sspi, int len)
@@ -256,13 +256,12 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
 	/* Clear pending interrupts */
 	sun4i_spi_write(sspi, SUN4I_INT_STA_REG, ~0);
 
+	/* Reset FIFOs */
+	sun4i_spi_set(sspi, SUN4I_CTL_REG,
+		      SUN4I_CTL_RF_RST | SUN4I_CTL_TF_RST);
 
 	reg = sun4i_spi_read(sspi, SUN4I_CTL_REG);
 
-	/* Reset FIFOs */
-	sun4i_spi_write(sspi, SUN4I_CTL_REG,
-			reg | SUN4I_CTL_RF_RST | SUN4I_CTL_TF_RST);
-
 	/*
 	 * Setup the transfer control register: Chip Select,
 	 * polarities, etc.
@@ -341,12 +340,11 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
 	 */
 	sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH);
 
-	/* Enable the transfer complete interrupt */
-	sun4i_spi_enable_interrupt(sspi, SUN4I_INT_CTL_TC);
+	/* Enable transfer complete interrupt */
+	sun4i_spi_set(sspi, SUN4I_INT_CTL_REG, SUN4I_INT_CTL_TC);
 
 	/* Start the transfer */
-	reg = sun4i_spi_read(sspi, SUN4I_CTL_REG);
-	sun4i_spi_write(sspi, SUN4I_CTL_REG, reg | SUN4I_CTL_XCH);
+	sun4i_spi_set(sspi, SUN4I_CTL_REG, SUN4I_CTL_XCH);
 
 	ret = sun4i_spi_wait_for_transfer(spi, tfr);
 
-- 
2.16.2

Re: [PATCH 5/6] spi: sun4i: introduce register set/unset helpers

[Maxime Ripard]

[-- Attachment #1: Type: text/plain, Size: 379 bytes --]

On Thu, Mar 29, 2018 at 09:59:06PM +0300, Sergey Suloev wrote:
> Two helper functions were added in order to update
> registers easily.
> 
> Signed-off-by: Sergey Suloev <ssuloev@orpaltech.com>

I'm not really sure what's easier about this one.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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Re: [PATCH 5/6] spi: sun4i: introduce register set/unset helpers

[Sergey Suloev]

On 04/03/2018 11:14 AM, Maxime Ripard wrote:
> On Thu, Mar 29, 2018 at 09:59:06PM +0300, Sergey Suloev wrote:
>> Two helper functions were added in order to update
>> registers easily.
>>
>> Signed-off-by: Sergey Suloev <ssuloev@orpaltech.com>
> I'm not really sure what's easier about this one.
>
> Maxime
>
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

well, just seems more readable vs doing "read, or, write" every time

[PATCH 6/6] spi: sun4i: add DMA transfers support

[Sergey Suloev]

DMA transfers are now available for sun4i-family SoCs.
The DMA mode is used automatically as soon as requested
transfer length is more than FIFO length.

Signed-off-by: Sergey Suloev <ssuloev@orpaltech.com>

---
 drivers/spi/spi-sun4i.c | 291 ++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 271 insertions(+), 20 deletions(-)

diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
index fc913d4..9928af7 100644
--- a/drivers/spi/spi-sun4i.c
+++ b/drivers/spi/spi-sun4i.c
@@ -14,6 +14,8 @@
 #include <linux/clk.h>
 #include <linux/delay.h>
 #include <linux/device.h>
+#include <linux/dmaengine.h>
+#include <linux/dma-mapping.h>
 #include <linux/interrupt.h>
 #include <linux/io.h>
 #include <linux/module.h>
@@ -39,6 +41,7 @@
 #define SUN4I_CTL_CPHA				BIT(2)
 #define SUN4I_CTL_CPOL				BIT(3)
 #define SUN4I_CTL_CS_ACTIVE_LOW			BIT(4)
+#define SUN4I_CTL_DMA_DEDICATED			BIT(5)
 #define SUN4I_CTL_LMTF				BIT(6)
 #define SUN4I_CTL_TF_RST			BIT(8)
 #define SUN4I_CTL_RF_RST			BIT(9)
@@ -58,6 +61,8 @@
 #define SUN4I_INT_STA_REG		0x10
 
 #define SUN4I_DMA_CTL_REG		0x14
+#define SUN4I_CTL_DMA_RF_READY			BIT(0)
+#define SUN4I_CTL_DMA_TF_NOT_FULL		BIT(10)
 
 #define SUN4I_WAIT_REG			0x18
 
@@ -169,6 +174,13 @@ static inline void sun4i_spi_fill_fifo(struct sun4i_spi *sspi, int len)
 	}
 }
 
+static bool sun4i_spi_can_dma(struct spi_master *master,
+			      struct spi_device *spi,
+			      struct spi_transfer *tfr)
+{
+	return tfr->len > SUN4I_FIFO_DEPTH;
+}
+
 static void sun4i_spi_set_cs(struct spi_device *spi, bool enable)
 {
 	struct sun4i_spi *sspi = spi_master_get_devdata(spi->master);
@@ -208,6 +220,11 @@ static void sun4i_spi_set_cs(struct spi_device *spi, bool enable)
 
 static size_t sun4i_spi_max_transfer_size(struct spi_device *spi)
 {
+	struct spi_master *master = spi->master;
+
+	if (master->can_dma)
+		return SUN4I_MAX_XFER_SIZE;
+
 	return SUN4I_FIFO_DEPTH;
 }
 
@@ -235,6 +252,160 @@ static int sun4i_spi_wait_for_transfer(struct spi_device *spi,
 	return 0;
 }
 
+static void sun4i_spi_dma_callback(void *param)
+{
+	struct spi_master *master = param;
+
+	dev_dbg(&master->dev, "DMA transfer complete\n");
+	spi_finalize_current_transfer(master);
+}
+
+static int sun4i_spi_dmap_prep_tx(struct spi_master *master,
+				  struct spi_transfer *tfr,
+				  dma_cookie_t *cookie)
+{
+	struct dma_async_tx_descriptor *chan_desc = NULL;
+
+	chan_desc = dmaengine_prep_slave_sg(master->dma_tx,
+					    tfr->tx_sg.sgl, tfr->tx_sg.nents,
+					    DMA_TO_DEVICE,
+					    DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
+	if (!chan_desc) {
+		dev_err(&master->dev,
+			"Couldn't prepare TX DMA slave\n");
+		return -EIO;
+	}
+
+	chan_desc->callback = sun4i_spi_dma_callback;
+	chan_desc->callback_param = master;
+
+	*cookie = dmaengine_submit(chan_desc);
+	dma_async_issue_pending(master->dma_tx);
+
+	return 0;
+}
+
+static int sun4i_spi_dmap_prep_rx(struct spi_master *master,
+				  struct spi_transfer *tfr,
+				  dma_cookie_t *cookie)
+{
+	struct dma_async_tx_descriptor *chan_desc = NULL;
+
+	chan_desc = dmaengine_prep_slave_sg(master->dma_rx,
+					    tfr->rx_sg.sgl, tfr->rx_sg.nents,
+					    DMA_FROM_DEVICE,
+					    DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
+	if (!chan_desc) {
+		dev_err(&master->dev,
+			"Couldn't prepare RX DMA slave\n");
+		return -EIO;
+	}
+
+	chan_desc->callback = sun4i_spi_dma_callback;
+	chan_desc->callback_param = master;
+
+	*cookie = dmaengine_submit(chan_desc);
+	dma_async_issue_pending(master->dma_rx);
+
+	return 0;
+}
+
+static int sun4i_spi_transfer_one_dma(struct spi_device *spi,
+				      struct spi_transfer *tfr)
+{
+	struct spi_master *master = spi->master;
+	struct sun4i_spi *sspi = spi_master_get_devdata(master);
+	dma_cookie_t tx_cookie = 0, rx_cookie = 0;
+	enum dma_status status;
+	int ret;
+	u32 reg = 0;
+
+	dev_dbg(&master->dev, "Using DMA mode for transfer\n");
+
+	if (sspi->tx_buf) {
+		ret = sun4i_spi_dmap_prep_tx(master, tfr, &tx_cookie);
+		if (ret)
+			goto out;
+
+		reg |= SUN4I_CTL_DMA_TF_NOT_FULL;
+	}
+
+	if (sspi->rx_buf) {
+		ret = sun4i_spi_dmap_prep_rx(master, tfr, &rx_cookie);
+		if (ret)
+			goto out;
+
+		reg |= SUN4I_CTL_DMA_RF_READY;
+	}
+
+	sun4i_spi_write(sspi, SUN4I_DMA_CTL_REG, reg);
+
+	/* Dedicated DMA requests */
+	sun4i_spi_set(sspi, SUN4I_CTL_REG, SUN4I_CTL_DMA_DEDICATED);
+
+	/* Start transfer */
+	sun4i_spi_set(sspi, SUN4I_CTL_REG, SUN4I_CTL_XCH);
+
+	/* Wait for completion */
+	ret = sun4i_spi_wait_for_transfer(spi, tfr);
+	if (ret)
+		goto out;
+
+	if (sspi->tx_buf && (status = dma_async_is_tx_complete(master->dma_tx,
+			tx_cookie, NULL, NULL))) {
+		dev_warn(&master->dev,
+			"DMA returned completion status of: %s\n",
+			status == DMA_ERROR ? "error" : "in progress");
+	}
+	if (sspi->rx_buf && (status = dma_async_is_tx_complete(master->dma_rx,
+			rx_cookie, NULL, NULL))) {
+		dev_warn(&master->dev,
+			"DMA returned completion status of: %s\n",
+			status == DMA_ERROR ? "error" : "in progress");
+	}
+
+out:
+	if (ret) {
+		dev_dbg(&master->dev, "DMA channel teardown\n");
+
+		if (sspi->tx_buf)
+			dmaengine_terminate_sync(master->dma_tx);
+		if (sspi->rx_buf)
+			dmaengine_terminate_sync(master->dma_rx);
+	}
+
+	sun4i_spi_drain_fifo(sspi, SUN4I_FIFO_DEPTH);
+
+	return ret;
+}
+
+static int sun4i_spi_transfer_one_pio(struct spi_device *spi,
+				      struct spi_transfer *tfr)
+{
+	struct spi_master *master = spi->master;
+	struct sun4i_spi *sspi = spi_master_get_devdata(master);
+	int ret;
+
+	/* Explicit disable DMA requests */
+	sun4i_spi_write(sspi, SUN4I_DMA_CTL_REG, 0);
+	sun4i_spi_unset(sspi, SUN4I_CTL_REG, SUN4I_CTL_DMA_DEDICATED);
+
+	/* Fill the TX FIFO */
+	sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH);
+
+	/* Enable transfer complete irq */
+	sun4i_spi_set(sspi, SUN4I_INT_CTL_REG, SUN4I_INT_CTL_TC);
+
+	/* Start transfer */
+	sun4i_spi_set(sspi, SUN4I_CTL_REG, SUN4I_CTL_XCH);
+
+	ret = sun4i_spi_wait_for_transfer(spi, tfr);
+
+	sun4i_spi_write(sspi, SUN4I_INT_CTL_REG, 0);
+
+	return ret;
+}
+
 static int sun4i_spi_transfer_one(struct spi_master *master,
 				  struct spi_device *spi,
 				  struct spi_transfer *tfr)
@@ -242,13 +413,22 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
 	struct sun4i_spi *sspi = spi_master_get_devdata(master);
 	unsigned int mclk_rate, div;
 	unsigned int tx_len = 0;
-	int ret = 0;
 	u32 reg;
 
-	/* We don't support transfers larger than FIFO depth */
-	if (tfr->len > SUN4I_FIFO_DEPTH)
+	/* A zero length transfer never finishes if programmed
+	   in the hardware */
+	if (!tfr->len)
+		return 0;
+
+	if (tfr->len > SUN4I_MAX_XFER_SIZE)
 		return -EMSGSIZE;
 
+	if (!master->can_dma) {
+		/* Don't support transfer larger than the FIFO */
+		if (tfr->len > SUN4I_FIFO_DEPTH)
+			return -EMSGSIZE;
+	}
+
 	sspi->tx_buf = tfr->tx_buf;
 	sspi->rx_buf = tfr->rx_buf;
 	sspi->len = tfr->len;
@@ -335,22 +515,10 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
 	sun4i_spi_write(sspi, SUN4I_BURST_CNT_REG, SUN4I_BURST_CNT(tfr->len));
 	sun4i_spi_write(sspi, SUN4I_XMIT_CNT_REG, SUN4I_XMIT_CNT(tx_len));
 
-	/*
-	 * Fill the TX FIFO
-	 */
-	sun4i_spi_fill_fifo(sspi, SUN4I_FIFO_DEPTH);
-
-	/* Enable transfer complete interrupt */
-	sun4i_spi_set(sspi, SUN4I_INT_CTL_REG, SUN4I_INT_CTL_TC);
-
-	/* Start the transfer */
-	sun4i_spi_set(sspi, SUN4I_CTL_REG, SUN4I_CTL_XCH);
-
-	ret = sun4i_spi_wait_for_transfer(spi, tfr);
-
-	sun4i_spi_write(sspi, SUN4I_INT_CTL_REG, 0);
+	if (sun4i_spi_can_dma(master, spi, tfr))
+		return sun4i_spi_transfer_one_dma(spi, tfr);
 
-	return ret;
+	return sun4i_spi_transfer_one_pio(spi, tfr);
 }
 
 static irqreturn_t sun4i_spi_handler(int irq, void *dev_id)
@@ -363,8 +531,7 @@ static irqreturn_t sun4i_spi_handler(int irq, void *dev_id)
 
 	/* Transfer complete */
 	if (status & SUN4I_INT_CTL_TC) {
-		sun4i_spi_write(sspi, SUN4I_INT_STA_REG,
-				SUN4I_INT_CTL_TC);
+		sun4i_spi_write(sspi, SUN4I_INT_STA_REG, SUN4I_INT_CTL_TC);
 		sun4i_spi_drain_fifo(sspi, SUN4I_FIFO_DEPTH);
 		spi_finalize_current_transfer(master);
 		return IRQ_HANDLED;
@@ -413,6 +580,76 @@ static int sun4i_spi_runtime_suspend(struct device *dev)
 	return 0;
 }
 
+static int sun4i_spi_dma_setup(struct device *dev,
+			       struct resource *res)
+{
+	struct spi_master *master = dev_get_drvdata(dev);
+	struct dma_slave_config dma_sconf;
+	int ret;
+
+	master->dma_tx = dma_request_slave_channel_reason(dev, "tx");
+	if (IS_ERR(master->dma_tx)) {
+		dev_err(dev, "Unable to acquire DMA TX channel\n");
+		ret = PTR_ERR(master->dma_tx);
+		goto out;
+	}
+
+	dma_sconf.direction = DMA_MEM_TO_DEV;
+	dma_sconf.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
+	dma_sconf.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
+	dma_sconf.dst_addr = res->start + SUN4I_TXDATA_REG;
+	dma_sconf.dst_maxburst = 1;
+	dma_sconf.src_maxburst = 1;
+
+	ret = dmaengine_slave_config(master->dma_tx, &dma_sconf);
+	if (ret) {
+		dev_err(dev, "Unable to configure DMA TX slave\n");
+		goto err_rel_tx;
+	}
+
+	master->dma_rx = dma_request_slave_channel_reason(dev, "rx");
+	if (IS_ERR(master->dma_rx)) {
+		dev_err(dev, "Unable to acquire DMA RX channel\n");
+		ret = PTR_ERR(master->dma_rx);
+		goto err_rel_tx;
+	}
+
+	dma_sconf.direction = DMA_DEV_TO_MEM;
+	dma_sconf.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
+	dma_sconf.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
+	dma_sconf.src_addr = res->start + SUN4I_RXDATA_REG;
+	dma_sconf.src_maxburst = 1;
+	dma_sconf.dst_maxburst = 1;
+
+	ret = dmaengine_slave_config(master->dma_rx, &dma_sconf);
+	if (ret) {
+		dev_err(dev, "Unable to configure DMA RX slave\n");
+		goto err_rel_rx;
+	}
+
+	/* don't set can_dma unless both channels are valid*/
+	master->can_dma = sun4i_spi_can_dma;
+
+	return 0;
+
+err_rel_rx:
+	dma_release_channel(master->dma_rx);
+err_rel_tx:
+	dma_release_channel(master->dma_tx);
+out:
+	master->dma_tx = NULL;
+	master->dma_rx = NULL;
+	return ret;
+}
+
+static void sun4i_spi_dma_release(struct spi_master *master)
+{
+	if (master->can_dma) {
+		dma_release_channel(master->dma_rx);
+		dma_release_channel(master->dma_tx);
+	}
+}
+
 static int sun4i_spi_probe(struct platform_device *pdev)
 {
 	struct spi_master *master;
@@ -475,6 +712,15 @@ static int sun4i_spi_probe(struct platform_device *pdev)
 		goto err_free_master;
 	}
 
+	ret = sun4i_spi_dma_setup(&pdev->dev, res);
+	if (ret) {
+		if (ret == -EPROBE_DEFER) {
+			/* wait for the dma driver to load */
+			goto err_free_master;
+		}
+		dev_warn(&pdev->dev, "DMA transfer not supported\n");
+	}
+
 	/*
 	 * This wake-up/shutdown pattern is to be able to have the
 	 * device woken up, even if runtime_pm is disabled
@@ -501,14 +747,19 @@ err_pm_disable:
 	pm_runtime_disable(&pdev->dev);
 	sun4i_spi_runtime_suspend(&pdev->dev);
 err_free_master:
+	sun4i_spi_dma_release(master);
 	spi_master_put(master);
 	return ret;
 }
 
 static int sun4i_spi_remove(struct platform_device *pdev)
 {
+	struct spi_master *master = platform_get_drvdata(pdev);
+
 	pm_runtime_force_suspend(&pdev->dev);
 
+	sun4i_spi_dma_release(master);
+
 	return 0;
 }
 
-- 
2.16.2

Re: [PATCH 6/6] spi: sun4i: add DMA transfers support

[Maxime Ripard]

[-- Attachment #1: Type: text/plain, Size: 1314 bytes --]

On Thu, Mar 29, 2018 at 09:59:07PM +0300, Sergey Suloev wrote:
> +static int sun4i_spi_dma_setup(struct device *dev,
> +			       struct resource *res)
> +{
> +	struct spi_master *master = dev_get_drvdata(dev);
> +	struct dma_slave_config dma_sconf;
> +	int ret;
> +
> +	master->dma_tx = dma_request_slave_channel_reason(dev, "tx");
> +	if (IS_ERR(master->dma_tx)) {
> +		dev_err(dev, "Unable to acquire DMA TX channel\n");
> +		ret = PTR_ERR(master->dma_tx);
> +		goto out;
> +	}
> +
> +	dma_sconf.direction = DMA_MEM_TO_DEV;
> +	dma_sconf.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
> +	dma_sconf.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;

I guess that would depend on the size of the transfer, right?

> +	dma_sconf.dst_addr = res->start + SUN4I_TXDATA_REG;
> +	dma_sconf.dst_maxburst = 1;
> +	dma_sconf.src_maxburst = 1;

And a burst of 1 seems sub-optimal here.

> +	ret = sun4i_spi_dma_setup(&pdev->dev, res);
> +	if (ret) {
> +		if (ret == -EPROBE_DEFER) {
> +			/* wait for the dma driver to load */
> +			goto err_free_master;
> +		}
> +		dev_warn(&pdev->dev, "DMA transfer not supported\n");

Saying why it's not supported would be great.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

[-- Attachment #2: signature.asc --]
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Re: [PATCH 6/6] spi: sun4i: add DMA transfers support

[Sergey Suloev]

On 04/03/2018 11:17 AM, Maxime Ripard wrote:
> On Thu, Mar 29, 2018 at 09:59:07PM +0300, Sergey Suloev wrote:
>> +static int sun4i_spi_dma_setup(struct device *dev,
>> +			       struct resource *res)
>> +{
>> +	struct spi_master *master = dev_get_drvdata(dev);
>> +	struct dma_slave_config dma_sconf;
>> +	int ret;
>> +
>> +	master->dma_tx = dma_request_slave_channel_reason(dev, "tx");
>> +	if (IS_ERR(master->dma_tx)) {
>> +		dev_err(dev, "Unable to acquire DMA TX channel\n");
>> +		ret = PTR_ERR(master->dma_tx);
>> +		goto out;
>> +	}
>> +
>> +	dma_sconf.direction = DMA_MEM_TO_DEV;
>> +	dma_sconf.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
>> +	dma_sconf.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
> I guess that would depend on the size of the transfer, right?
no
"this is the width in bytes of the source (RX)register where DMA data 
shall be read. If the sourceis memory this may be ignored depending on 
architecture."
AFAIK is should be 1 byte for SPI side and seems to be ignored for 
memory side, but as soon as I don't know what should be correct value 
for memory side I just put 1 there too.
>
>> +	dma_sconf.dst_addr = res->start + SUN4I_TXDATA_REG;
>> +	dma_sconf.dst_maxburst = 1;
>> +	dma_sconf.src_maxburst = 1;
> And a burst of 1 seems sub-optimal here.
I did some tests before with 3/4 FIFO size but it didn't work and I got 
stuck with 1 byte.
It seems like 1 byte is the correct value because in SPI protocol we can 
only send 1 byte in 1 burst.

>
>> +	ret = sun4i_spi_dma_setup(&pdev->dev, res);
>> +	if (ret) {
>> +		if (ret == -EPROBE_DEFER) {
>> +			/* wait for the dma driver to load */
>> +			goto err_free_master;
>> +		}
>> +		dev_warn(&pdev->dev, "DMA transfer not supported\n");
> Saying why it's not supported would be great.
I can put more info in this log
but there is already a message printed from sun4_spi_dma_setup() if any 
error occurs
>
> Maxime
>

Re: [PATCH 6/6] spi: sun4i: add DMA transfers support

[Maxime Ripard]

[-- Attachment #1: Type: text/plain, Size: 2500 bytes --]

On Tue, Apr 03, 2018 at 04:03:32PM +0300, Sergey Suloev wrote:
> On 04/03/2018 11:17 AM, Maxime Ripard wrote:
> > On Thu, Mar 29, 2018 at 09:59:07PM +0300, Sergey Suloev wrote:
> > > +static int sun4i_spi_dma_setup(struct device *dev,
> > > +			       struct resource *res)
> > > +{
> > > +	struct spi_master *master = dev_get_drvdata(dev);
> > > +	struct dma_slave_config dma_sconf;
> > > +	int ret;
> > > +
> > > +	master->dma_tx = dma_request_slave_channel_reason(dev, "tx");
> > > +	if (IS_ERR(master->dma_tx)) {
> > > +		dev_err(dev, "Unable to acquire DMA TX channel\n");
> > > +		ret = PTR_ERR(master->dma_tx);
> > > +		goto out;
> > > +	}
> > > +
> > > +	dma_sconf.direction = DMA_MEM_TO_DEV;
> > > +	dma_sconf.src_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
> > > +	dma_sconf.dst_addr_width = DMA_SLAVE_BUSWIDTH_1_BYTE;
> > I guess that would depend on the size of the transfer, right?
>
> no
> "this is the width in bytes of the source (RX)register where DMA data shall
> be read. If the sourceis memory this may be ignored depending on
> architecture."
> AFAIK is should be 1 byte for SPI side and seems to be ignored for memory
> side, but as soon as I don't know what should be correct value for memory
> side I just put 1 there too.

I meant the number of bits per word, sorry. That width would only
apply if you have 8 bits per word, but that seems to always be the
case. So nevermind.

> > > +	dma_sconf.dst_addr = res->start + SUN4I_TXDATA_REG;
> > > +	dma_sconf.dst_maxburst = 1;
> > > +	dma_sconf.src_maxburst = 1;
> >
> > And a burst of 1 seems sub-optimal here.
>
> I did some tests before with 3/4 FIFO size but it didn't work and I got
> stuck with 1 byte.
> It seems like 1 byte is the correct value because in SPI protocol we can
> only send 1 byte in 1 burst.

That's not about the SPI burst, it's about the DMA burst.

> > 
> > > +	ret = sun4i_spi_dma_setup(&pdev->dev, res);
> > > +	if (ret) {
> > > +		if (ret == -EPROBE_DEFER) {
> > > +			/* wait for the dma driver to load */
> > > +			goto err_free_master;
> > > +		}
> > > +		dev_warn(&pdev->dev, "DMA transfer not supported\n");
> > Saying why it's not supported would be great.
>
> I can put more info in this log
> but there is already a message printed from sun4_spi_dma_setup() if any
> error occurs

Then you don't need both.

Maxime

-- 
Maxime Ripard, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com

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