[PATCH v4 0/2] spi: atmel: add support to FIFOs and the internal chip-select

[PATCH v4 0/2] spi: atmel: add support to FIFOs and the internal chip-select

[Cyrille Pitchen]

ChangeLog

v4:
- remove the chip-select patch from the series as it has already been applied
- reword the commit message of the DT bindings patch to better explain why we
  use a new DT property, "atmel,fifo-size" instead of relying on the VERSION
  register or the "compatible" string.
- reword the commit message of the actual FIFO patch to better explain what
  are the MULTIPLE and SINGLE data modes and how to use them properly.
- add Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>

v3:
- replace "Alternative Command Mode" by "Chip Select Active After Transfer" in
  the DT bindings documentation. The "Alternative Command Mode" is a feature of
  the I2C controller.
- rename somes "size" variables to "num_data" to ease the distinction between
  the number of bytes and the number of data to transfer.

v2:
- read the Status Register to clear its RX FIFO Threshold Flag (RXFTHF) before
  writing into the IER to enable the RXFTHF interrupt.
- remove the reset of the FIFO Mode Register (FMR) at the end of transfers
  because setting the RX FIFO Threshold to 0 also sets the RXFTHF bit in SR.
- add a 3rd patch in the series to update the documentation of DT bindings.

v1:
This series of patches add support to features introduced by the Atmel sama5d2x
SoC

Cyrille Pitchen (2):
  spi: atmel: update DT bindings documentation
  spi: atmel: add support to FIFOs

 .../devicetree/bindings/spi/spi_atmel.txt          |   8 +-
 drivers/spi/spi-atmel.c                            | 255 ++++++++++++++++++++-
 2 files changed, 252 insertions(+), 11 deletions(-)

-- 
1.8.2.2

[PATCH v4 1/2] spi: atmel: update DT bindings documentation

[Cyrille Pitchen]

- add new property "atmel,fifo-size"
- change "cs-gpios" to optional for SPI controller version >= 2.

Please be aware that the VERSION register can not be used to guess the
size of FIFOs. Indeed, for a given hardware version, the SPI controller
can be integrated on Atmel SoCs with different FIFO sizes. Also the
"atmel,fifo-size" property is optional as older SPI controllers don't
embed FIFO at all.

Besides, the FIFO size can not be read or guessed from other registers:
When designing the FIFO feature, no dedicated registers were added to
store this size. Unused spaces in the I/O register range are limited and
better reserved for future usages. Instead, the FIFO size of each
peripheral is documented in the programmer datasheet.

Finally, on a given SoC, there can be several instances of the SPI
controller with different FIFO sizes. This explain why we'd rather use a
dedicated DT property than use the "compatible" property.

For instance, sama5d2x SoCs come with some SPI controllers, the ones
inside Flexcoms, integrating 32 data FIFOs whereas other SPI controllers
use 16 data FIFOs. All these SPI controllers share the same IP version.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
---
 Documentation/devicetree/bindings/spi/spi_atmel.txt | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/Documentation/devicetree/bindings/spi/spi_atmel.txt b/Documentation/devicetree/bindings/spi/spi_atmel.txt
index 4f8184d..fb588b3 100644
--- a/Documentation/devicetree/bindings/spi/spi_atmel.txt
+++ b/Documentation/devicetree/bindings/spi/spi_atmel.txt
@@ -4,11 +4,16 @@ Required properties:
 - compatible : should be "atmel,at91rm9200-spi".
 - reg: Address and length of the register set for the device
 - interrupts: Should contain spi interrupt
-- cs-gpios: chipselects
+- cs-gpios: chipselects (optional for SPI controller version >= 2 with the
+  Chip Select Active After Transfer feature).
 - clock-names: tuple listing input clock names.
 	Required elements: "spi_clk"
 - clocks: phandles to input clocks.
 
+Optional properties:
+- atmel,fifo-size: maximum number of data the RX and TX FIFOs can store for FIFO
+  capable SPI controllers.
+
 Example:
 
 spi1: spi at fffcc000 {
@@ -20,6 +25,7 @@ spi1: spi at fffcc000 {
 	clocks = <&spi1_clk>;
 	clock-names = "spi_clk";
 	cs-gpios = <&pioB 3 0>;
+	atmel,fifo-size = <32>;
 	status = "okay";
 
 	mmc-slot at 0 {
-- 
1.8.2.2

[PATCH v4 2/2] spi: atmel: add support to FIFOs

[Cyrille Pitchen]

The latest SPI controllers embedded inside sama5d2x SoCs come with FIFOs.
When FIFOs are enabled, they can either work in SINGLE data mode or
MULTIPLE data mode. The selected mode depends on the configuration of the
SPI controller (see below).

In SINGLE data mode (or legacy mode), for a single I/O access, only one
data can be read from the Receive Data Register (RDR) or written into the
Transmit Data Register (TDR). On the other hand, in MULTIPLE data mode, up
to 4 data can be read from the RDR or up 2 data can be written into the
TDR in a single 32bit I/O access. So programmers should take good care of
the width of the I/O access to read/write the right number of data. The
exact number of read/written data depends on both the I/O access width and
the data width (from 8 up to 16 bits).

To enable the FIFO feature a "atmel,fifo-size" property must be set to
provide the maximum number of data (not bytes) the RX and TX FIFOs can
store. Hence a 32 data FIFO can always store up to 32 data unrelated with
the actual data width.

When FIFOs are enabled, the RX one is forced to operate in SINGLE data
mode because this driver configures the spi controller as a master. In
master mode only, the Received Data Register has an additionnal Peripheral
Chip Select field, which prevents us from reading more than a single data
at each register access.

Besides, the TX FIFO operates in MULTIPLE data mode. However, even when a
8bit data size is used, only two data by access could be written into the
Transmit Data Register. Indeed the first data has to be written into the
lowest 16 bits whereas the second data has to be written into the highest
16 bits of the TDR. When DMA transfers are used to send data, we don't
rework the transmit buffer to cope with this hardware limitation: the
additional copies required to prepare a new input buffer suited to both
the DMA controller and the spi controller would waste all the benefit of
the DMA transfer. Instead, the DMA controller is configured to write only
one data at time into the TDR.

In pio mode, two data are written in the TDR in a single access.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
---
 drivers/spi/spi-atmel.c | 255 ++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 245 insertions(+), 10 deletions(-)

diff --git a/drivers/spi/spi-atmel.c b/drivers/spi/spi-atmel.c
index aa7d202..c9eca34 100644
--- a/drivers/spi/spi-atmel.c
+++ b/drivers/spi/spi-atmel.c
@@ -41,6 +41,8 @@
 #define SPI_CSR1				0x0034
 #define SPI_CSR2				0x0038
 #define SPI_CSR3				0x003c
+#define SPI_FMR					0x0040
+#define SPI_FLR					0x0044
 #define SPI_VERSION				0x00fc
 #define SPI_RPR					0x0100
 #define SPI_RCR					0x0104
@@ -62,6 +64,14 @@
 #define SPI_SWRST_SIZE				1
 #define SPI_LASTXFER_OFFSET			24
 #define SPI_LASTXFER_SIZE			1
+#define SPI_TXFCLR_OFFSET			16
+#define SPI_TXFCLR_SIZE				1
+#define SPI_RXFCLR_OFFSET			17
+#define SPI_RXFCLR_SIZE				1
+#define SPI_FIFOEN_OFFSET			30
+#define SPI_FIFOEN_SIZE				1
+#define SPI_FIFODIS_OFFSET			31
+#define SPI_FIFODIS_SIZE			1
 
 /* Bitfields in MR */
 #define SPI_MSTR_OFFSET				0
@@ -114,6 +124,22 @@
 #define SPI_TXEMPTY_SIZE			1
 #define SPI_SPIENS_OFFSET			16
 #define SPI_SPIENS_SIZE				1
+#define SPI_TXFEF_OFFSET			24
+#define SPI_TXFEF_SIZE				1
+#define SPI_TXFFF_OFFSET			25
+#define SPI_TXFFF_SIZE				1
+#define SPI_TXFTHF_OFFSET			26
+#define SPI_TXFTHF_SIZE				1
+#define SPI_RXFEF_OFFSET			27
+#define SPI_RXFEF_SIZE				1
+#define SPI_RXFFF_OFFSET			28
+#define SPI_RXFFF_SIZE				1
+#define SPI_RXFTHF_OFFSET			29
+#define SPI_RXFTHF_SIZE				1
+#define SPI_TXFPTEF_OFFSET			30
+#define SPI_TXFPTEF_SIZE			1
+#define SPI_RXFPTEF_OFFSET			31
+#define SPI_RXFPTEF_SIZE			1
 
 /* Bitfields in CSR0 */
 #define SPI_CPOL_OFFSET				0
@@ -157,6 +183,22 @@
 #define SPI_TXTDIS_OFFSET			9
 #define SPI_TXTDIS_SIZE				1
 
+/* Bitfields in FMR */
+#define SPI_TXRDYM_OFFSET			0
+#define SPI_TXRDYM_SIZE				2
+#define SPI_RXRDYM_OFFSET			4
+#define SPI_RXRDYM_SIZE				2
+#define SPI_TXFTHRES_OFFSET			16
+#define SPI_TXFTHRES_SIZE			6
+#define SPI_RXFTHRES_OFFSET			24
+#define SPI_RXFTHRES_SIZE			6
+
+/* Bitfields in FLR */
+#define SPI_TXFL_OFFSET				0
+#define SPI_TXFL_SIZE				6
+#define SPI_RXFL_OFFSET				16
+#define SPI_RXFL_SIZE				6
+
 /* Constants for BITS */
 #define SPI_BITS_8_BPT				0
 #define SPI_BITS_9_BPT				1
@@ -167,6 +209,9 @@
 #define SPI_BITS_14_BPT				6
 #define SPI_BITS_15_BPT				7
 #define SPI_BITS_16_BPT				8
+#define SPI_ONE_DATA				0
+#define SPI_TWO_DATA				1
+#define SPI_FOUR_DATA				2
 
 /* Bit manipulation macros */
 #define SPI_BIT(name) \
@@ -185,11 +230,31 @@
 	__raw_readl((port)->regs + SPI_##reg)
 #define spi_writel(port, reg, value) \
 	__raw_writel((value), (port)->regs + SPI_##reg)
+
+#define spi_readw(port, reg) \
+	__raw_readw((port)->regs + SPI_##reg)
+#define spi_writew(port, reg, value) \
+	__raw_writew((value), (port)->regs + SPI_##reg)
+
+#define spi_readb(port, reg) \
+	__raw_readb((port)->regs + SPI_##reg)
+#define spi_writeb(port, reg, value) \
+	__raw_writeb((value), (port)->regs + SPI_##reg)
 #else
 #define spi_readl(port, reg) \
 	readl_relaxed((port)->regs + SPI_##reg)
 #define spi_writel(port, reg, value) \
 	writel_relaxed((value), (port)->regs + SPI_##reg)
+
+#define spi_readw(port, reg) \
+	readw_relaxed((port)->regs + SPI_##reg)
+#define spi_writew(port, reg, value) \
+	writew_relaxed((value), (port)->regs + SPI_##reg)
+
+#define spi_readb(port, reg) \
+	readb_relaxed((port)->regs + SPI_##reg)
+#define spi_writeb(port, reg, value) \
+	writeb_relaxed((value), (port)->regs + SPI_##reg)
 #endif
 /* use PIO for small transfers, avoiding DMA setup/teardown overhead and
  * cache operations; better heuristics consider wordsize and bitrate.
@@ -252,6 +317,8 @@ struct atmel_spi {
 
 	bool			keep_cs;
 	bool			cs_active;
+
+	u32			fifo_size;
 };
 
 /* Controller-specific per-slave state */
@@ -410,6 +477,20 @@ static int atmel_spi_dma_slave_config(struct atmel_spi *as,
 	slave_config->dst_maxburst = 1;
 	slave_config->device_fc = false;
 
+	/*
+	 * This driver uses fixed peripheral select mode (PS bit set to '0' in
+	 * the Mode Register).
+	 * So according to the datasheet, when FIFOs are available (and
+	 * enabled), the Transmit FIFO operates in Multiple Data Mode.
+	 * In this mode, up to 2 data, not 4, can be written into the Transmit
+	 * Data Register in a single access.
+	 * However, the first data has to be written into the lowest 16 bits and
+	 * the second data into the highest 16 bits of the Transmit
+	 * Data Register. For 8bit data (the most frequent case), it would
+	 * require to rework tx_buf so each data would actualy fit 16 bits.
+	 * So we'd rather write only one data at the time. Hence the transmit
+	 * path works the same whether FIFOs are available (and enabled) or not.
+	 */
 	slave_config->direction = DMA_MEM_TO_DEV;
 	if (dmaengine_slave_config(as->dma.chan_tx, slave_config)) {
 		dev_err(&as->pdev->dev,
@@ -417,6 +498,14 @@ static int atmel_spi_dma_slave_config(struct atmel_spi *as,
 		err = -EINVAL;
 	}
 
+	/*
+	 * This driver configures the spi controller for master mode (MSTR bit
+	 * set to '1' in the Mode Register).
+	 * So according to the datasheet, when FIFOs are available (and
+	 * enabled), the Receive FIFO operates in Single Data Mode.
+	 * So the receive path works the same whether FIFOs are available (and
+	 * enabled) or not.
+	 */
 	slave_config->direction = DMA_DEV_TO_MEM;
 	if (dmaengine_slave_config(as->dma.chan_rx, slave_config)) {
 		dev_err(&as->pdev->dev,
@@ -506,10 +595,10 @@ static void dma_callback(void *data)
 }
 
 /*
- * Next transfer using PIO.
+ * Next transfer using PIO without FIFO.
  */
-static void atmel_spi_next_xfer_pio(struct spi_master *master,
-				struct spi_transfer *xfer)
+static void atmel_spi_next_xfer_single(struct spi_master *master,
+				       struct spi_transfer *xfer)
 {
 	struct atmel_spi	*as = spi_master_get_devdata(master);
 	unsigned long xfer_pos = xfer->len - as->current_remaining_bytes;
@@ -542,6 +631,99 @@ static void atmel_spi_next_xfer_pio(struct spi_master *master,
 }
 
 /*
+ * Next transfer using PIO with FIFO.
+ */
+static void atmel_spi_next_xfer_fifo(struct spi_master *master,
+				     struct spi_transfer *xfer)
+{
+	struct atmel_spi *as = spi_master_get_devdata(master);
+	u32 current_remaining_data, num_data;
+	u32 offset = xfer->len - as->current_remaining_bytes;
+	const u16 *words = (const u16 *)((u8 *)xfer->tx_buf + offset);
+	const u8  *bytes = (const u8  *)((u8 *)xfer->tx_buf + offset);
+	u16 td0, td1;
+	u32 fifomr;
+
+	dev_vdbg(master->dev.parent, "atmel_spi_next_xfer_fifo\n");
+
+	/* Compute the number of data to transfer in the current iteration */
+	current_remaining_data = ((xfer->bits_per_word > 8) ?
+				  ((u32)as->current_remaining_bytes >> 1) :
+				  (u32)as->current_remaining_bytes);
+	num_data = min(current_remaining_data, as->fifo_size);
+
+	/* Flush RX and TX FIFOs */
+	spi_writel(as, CR, SPI_BIT(RXFCLR) | SPI_BIT(TXFCLR));
+	while (spi_readl(as, FLR))
+		cpu_relax();
+
+	/* Set RX FIFO Threshold to the number of data to transfer */
+	fifomr = spi_readl(as, FMR);
+	spi_writel(as, FMR, SPI_BFINS(RXFTHRES, num_data, fifomr));
+
+	/* Clear FIFO flags in the Status Register, especially RXFTHF */
+	(void)spi_readl(as, SR);
+
+	/* Fill TX FIFO */
+	while (num_data >= 2) {
+		if (xfer->tx_buf) {
+			if (xfer->bits_per_word > 8) {
+				td0 = *words++;
+				td1 = *words++;
+			} else {
+				td0 = *bytes++;
+				td1 = *bytes++;
+			}
+		} else {
+			td0 = 0;
+			td1 = 0;
+		}
+
+		spi_writel(as, TDR, (td1 << 16) | td0);
+		num_data -= 2;
+	}
+
+	if (num_data) {
+		if (xfer->tx_buf) {
+			if (xfer->bits_per_word > 8)
+				td0 = *words++;
+			else
+				td0 = *bytes++;
+		} else {
+			td0 = 0;
+		}
+
+		spi_writew(as, TDR, td0);
+		num_data--;
+	}
+
+	dev_dbg(master->dev.parent,
+		"  start fifo xfer %p: len %u tx %p rx %p bitpw %d\n",
+		xfer, xfer->len, xfer->tx_buf, xfer->rx_buf,
+		xfer->bits_per_word);
+
+	/*
+	 * Enable RX FIFO Threshold Flag interrupt to be notified about
+	 * transfer completion.
+	 */
+	spi_writel(as, IER, SPI_BIT(RXFTHF) | SPI_BIT(OVRES));
+}
+
+/*
+ * Next transfer using PIO.
+ */
+static void atmel_spi_next_xfer_pio(struct spi_master *master,
+				    struct spi_transfer *xfer)
+{
+	struct atmel_spi *as = spi_master_get_devdata(master);
+
+	if (as->fifo_size)
+		atmel_spi_next_xfer_fifo(master, xfer);
+	else
+		atmel_spi_next_xfer_single(master, xfer);
+}
+
+/*
  * Submit next transfer for DMA.
  */
 static int atmel_spi_next_xfer_dma_submit(struct spi_master *master,
@@ -843,13 +1025,8 @@ static void atmel_spi_disable_pdc_transfer(struct atmel_spi *as)
 	spi_writel(as, PTCR, SPI_BIT(RXTDIS) | SPI_BIT(TXTDIS));
 }
 
-/* Called from IRQ
- *
- * Must update "current_remaining_bytes" to keep track of data
- * to transfer.
- */
 static void
-atmel_spi_pump_pio_data(struct atmel_spi *as, struct spi_transfer *xfer)
+atmel_spi_pump_single_data(struct atmel_spi *as, struct spi_transfer *xfer)
 {
 	u8		*rxp;
 	u16		*rxp16;
@@ -876,6 +1053,57 @@ atmel_spi_pump_pio_data(struct atmel_spi *as, struct spi_transfer *xfer)
 	}
 }
 
+static void
+atmel_spi_pump_fifo_data(struct atmel_spi *as, struct spi_transfer *xfer)
+{
+	u32 fifolr = spi_readl(as, FLR);
+	u32 num_bytes, num_data = SPI_BFEXT(RXFL, fifolr);
+	u32 offset = xfer->len - as->current_remaining_bytes;
+	u16 *words = (u16 *)((u8 *)xfer->rx_buf + offset);
+	u8  *bytes = (u8  *)((u8 *)xfer->rx_buf + offset);
+	u16 rd; /* RD field is the lowest 16 bits of RDR */
+
+	/* Update the number of remaining bytes to transfer */
+	num_bytes = ((xfer->bits_per_word > 8) ?
+		     (num_data << 1) :
+		     num_data);
+
+	if (as->current_remaining_bytes > num_bytes)
+		as->current_remaining_bytes -= num_bytes;
+	else
+		as->current_remaining_bytes = 0;
+
+	/* Handle odd number of bytes when data are more than 8bit width */
+	if (xfer->bits_per_word > 8)
+		as->current_remaining_bytes &= ~0x1;
+
+	/* Read data */
+	while (num_data) {
+		rd = spi_readl(as, RDR);
+		if (xfer->rx_buf) {
+			if (xfer->bits_per_word > 8)
+				*words++ = rd;
+			else
+				*bytes++ = rd;
+		}
+		num_data--;
+	}
+}
+
+/* Called from IRQ
+ *
+ * Must update "current_remaining_bytes" to keep track of data
+ * to transfer.
+ */
+static void
+atmel_spi_pump_pio_data(struct atmel_spi *as, struct spi_transfer *xfer)
+{
+	if (as->fifo_size)
+		atmel_spi_pump_fifo_data(as, xfer);
+	else
+		atmel_spi_pump_single_data(as, xfer);
+}
+
 /* Interrupt
  *
  * No need for locking in this Interrupt handler: done_status is the
@@ -916,7 +1144,7 @@ atmel_spi_pio_interrupt(int irq, void *dev_id)
 
 		complete(&as->xfer_completion);
 
-	} else if (pending & SPI_BIT(RDRF)) {
+	} else if (pending & (SPI_BIT(RDRF) | SPI_BIT(RXFTHF))) {
 		atmel_spi_lock(as);
 
 		if (as->current_remaining_bytes) {
@@ -1399,6 +1627,13 @@ static int atmel_spi_probe(struct platform_device *pdev)
 		spi_writel(as, PTCR, SPI_BIT(RXTDIS) | SPI_BIT(TXTDIS));
 	spi_writel(as, CR, SPI_BIT(SPIEN));
 
+	as->fifo_size = 0;
+	if (!of_property_read_u32(pdev->dev.of_node, "atmel,fifo-size",
+				  &as->fifo_size)) {
+		dev_info(&pdev->dev, "Using FIFO (%u data)\n", as->fifo_size);
+		spi_writel(as, CR, SPI_BIT(FIFOEN));
+	}
+
 	/* go! */
 	dev_info(&pdev->dev, "Atmel SPI Controller at 0x%08lx (irq %d)\n",
 			(unsigned long)regs->start, irq);
-- 
1.8.2.2