[PATCH v4 3/8] spi: stm32: Add 'SPI_SIMPLEX_RX', 'SPI_3WIRE_RX' support for stm32f4

[dillon.minfei@gmail.com]

From: dillon min <dillon.minfei@gmail.com>

in l3gd20 driver startup, there is a setup failed error return from
stm32 spi driver

    "
    [    2.687630] st-gyro-spi spi0.0: supply vdd not found, using dummy
    regulator
    [    2.696869] st-gyro-spi spi0.0: supply vddio not found, using dummy
    regulator
    [    2.706707] spi_stm32 40015000.spi: SPI transfer setup failed
    [    2.713741] st-gyro-spi spi0.0: SPI transfer failed: -22
    [    2.721096] spi_master spi0: failed to transfer one message from queue
    [    2.729268] iio iio:device0: failed to read Who-Am-I register.
    [    2.737504] st-gyro-spi: probe of spi0.0 failed with error -22
    "

after debug into spi-stm32 driver, st-gyro-spi split two steps to read
l3gd20 id

first: send command to l3gd20 with read id command in tx_buf, rx_buf
is null.
second: read id with tx_buf is null, rx_buf not null.

so, for second step, stm32 driver recongise this process is 'SPI_SIMPLE_RX'
from stm32_spi_communication_type(), but there is no related process for this
type in stm32f4_spi_set_mode(), then we get error from
stm32_spi_transfer_one_setup().

we can use two method to fix this bug.
1, use stm32 spi's "In unidirectional receive-only mode (BIDIMODE=0 and
RXONLY=1)". but as our code running in sdram, the read latency is too large
to get so many receive overrun error in interrupts handler.

2, use stm32 spi's "In full-duplex (BIDIMODE=0 and RXONLY=0)", as tx_buf is
null, we must add dummy data sent out before read data.
so, add stm32f4_spi_tx_dummy() to handle this situation.

Signed-off-by: dillon min <dillon.minfei@gmail.com>
---
 drivers/spi/spi-stm32.c | 30 ++++++++++++++++++++++++++----
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi-stm32.c b/drivers/spi/spi-stm32.c
index 44ac6eb3..72d9387 100644
--- a/drivers/spi/spi-stm32.c
+++ b/drivers/spi/spi-stm32.c
@@ -388,6 +388,14 @@ static int stm32h7_spi_get_fifo_size(struct stm32_spi *spi)
 	return count;
 }
 
+static void stm32f4_spi_tx_dummy(struct stm32_spi *spi)
+{
+	if (spi->cur_bpw == 16)
+		writew_relaxed(0x5555, spi->base + STM32F4_SPI_DR);
+	else
+		writeb_relaxed(0x55, spi->base + STM32F4_SPI_DR);
+}
+
 /**
  * stm32f4_spi_get_bpw_mask - Return bits per word mask
  * @spi: pointer to the spi controller data structure
@@ -811,7 +819,9 @@ static irqreturn_t stm32f4_spi_irq_event(int irq, void *dev_id)
 		mask |= STM32F4_SPI_SR_TXE;
 	}
 
-	if (!spi->cur_usedma && spi->cur_comm == SPI_FULL_DUPLEX) {
+	if (!spi->cur_usedma && (spi->cur_comm == SPI_FULL_DUPLEX ||
+				spi->cur_comm == SPI_SIMPLEX_RX ||
+				spi->cur_comm == SPI_3WIRE_RX)) {
 		/* TXE flag is set and is handled when RXNE flag occurs */
 		sr &= ~STM32F4_SPI_SR_TXE;
 		mask |= STM32F4_SPI_SR_RXNE | STM32F4_SPI_SR_OVR;
@@ -850,8 +860,10 @@ static irqreturn_t stm32f4_spi_irq_event(int irq, void *dev_id)
 		stm32f4_spi_read_rx(spi);
 		if (spi->rx_len == 0)
 			end = true;
-		else /* Load data for discontinuous mode */
+		else if (spi->tx_buf)/* Load data for discontinuous mode */
 			stm32f4_spi_write_tx(spi);
+		else if (spi->cur_comm == SPI_SIMPLEX_RX)
+			stm32f4_spi_tx_dummy(spi);
 	}
 
 end_irq:
@@ -1151,7 +1163,9 @@ static int stm32f4_spi_transfer_one_irq(struct stm32_spi *spi)
 	/* Enable the interrupts relative to the current communication mode */
 	if (spi->cur_comm == SPI_SIMPLEX_TX || spi->cur_comm == SPI_3WIRE_TX) {
 		cr2 |= STM32F4_SPI_CR2_TXEIE;
-	} else if (spi->cur_comm == SPI_FULL_DUPLEX) {
+	} else if (spi->cur_comm == SPI_FULL_DUPLEX ||
+				spi->cur_comm == SPI_SIMPLEX_RX ||
+				spi->cur_comm == SPI_3WIRE_RX) {
 		/* In transmit-only mode, the OVR flag is set in the SR register
 		 * since the received data are never read. Therefore set OVR
 		 * interrupt only when rx buffer is available.
@@ -1170,6 +1184,8 @@ static int stm32f4_spi_transfer_one_irq(struct stm32_spi *spi)
 	/* starting data transfer when buffer is loaded */
 	if (spi->tx_buf)
 		stm32f4_spi_write_tx(spi);
+	else if (spi->cur_comm == SPI_SIMPLEX_RX)
+		stm32f4_spi_tx_dummy(spi);
 
 	spin_unlock_irqrestore(&spi->lock, flags);
 
@@ -1462,10 +1478,16 @@ static int stm32f4_spi_set_mode(struct stm32_spi *spi, unsigned int comm_type)
 		stm32_spi_set_bits(spi, STM32F4_SPI_CR1,
 					STM32F4_SPI_CR1_BIDIMODE |
 					STM32F4_SPI_CR1_BIDIOE);
-	} else if (comm_type == SPI_FULL_DUPLEX) {
+	} else if (comm_type == SPI_FULL_DUPLEX ||
+				comm_type == SPI_SIMPLEX_RX) {
 		stm32_spi_clr_bits(spi, STM32F4_SPI_CR1,
 					STM32F4_SPI_CR1_BIDIMODE |
 					STM32F4_SPI_CR1_BIDIOE);
+	} else if (comm_type == SPI_3WIRE_RX) {
+		stm32_spi_set_bits(spi, STM32F4_SPI_CR1,
+					STM32F4_SPI_CR1_BIDIMODE);
+		stm32_spi_clr_bits(spi, STM32F4_SPI_CR1,
+					STM32F4_SPI_CR1_BIDIOE);
 	} else {
 		return -EINVAL;
 	}
-- 
2.7.4