can: mcp251x: add support for half duplex controllers

Some SPI host controllers do not support full-duplex SPI and are
marked as such via the SPI_CONTROLLER_HALF_DUPLEX controller flag.

For such controllers use half duplex transactions but retain full
duplex transactions for the controllers that can handle those.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Link: https://lore.kernel.org/r/1595516275-1179-1-git-send-email-tharvey@gateworks.com
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

diff --git a/drivers/net/can/spi/mcp251x.c b/drivers/net/can/spi/mcp251x.c
index 3bf57bc9b3ff049507f4d909628e461c3fe35463..22d814ae4edcd30b1bc4d6ae658e0d5936b62a47 100644 (file)
--- a/drivers/net/can/spi/mcp251x.c
+++ b/drivers/net/can/spi/mcp251x.c
@@ -322,8 +322,12 @@ static u8 mcp251x_read_reg(struct spi_device *spi, u8 reg)
        priv->spi_tx_buf[0] = INSTRUCTION_READ;
        priv->spi_tx_buf[1] = reg;
 
-       mcp251x_spi_trans(spi, 3);
-       val = priv->spi_rx_buf[2];
+       if (spi->controller->flags & SPI_CONTROLLER_HALF_DUPLEX) {
+               spi_write_then_read(spi, priv->spi_tx_buf, 2, &val, 1);
+       } else {
+               mcp251x_spi_trans(spi, 3);
+               val = priv->spi_rx_buf[2];
+       }
 
        return val;
 }
@@ -335,10 +339,18 @@ static void mcp251x_read_2regs(struct spi_device *spi, u8 reg, u8 *v1, u8 *v2)
        priv->spi_tx_buf[0] = INSTRUCTION_READ;
        priv->spi_tx_buf[1] = reg;
 
-       mcp251x_spi_trans(spi, 4);
+       if (spi->controller->flags & SPI_CONTROLLER_HALF_DUPLEX) {
+               u8 val[2] = { 0 };
 
-       *v1 = priv->spi_rx_buf[2];
-       *v2 = priv->spi_rx_buf[3];
+               spi_write_then_read(spi, priv->spi_tx_buf, 2, val, 2);
+               *v1 = val[0];
+               *v2 = val[1];
+       } else {
+               mcp251x_spi_trans(spi, 4);
+
+               *v1 = priv->spi_rx_buf[2];
+               *v2 = priv->spi_rx_buf[3];
+       }
 }
 
 static void mcp251x_write_reg(struct spi_device *spi, u8 reg, u8 val)
@@ -657,8 +669,16 @@ static void mcp251x_hw_rx_frame(struct spi_device *spi, u8 *buf,
                        buf[i] = mcp251x_read_reg(spi, RXBCTRL(buf_idx) + i);
        } else {
                priv->spi_tx_buf[RXBCTRL_OFF] = INSTRUCTION_READ_RXB(buf_idx);
-               mcp251x_spi_trans(spi, SPI_TRANSFER_BUF_LEN);
-               memcpy(buf, priv->spi_rx_buf, SPI_TRANSFER_BUF_LEN);
+               if (spi->controller->flags & SPI_CONTROLLER_HALF_DUPLEX) {
+                       spi_write_then_read(spi, priv->spi_tx_buf, 1,
+                                           priv->spi_rx_buf,
+                                           SPI_TRANSFER_BUF_LEN);
+                       memcpy(buf + 1, priv->spi_rx_buf,
+                              SPI_TRANSFER_BUF_LEN - 1);
+               } else {
+                       mcp251x_spi_trans(spi, SPI_TRANSFER_BUF_LEN);
+                       memcpy(buf, priv->spi_rx_buf, SPI_TRANSFER_BUF_LEN);
+               }
        }
 }