spi: fsl-espi: add support for ESPI RXSKIP mode

This patch adds support for ESPI RXSKIP mode. This mode is optimized
for flash reads:
- sends a number of bytes and then reads a number of bytes
- shifts out zeros automatically when reading

Supporting RXSKIP mode is a prerequisite for supporting dual output
read mode.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-fsl-espi.c b/drivers/spi/spi-fsl-espi.c
index edb524f831a325eafcad7712c3c2bb9bd6b296e9..9ccbfbc75933ae3f38c09e84ae67ea4a734b0a4b 100644 (file)
--- a/drivers/spi/spi-fsl-espi.c
+++ b/drivers/spi/spi-fsl-espi.c
@@ -150,7 +150,8 @@ static void fsl_espi_copy_to_buf(struct spi_message *m,
        list_for_each_entry(t, &m->transfers, transfer_list) {
                if (t->tx_buf)
                        fsl_espi_memcpy_swab(buf, t->tx_buf, m, t);
-               else
+               /* In RXSKIP mode controller shifts out zeros internally */
+               else if (!mspi->rxskip)
                        memset(buf, 0, t->len);
                buf += t->len;
        }
@@ -203,6 +204,37 @@ static int fsl_espi_check_message(struct spi_message *m)
        return 0;
 }
 
+static unsigned int fsl_espi_check_rxskip_mode(struct spi_message *m)
+{
+       struct spi_transfer *t;
+       unsigned int i = 0, rxskip = 0;
+
+       /*
+        * prerequisites for ESPI rxskip mode:
+        * - message has two transfers
+        * - first transfer is a write and second is a read
+        *
+        * In addition the current low-level transfer mechanism requires
+        * that the rxskip bytes fit into the TX FIFO. Else the transfer
+        * would hang because after the first FSL_ESPI_FIFO_SIZE bytes
+        * the TX FIFO isn't re-filled.
+        */
+       list_for_each_entry(t, &m->transfers, transfer_list) {
+               if (i == 0) {
+                       if (!t->tx_buf || t->rx_buf ||
+                           t->len > FSL_ESPI_FIFO_SIZE)
+                               return 0;
+                       rxskip = t->len;
+               } else if (i == 1) {
+                       if (t->tx_buf || !t->rx_buf)
+                               return 0;
+               }
+               i++;
+       }
+
+       return i == 2 ? rxskip : 0;
+}
+
 static void fsl_espi_fill_tx_fifo(struct mpc8xxx_spi *mspi, u32 events)
 {
        u32 tx_fifo_avail;
@@ -281,7 +313,7 @@ static void fsl_espi_setup_transfer(struct spi_device *spi,
 static int fsl_espi_bufs(struct spi_device *spi, struct spi_transfer *t)
 {
        struct mpc8xxx_spi *mpc8xxx_spi = spi_master_get_devdata(spi->master);
-       u32 mask;
+       u32 mask, spcom;
        int ret;
 
        mpc8xxx_spi->rx_len = t->len;
@@ -293,8 +325,18 @@ static int fsl_espi_bufs(struct spi_device *spi, struct spi_transfer *t)
        reinit_completion(&mpc8xxx_spi->done);
 
        /* Set SPCOM[CS] and SPCOM[TRANLEN] field */
-       fsl_espi_write_reg(mpc8xxx_spi, ESPI_SPCOM,
-               (SPCOM_CS(spi->chip_select) | SPCOM_TRANLEN(t->len - 1)));
+       spcom = SPCOM_CS(spi->chip_select);
+       spcom |= SPCOM_TRANLEN(t->len - 1);
+
+       /* configure RXSKIP mode */
+       if (mpc8xxx_spi->rxskip) {
+               spcom |= SPCOM_RXSKIP(mpc8xxx_spi->rxskip);
+               mpc8xxx_spi->tx_len = mpc8xxx_spi->rxskip;
+               mpc8xxx_spi->rx_len = t->len - mpc8xxx_spi->rxskip;
+               mpc8xxx_spi->rx = t->rx_buf + mpc8xxx_spi->rxskip;
+       }
+
+       fsl_espi_write_reg(mpc8xxx_spi, ESPI_SPCOM, spcom);
 
        /* enable interrupts */
        mask = SPIM_DON;
@@ -326,6 +368,7 @@ static int fsl_espi_trans(struct spi_message *m, struct spi_transfer *trans)
        struct spi_device *spi = m->spi;
        int ret;
 
+       mspi->rxskip = fsl_espi_check_rxskip_mode(m);
        fsl_espi_copy_to_buf(m, mspi);
        fsl_espi_setup_transfer(spi, trans);
 

diff --git a/drivers/spi/spi-fsl-lib.h b/drivers/spi/spi-fsl-lib.h
index 35a7a1730d0c16d4f454a56285a9c701512821fa..3951322265d42b2b63c443d7dd89b737cca48c7f 100644 (file)
--- a/drivers/spi/spi-fsl-lib.h
+++ b/drivers/spi/spi-fsl-lib.h
@@ -31,6 +31,7 @@ struct mpc8xxx_spi {
 #if IS_ENABLED(CONFIG_SPI_FSL_ESPI)
        unsigned int rx_len;
        unsigned int tx_len;
+       unsigned int rxskip;
        u8 *local_buf;
        spinlock_t lock;
 #endif