spi: tegra210-quad: Add support for hardware dummy cycles transfer

Tegra Quad SPI controller hardware supports sending dummy bytes based
on programmed dummy clock cycles after the actual transfer bytes.

This patch adds this support of hardware dummy bytes transfer and
skips transfer of dummy bytes from the software.

For dummy cycles more than Tegra Quad SPI hardware maximum dummy
cycles limit, driver transfers dummy bytes from the software.

Signed-off-by: Sowjanya Komatineni <skomatineni@nvidia.com>
Link: https://lore.kernel.org/r/1608585459-17250-7-git-send-email-skomatineni@nvidia.com
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-tegra210-quad.c b/drivers/spi/spi-tegra210-quad.c
index e7bee8d..2f806f4 100644 (file)
--- a/drivers/spi/spi-tegra210-quad.c
+++ b/drivers/spi/spi-tegra210-quad.c
@@ -117,6 +117,7 @@
 
 #define QSPI_MISC_REG                           0x194
 #define QSPI_NUM_DUMMY_CYCLE(x)                        (((x) & 0xff) << 0)
+#define QSPI_DUMMY_CYCLES_MAX                  0xff
 
 #define DATA_DIR_TX                            BIT(0)
 #define DATA_DIR_RX                            BIT(1)
@@ -170,6 +171,7 @@ struct tegra_qspi {
        u32                                     def_command2_reg;
        u32                                     spi_cs_timing1;
        u32                                     spi_cs_timing2;
+       u8                                      dummy_cycles;
 
        struct completion                       xfer_completion;
        struct spi_transfer                     *curr_xfer;
@@ -856,6 +858,8 @@ static int tegra_qspi_start_transfer_one(struct spi_device *spi,
 
        tqspi->command1_reg = command1;
 
+       tegra_qspi_writel(tqspi, QSPI_NUM_DUMMY_CYCLE(tqspi->dummy_cycles), QSPI_MISC_REG);
+
        ret = tegra_qspi_flush_fifos(tqspi, false);
        if (ret < 0)
                return ret;
@@ -974,7 +978,7 @@ static int tegra_qspi_transfer_one_message(struct spi_master *master, struct spi
 {
        struct tegra_qspi *tqspi = spi_master_get_devdata(master);
        struct spi_device *spi = msg->spi;
-       struct spi_transfer *xfer;
+       struct spi_transfer *transfer;
        bool is_first_msg = true;
        int ret;
 
@@ -983,9 +987,33 @@ static int tegra_qspi_transfer_one_message(struct spi_master *master, struct spi
        tqspi->tx_status = 0;
        tqspi->rx_status = 0;
 
-       list_for_each_entry(xfer, &msg->transfers, transfer_list) {
+       list_for_each_entry(transfer, &msg->transfers, transfer_list) {
+               struct spi_transfer *xfer = transfer;
+               u8 dummy_bytes = 0;
                u32 cmd1;
 
+               tqspi->dummy_cycles = 0;
+               /*
+                * Tegra QSPI hardware supports dummy bytes transfer after actual transfer
+                * bytes based on programmed dummy clock cycles in the QSPI_MISC register.
+                * So, check if the next transfer is dummy data transfer and program dummy
+                * clock cycles along with the current transfer and skip next transfer.
+                */
+               if (!list_is_last(&xfer->transfer_list, &msg->transfers)) {
+                       struct spi_transfer *next_xfer;
+
+                       next_xfer = list_next_entry(xfer, transfer_list);
+                       if (next_xfer->dummy_data) {
+                               u32 dummy_cycles = next_xfer->len * 8 / next_xfer->tx_nbits;
+
+                               if (dummy_cycles <= QSPI_DUMMY_CYCLES_MAX) {
+                                       tqspi->dummy_cycles = dummy_cycles;
+                                       dummy_bytes = next_xfer->len;
+                                       transfer = next_xfer;
+                               }
+                       }
+               }
+
                reinit_completion(&tqspi->xfer_completion);
 
                cmd1 = tegra_qspi_setup_transfer_one(spi, xfer, is_first_msg);
@@ -1016,7 +1044,7 @@ static int tegra_qspi_transfer_one_message(struct spi_master *master, struct spi
                        goto complete_xfer;
                }
 
-               msg->actual_length += xfer->len;
+               msg->actual_length += xfer->len + dummy_bytes;
 
 complete_xfer:
                if (ret < 0) {