On Thu, 17 Dec 2020 12:28:44 -0800
Sowjanya Komatineni <skomatineni@xxxxxxxxxx> wrote:
> 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@xxxxxxxxxx>
> ---
> drivers/spi/spi-tegra210-quad.c | 41 ++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 40 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/spi/spi-tegra210-quad.c b/drivers/spi/spi-tegra210-quad.c
> index e7bee8d..695a296 100644
> --- 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 +978,8 @@ 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 *xfer, *next_xfer;
next_after should be declared where it's actually used.
> + bool use_hw_dummy_cycles = false;
I don't think you need this variable (see below).
> bool is_first_msg = true;
> int ret;
>
> @@ -984,8 +989,42 @@ static int tegra_qspi_transfer_one_message(struct spi_master *master, struct spi
> tqspi->rx_status = 0;
>
> list_for_each_entry(xfer, &msg->transfers, transfer_list) {
> + u8 dummy_cycles = 0;
Should be declared where it's actually used, and you don't want it to be a u8
since you're checking that the result does not exceed 255 which will always
be true with a u8.
> u32 cmd1;
>
> + /*
> + * Skip dummy bytes transfer if they are transferred by the hardware along
> + * with previous transfer.
> + */
> + if (xfer->dummy_data && use_hw_dummy_cycles) {
> + msg->actual_length += xfer->len;
> + continue;
> + }
> +
> + /*
> + * 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.
> + */
> + if (!list_is_last(&xfer->transfer_list, &msg->transfers)) {
> + next_xfer = list_next_entry(xfer, transfer_list);
> + if (next_xfer && next_xfer->dummy_data) {
> + dummy_cycles = next_xfer->len * 8 / next_xfer->tx_nbits;
> + use_hw_dummy_cycles = true;
> + /*
> + * Use software dummy bytes transfer if dummy cycles exceeds
> + * Tegra QSPI hardware maximum dummy cycles limit.
> + */
> + if (dummy_cycles > QSPI_DUMMY_CYCLES_MAX) {
> + use_hw_dummy_cycles = false;
> + dummy_cycles = 0;
> + }
> + }
> + }
> +
> + tqspi->dummy_cycles = dummy_cycles;
> +
This can be simplified:
/*
* Skip dummy bytes transfer if they were issued with the
* previous transfer.
*/
if (tqspi->dummy_cycles) {
WARN_ON(!xfer->dummy_data);
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.
*/
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;
}
}
> reinit_completion(&tqspi->xfer_completion);
>
> cmd1 = tegra_qspi_setup_transfer_one(spi, xfer, is_first_msg);
