On Tue, Mar 26, 2019 at 03:30:50PM +0100, Randolph Maaßen wrote:
> To transfer via SPI the tegra20-slink driver first sets the command
> register, which contains the chip select value, and after that the
> command2 register, which contains the chip select line. This leads to a
> small spike in the chip selct 0 line between the set of the value and
> the selection of the chip select line.
>
> This commit changes the order of the register writes so that first the
> chip select line is chosen and then the value is set, removing the
> spike.
>
> Signed-off-by: Randolph Maaßen <gaireg@xxxxxxxxx>
> ---
> drivers/spi/spi-tegra20-slink.c | 12 +++++++++---
> 1 file changed, 9 insertions(+), 3 deletions(-)
Looks good to me. Adding Sowjanya who has been looking into SPI
recently.
Thierry
> diff --git a/drivers/spi/spi-tegra20-slink.c b/drivers/spi/spi-tegra20-slink.c
> index 1427f343b39a..6d4679126213 100644
> --- a/drivers/spi/spi-tegra20-slink.c
> +++ b/drivers/spi/spi-tegra20-slink.c
> @@ -717,9 +717,6 @@ static int tegra_slink_start_transfer_one(struct spi_device *spi,
> command2 = tspi->command2_reg;
> command2 &= ~(SLINK_RXEN | SLINK_TXEN);
>
> - tegra_slink_writel(tspi, command, SLINK_COMMAND);
> - tspi->command_reg = command;
> -
> tspi->cur_direction = 0;
> if (t->rx_buf) {
> command2 |= SLINK_RXEN;
> @@ -729,9 +726,18 @@ static int tegra_slink_start_transfer_one(struct spi_device *spi,
> command2 |= SLINK_TXEN;
> tspi->cur_direction |= DATA_DIR_TX;
> }
> +
> + /*
> + * Writing to the command2 register bevore the command register prevents
> + * a spike in chip_select line 0. This selects the chip_select line
> + * before changing the chip_select value.
> + */
> tegra_slink_writel(tspi, command2, SLINK_COMMAND2);
> tspi->command2_reg = command2;
>
> + tegra_slink_writel(tspi, command, SLINK_COMMAND);
> + tspi->command_reg = command;
> +
> if (total_fifo_words > SLINK_FIFO_DEPTH)
> ret = tegra_slink_start_dma_based_transfer(tspi, t);
> else
> --
> 2.11.0
>
Attachment:
signature.asc
Description: PGP signature
