> 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>
Very minor typo in the comment below:
Fix looks good as chip select need to be selected prior to asserting during
start of transfer.
Reviewed-by: Sowjanya Komatineni <skomatineni@xxxxxxxxxx>
> > ---
> > 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.
> > + */
Type "before"
> > 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
> >
