> 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 <[email protected]>
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 <[email protected]> > > --- > > 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 > >
