| Message ID | 20190426103007.29612-1-fancer.lancer@gmail.com (mailing list archive) |
|---|---|
| State | Accepted |
| Commit | d61ad23cb3be09ff4956e9b9794134456522817f |
| Headers | show |
| Series | spi: Clear SPI_CS_HIGH flag from bad_bits for GPIO chip-select | expand |
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c index 93986f879b09..49808892ef35 100644 --- a/drivers/spi/spi.c +++ b/drivers/spi/spi.c @@ -2943,6 +2943,11 @@ int spi_setup(struct spi_device *spi) * so it is ignored here. */ bad_bits = spi->mode & ~(spi->controller->mode_bits | SPI_CS_WORD); + /* nothing prevents from working with active-high CS in case if it + * is driven by GPIO. + */ + if (gpio_is_valid(spi->cs_gpio)) + bad_bits &= ~SPI_CS_HIGH; ugly_bits = bad_bits & (SPI_TX_DUAL | SPI_TX_QUAD | SPI_TX_OCTAL | SPI_RX_DUAL | SPI_RX_QUAD | SPI_RX_OCTAL);
When GPIO chip-select is used nothing prevents any available SPI controllers to work with both CS-high and traditional CS-low modes. In fact the SPI bus core code already does it, so we don't need to introduce any modification there. But spi_setup() still fails to switch the interface settings if CS-high flag is set for the case of GPIO-driven slave chip-select when the SPI controller doesn't support the hardwired CS-inversion. Lets fix it by clearing the SPI_CS_HIGH flag out from bad_bits (unsupported by controller) when client chip is selected by GPIO. This feature is useful for slave devices, which in accordance with communication protocol can work with both active-high and active-low chip-selects. I am aware of one such device. It is MMC-SPI interface, when at init sequence the driver needs to perform a read operation with low and high chip-select sequentially (requirement of 74 clock cycles with both chipselect, see the mmc_spi driver for details). Signed-off-by: Serge Semin <fancer.lancer@gmail.com> --- drivers/spi/spi.c | 5 +++++ 1 file changed, 5 insertions(+)