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This drives every native > active-low chip select low until tegra_spi_setup() runs for that device. >=20 > SPI children are registered and probed one at a time. A synchronous > probe of an earlier child can therefore transfer while a later child's > chip select is still asserted. On a Tegra234 system with active-low > devices on CS0 and CS1, this caused both devices to be selected when the > CS1 device probed first. Its initialization then intermittently failed. > A logic analyzer showed CS0 remained low throughout the CS1 transfer and > went high only after the CS1 probe failed. >=20 > Walk the controller's device tree children before SPI_COMMAND1 is > written and set CS_POL_INACTIVE for each native chip select a child > claims without spi-cs-high. That is the level tegra_spi_setup() programs > for the same device later, so the line is already deasserted when the > first child transfers and does not change level when setup runs. >=20 > Disabled children are walked too. The core only registers available > children, so tegra_spi_setup() never runs for a disabled one and probe > is the only chance to park its chip select at the level its hardware > needs. >=20 > Every other bit keeps the zero the driver has always written. A chip > select with no child in the device tree, one whose child asks for > spi-cs-high, and one driven by a GPIO are all left as before. > An > active-low device on a chip select the device tree does not describe is > therefore still asserted while a declared device probes, which is a > pre-existing problem this does not address. I don't think this is a problem, as the device tree is supposed to=20 describe the visible hardware. >=20 > Fixes: f333a331adfa ("spi/tegra114: add spi driver") > Assisted-by: Claude:Opus-5 > Signed-off-by: Abraham Zukor > --- > v2: derive the inactive level per chip select from the device tree rather > than setting the whole CS_POL_INACTIVE field. A single constant is wrong > for an active-high or a mixed-polarity bus, as Jon pointed out on v1. >=20 > Tested on a Jetson Orin Nano carrier board with active-low devices on CS0 > and CS1, and with the CS1 node disabled to confirm its chip select is > still parked inactive. >=20 > v1: https://lore.kernel.org/r/20260725042944.1204409-1-abe@maticrobots.co= m/ >=20 > drivers/spi/spi-tegra114.c | 25 +++++++++++++++++++++++++ > 1 file changed, 25 insertions(+) >=20 > diff --git a/drivers/spi/spi-tegra114.c b/drivers/spi/spi-tegra114.c > index aa44ffd09e61..d82b88c4fa9b 100644 > --- a/drivers/spi/spi-tegra114.c > +++ b/drivers/spi/spi-tegra114.c > @@ -1395,6 +1395,31 @@ static int tegra_spi_probe(struct platform_device = *pdev) > udelay(2); > reset_control_deassert(tspi->rst); > tspi->def_command1_reg =3D SPI_M_S; > + > + /* > + * SPI_COMMAND1 is written before any child is registered, so a chip > + * select with CS_POL_INACTIVE clear stays asserted until > + * tegra_spi_setup() runs for that device. Program the level the > + * device tree asks for up front instead. > + * > + * Disabled children are included deliberately. The core never > + * registers them, so this is the only chance to park their chip > + * select at the level their hardware needs. > + */ > + for_each_child_of_node_scoped(pdev->dev.of_node, np) { > + u32 cs; > + > + /* Only an active-low native chip select needs its bit set. */ > + if (of_property_read_bool(np, "spi-cs-high") || > + of_property_read_u32(np, "reg", &cs) || > + cs >=3D MAX_CHIP_SELECT || > + !of_parse_phandle_with_args(pdev->dev.of_node, "cs-gpios", > + "#gpio-cells", cs, NULL)) > + continue; > + > + tspi->def_command1_reg |=3D SPI_CS_POL_INACTIVE(cs); > + } Why do we need to consider cs-gpios? If a device has a cs-gpio, whatever=20 we program here wouldn't reach the device. The if condition is also very=20 difficult to read -- please use multiple if statements and normal error=20 handling patterns. Thanks Mikko > + > tegra_spi_writel(tspi, tspi->def_command1_reg, SPI_COMMAND1); > tspi->spi_cs_timing1 =3D tegra_spi_readl(tspi, SPI_CS_TIMING1); > tspi->spi_cs_timing2 =3D tegra_spi_readl(tspi, SPI_CS_TIMING2); > --=20 > 2.54.0 >=20 >=20