[PATCH v3 1/3] spi: Preserve preset cs_gpiod in __spi_add_device()

__spi_add_device() unconditionally overwrites spi->cs_gpiod[] from
ctlr->cs_gpiods[cs], even if the caller has already set a GPIO
descriptor on the device. This prevents drivers like
serial-multi-instantiate from pre-configuring a GPIO chip select
acquired from ACPI before adding the device.

Skip the overwrite when the device already has a cs_gpiod set for
the given index, allowing callers to preset GPIO chip selects that
aren't described in the controller's cs-gpios property.

This is useful on platforms where the ACPI _DSD cs-gpios property
on the SPI controller is incomplete, but the peripheral's ACPI node
does contain the correct GpioIo resource for its chip select.

Suggested-by: Richard Fitzgerald <rf@opensource.cirrus.com>
Signed-off-by: Khalil <redacted>
---
 drivers/spi/spi.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 07c572e1df..fbfb9a1aa2 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c

@@ -924,7 +924,8 @@ static int __spi_add_device(struct spi_device *spi, struct spi_device *parent)
 	if (ctlr->cs_gpiods) {
 		for (idx = 0; idx < spi->num_chipselect; idx++) {
 			cs = spi_get_chipselect(spi, idx);
-			spi_set_csgpiod(spi, idx, ctlr->cs_gpiods[cs]);
+			if (!spi_get_csgpiod(spi, idx))
+				spi_set_csgpiod(spi, idx, ctlr->cs_gpiods[cs]);
 		}
 	}
 

-- 
2.43.0