spi: core: Only check bits_per_word validity when explicitly provided

On SPI device probe, the core will call spi_setup in spi_add_device
before the corresponding driver was probed. When this happens, the
bits_per_word member of the device is not yet set by the driver,
resulting in the default being set to 8 bits-per-word.

However some controllers do not support 8 bits-per-word at all, which
results in a failure when checking the bits-per-word validity.

In order to support these devices, skip the bits-per-word validity
check when it is not explicitly provided by drivers.
Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Link: https://lore.kernel.org/r/20220412122207.130181-1-paul.kocialkowski@bootlin.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi.c

@@ -3513,13 +3513,18 @@ int spi_setup(struct spi_device *spi)
 		return -EINVAL;
 	}
 
-	if (!spi->bits_per_word)
+	if (!spi->bits_per_word) {
 		spi->bits_per_word = 8;
-
-	status = __spi_validate_bits_per_word(spi->controller,
-					      spi->bits_per_word);
-	if (status)
-		return status;
+	} else {
+		/*
+		 * Some controllers may not support the default 8 bits-per-word
+		 * so only perform the check when this is explicitly provided.
+		 */
+		status = __spi_validate_bits_per_word(spi->controller,
+						      spi->bits_per_word);
+		if (status)
+			return status;
+	}
 
 	if (spi->controller->max_speed_hz &&
 	    (!spi->max_speed_hz ||