[PATCH] spi: set bits_per_word based on controller's bits_per_word_mask

[Alvaro Gamez Machado <alvaro.gamez@xxxxxxxxxx>]

By leaving this value unset, a default value of 8 was being set later on.

If it happens that the SPI master driver doesn't support this value of 8,
there will be an initial inconsistency between the SPI master and the device
itself. This isn't a problem for most devices because kernel drivers
associated to any device set the correct value themselves, but
for device drivers that do not change this value (such as spidev that
provides a userspace accesible device, which doesn't and can't know the
value it has to use), an error is raised:

xilinx_spi 44a10000.spi: can't setup spi1.0, status -22
spi_master spi1: spi_device register error /amba_pl/spi@44a10000/spidev@0
spi_master spi1: Failed to create SPI device for /amba_pl/spi@44a10000/spidev@0

When this happens, the expected /dev/spidevX.Y device isn't created,
and thus the user can't use the SPI_IOC_WR_BITS_PER_WORD ioctl to set the
desired value.

This change sets the initial value of bits_per to the smallest word that the
controller allows, so of_spi_parse_dt sets a value that is usable by the
controller.

Signed-off-by: Alvaro Gamez Machado <alvaro.gamez@xxxxxxxxxx>
---
 drivers/spi/spi.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index f9502dbbb5c1..794e20e54237 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1792,6 +1792,8 @@ static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
 	}
 	spi->max_speed_hz = value;
 
+	spi->bits_per_word = ffs(ctlr->bits_per_word_mask);
+
 	return 0;
 }
 
-- 
2.23.0