spi: xilinx: Convert to let spi core validate bits_per_word

Set bits_per_word_mask so spi core will reject transfers that attempt to use
an unsupported bits_per_word value.

spi_bitbang requires custom setup_transfer() to be defined if there is a
custom txrx_bufs(). Thus keep the empty xilinx_spi_setup_transfer() function
in the code.
Signed-off-by: NAxel Lin <axel.lin@ingics.com>
Acked-by: NMichal Simek <michal.simek@xilinx.com>
Signed-off-by: NMark Brown <broonie@linaro.org>

drivers/spi/spi-xilinx.c

@@ -209,26 +209,11 @@ static void xilinx_spi_chipselect(struct spi_device *spi, int is_on)
 }
 
 /* spi_bitbang requires custom setup_transfer() to be defined if there is a
- * custom txrx_bufs(). We have nothing to setup here as the SPI IP block
- * supports 8 or 16 bits per word which cannot be changed in software.
- * SPI clock can't be changed in software either.
- * Check for correct bits per word. Chip select delay calculations could be
- * added here as soon as bitbang_work() can be made aware of the delay value.
+ * custom txrx_bufs().
  */
 static int xilinx_spi_setup_transfer(struct spi_device *spi,
 		struct spi_transfer *t)
 {
-	struct xilinx_spi *xspi = spi_master_get_devdata(spi->master);
-	u8 bits_per_word;
-
-	bits_per_word = (t && t->bits_per_word)
-			 ? t->bits_per_word : spi->bits_per_word;
-	if (bits_per_word != xspi->bits_per_word) {
-		dev_err(&spi->dev, "%s, unsupported bits_per_word=%d\n",
-			__func__, bits_per_word);
-		return -EINVAL;
-	}
-
 	return 0;
 }
 
@@ -407,6 +392,7 @@ static int xilinx_spi_probe(struct platform_device *pdev)
 		xspi->write_fn = xspi_write32_be;
 	}
 
+	master->bits_per_word_mask = SPI_BPW_MASK(bits_per_word);
 	xspi->bits_per_word = bits_per_word;
 	if (xspi->bits_per_word == 8) {
 		xspi->tx_fn = xspi_tx8;