[PATCH v1] Make spi_ppc4xx.c tolerate 0 bits-per-word and 0 speed_hz

["Steven A. Falco" <sfalco@harris.com>]

If a SPI transfer is set up, but does not explicitly set bits-per-word
and speed_hz, then the transaction fails, because spi_ppc4xx_setupxfer
rejects it.

This patch modifies the logic to chose the struct spi_transfer parameters
only if they are non-zero.  Otherwise, the struct spi_device parameters
are used.

Additionally, since there is no OF binding for bits-per-word, we have to
tolerate the case where both t->bits_per_word and spi->bits_per_word are
zero.
---
This was brought to light by a pending patch to spi_bitbang, which results
in more calls to spi_ppc4xx_setupxfer.

 drivers/spi/spi_ppc4xx.c |   22 +++++++++++++++-------
 1 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/drivers/spi/spi_ppc4xx.c b/drivers/spi/spi_ppc4xx.c
index e46292b..9775bf2 100644
--- a/drivers/spi/spi_ppc4xx.c
+++ b/drivers/spi/spi_ppc4xx.c
@@ -151,16 +151,24 @@ static int spi_ppc4xx_setupxfer(struct spi_device *spi, struct spi_transfer *t)
 	/* Write new configration */
 	out_8(&hw->regs->mode, cs->mode);
 
+	/* Start with the generic configuration for this device. */
+	bpw = spi->bits_per_word;
+	cs->speed_hz = spi->max_speed_hz;
+
 	/*
-	 * Allow platform reduce the interrupt load on the CPU during SPI
-	 * transfers. We do not target maximum performance, but rather allow
-	 * platform to limit SPI bus frequency and interrupt rate.
+	 * Allow the platform to reduce the interrupt load on the CPU during
+	 * SPI transfers. We do not target maximum performance, but rather
+	 * allow the platform to limit SPI bus frequency and interrupt rate.
 	 */
-	bpw = t ? t->bits_per_word : spi->bits_per_word;
-	cs->speed_hz = t ? min(t->speed_hz, spi->max_speed_hz) :
-		spi->max_speed_hz;
+	if(t) {
+		if(t->bits_per_word)
+			bpw = t->bits_per_word;
+
+		if(t->speed_hz)
+			cs->speed_hz = min(t->speed_hz, spi->max_speed_hz);
+	}
 
-	if (bpw != 8) {
+	if (bpw && bpw != 8) {
 		dev_err(&spi->dev, "invalid bits-per-word (%d)\n", bpw);
 		return -EINVAL;
 	}
-- 
1.6.0.2