[RFC PATCH] spi: omap2-mcspi: disable other channels CHCONF_FORCE in prepare_message

[Neil Armstrong <narmstrong@baylibre.com>]

Since the "Switch driver to use transfer_one" change, the cs_change
behavior has changed and a channel chip select can still be
asserted when changing channel from a previous last transfer in s
message having the cs_change attribute.

Since there is no sense having multiple chip select being asserted at the
same time, disable all the remaining forces chip selects in a the
prepare_message called right before a spi_transfer_one_message call.

This is also a bug fix found in the McSPI into a DM8168 SoC, hanging
all the other channels transfers when a CHCONF_FORCE is present.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
---
 drivers/spi/spi-omap2-mcspi.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

This is a patch RFC following the bug report :
'McSPI hangs with cs_change after "Switch driver to use transfer_one" change'
http://permalink.gmane.org/gmane.linux.kernel/2056841

diff --git a/drivers/spi/spi-omap2-mcspi.c b/drivers/spi/spi-omap2-mcspi.c
index 3d09e0b..db1b655 100644
--- a/drivers/spi/spi-omap2-mcspi.c
+++ b/drivers/spi/spi-omap2-mcspi.c
@@ -1217,6 +1217,33 @@ out:
 	return status;
 }

+static int omap2_mcspi_prepare_message(struct spi_master *master,
+				       struct spi_message *msg)
+{
+	struct omap2_mcspi	*mcspi = spi_master_get_devdata(master);
+	struct omap2_mcspi_regs	*ctx = &mcspi->ctx;
+	struct omap2_mcspi_cs	*cs;
+
+	/* Only a single channel can have the FORCE bit enabled
+	 * in its chconf0 register.
+	 * Scan all channels and disable them.
+	 * A FORCE can remain from a last transfer having cs_change enabled
+	 */
+
+	/* Ignore message */
+	(void)msg;
+
+	list_for_each_entry(cs, &ctx->cs, node) {
+		if ((cs->chconf0 & OMAP2_MCSPI_CHCONF_FORCE)) {
+			cs->chconf0 &= ~OMAP2_MCSPI_CHCONF_FORCE;
+			writel_relaxed(cs->chconf0,
+					cs->base + OMAP2_MCSPI_CHCONF0);
+		}
+	}
+
+	return 0;
+}
+
 static int omap2_mcspi_transfer_one(struct spi_master *master,
 		struct spi_device *spi, struct spi_transfer *t)
 {
@@ -1344,6 +1371,7 @@ static int omap2_mcspi_probe(struct platform_device *pdev)
 	master->bits_per_word_mask = SPI_BPW_RANGE_MASK(4, 32);
 	master->setup = omap2_mcspi_setup;
 	master->auto_runtime_pm = true;
+	master->prepare_message = omap2_mcspi_prepare_message;
 	master->transfer_one = omap2_mcspi_transfer_one;
 	master->set_cs = omap2_mcspi_set_cs;
 	master->cleanup = omap2_mcspi_cleanup;
-- 
1.9.1