[PATCH] SPI: per-transfer overrides for wordsize and clocking

Some protocols (like one for some bitmap displays) require different clock
speed or word size settings for each transfer in an SPI message. This adds
those parameters to struct spi_transfer.  They are to be used when they are
nonzero; otherwise the defaults from spi_device are to be used.

The patch also adds a setup_transfer callback to spi_bitbang, uses it for
messages that use those overrides, and implements it so that the pure
bitbanging code can help resolve any questions about how it should work.

Signed-off-by: Imre Deak <imre.deak@nokia.com>
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 63 insertions, 14 deletions

diff --git a/drivers/spi/spi_bitbang.c b/drivers/spi/spi_bitbang.c
index f037e55..0525c99 100644
--- a/drivers/spi/spi_bitbang.c
+++ b/drivers/spi/spi_bitbang.c
@@ -138,6 +138,43 @@ static unsigned bitbang_txrx_32(
 	return t->len - count;
 }
 
+static int
+bitbang_transfer_setup(struct spi_device *spi, struct spi_transfer *t)
+{
+	struct spi_bitbang_cs	*cs = spi->controller_state;
+	u8			bits_per_word;
+	u32			hz;
+
+	if (t) {
+		bits_per_word = t->bits_per_word;
+		hz = t->speed_hz;
+	} else {
+		bits_per_word = 0;
+		hz = 0;
+	}
+
+	/* spi_transfer level calls that work per-word */
+	if (!bits_per_word)
+		bits_per_word = spi->bits_per_word;
+	if (bits_per_word <= 8)
+		cs->txrx_bufs = bitbang_txrx_8;
+	else if (bits_per_word <= 16)
+		cs->txrx_bufs = bitbang_txrx_16;
+	else if (bits_per_word <= 32)
+		cs->txrx_bufs = bitbang_txrx_32;
+	else
+		return -EINVAL;
+
+	/* nsecs = (clock period)/2 */
+	if (!hz)
+		hz = spi->max_speed_hz;
+	cs->nsecs = (1000000000/2) / hz;
+	if (cs->nsecs > MAX_UDELAY_MS * 1000)
+		return -EINVAL;
+
+	return 0;
+}
+
 /**
  * spi_bitbang_setup - default setup for per-word I/O loops
  */
@@ -145,6 +182,7 @@ int spi_bitbang_setup(struct spi_device *spi)
 {
 	struct spi_bitbang_cs	*cs = spi->controller_state;
 	struct spi_bitbang	*bitbang;
+	int			retval;
 
 	if (!spi->max_speed_hz)
 		return -EINVAL;
@@ -160,25 +198,14 @@ int spi_bitbang_setup(struct spi_device *spi)
 	if (!spi->bits_per_word)
 		spi->bits_per_word = 8;
 
-	/* spi_transfer level calls that work per-word */
-	if (spi->bits_per_word <= 8)
-		cs->txrx_bufs = bitbang_txrx_8;
-	else if (spi->bits_per_word <= 16)
-		cs->txrx_bufs = bitbang_txrx_16;
-	else if (spi->bits_per_word <= 32)
-		cs->txrx_bufs = bitbang_txrx_32;
-	else
-		return -EINVAL;
-
 	/* per-word shift register access, in hardware or bitbanging */
 	cs->txrx_word = bitbang->txrx_word[spi->mode & (SPI_CPOL|SPI_CPHA)];
 	if (!cs->txrx_word)
 		return -EINVAL;
 
-	/* nsecs = (clock period)/2 */
-	cs->nsecs = (1000000000/2) / (spi->max_speed_hz);
-	if (cs->nsecs > MAX_UDELAY_MS * 1000)
-		return -EINVAL;
+	retval = bitbang_transfer_setup(spi, NULL);
+	if (retval < 0)
+		return retval;
 
 	dev_dbg(&spi->dev, "%s, mode %d, %u bits/w, %u nsec\n",
 			__FUNCTION__, spi->mode & (SPI_CPOL | SPI_CPHA),
@@ -246,6 +273,8 @@ static void bitbang_work(void *_bitbang)
 		unsigned		tmp;
 		unsigned		cs_change;
 		int			status;
+		int			(*setup_transfer)(struct spi_device *,
+						struct spi_transfer *);
 
 		m = container_of(bitbang->queue.next, struct spi_message,
 				queue);
@@ -262,6 +291,7 @@ static void bitbang_work(void *_bitbang)
 		tmp = 0;
 		cs_change = 1;
 		status = 0;
+		setup_transfer = NULL;
 
 		list_for_each_entry (t, &m->transfers, transfer_list) {
 			if (bitbang->shutdown) {
@@ -269,6 +299,20 @@ static void bitbang_work(void *_bitbang)
 				break;
 			}
 
+			/* override or restore speed and wordsize */
+			if (t->speed_hz || t->bits_per_word) {
+				setup_transfer = bitbang->setup_transfer;
+				if (!setup_transfer) {
+					status = -ENOPROTOOPT;
+					break;
+				}
+			}
+			if (setup_transfer) {
+				status = setup_transfer(spi, t);
+				if (status < 0)
+					break;
+			}
+
 			/* set up default clock polarity, and activate chip;
 			 * this implicitly updates clock and spi modes as
 			 * previously recorded for this device via setup().
@@ -325,6 +369,10 @@ static void bitbang_work(void *_bitbang)
 		m->status = status;
 		m->complete(m->context);
 
+		/* restore speed and wordsize */
+		if (setup_transfer)
+			setup_transfer(spi, NULL);
+
 		/* normally deactivate chipselect ... unless no error and
 		 * cs_change has hinted that the next message will probably
 		 * be for this chip too.
@@ -406,6 +454,7 @@ int spi_bitbang_start(struct spi_bitbang *bitbang)
 		bitbang->use_dma = 0;
 		bitbang->txrx_bufs = spi_bitbang_bufs;
 		if (!bitbang->master->setup) {
+			bitbang->setup_transfer = bitbang_transfer_setup;
 			bitbang->master->setup = spi_bitbang_setup;
 			bitbang->master->cleanup = spi_bitbang_cleanup;
 		}