spi: extend spi master API on STM32

Extend the SPI master API to be able to do fancier transactions:
- allow to read the incoming bits while transmitting.
If SPI_READBACK_ALL is set in 'rxlen' when calling spi_transaction(),
then the received data during transmission is recorded in rxdata buffer
and the function assumes that the real 'rxlen' is equal to 'txlen'.
- add spi_transaction_wait() which is similar to spi_transaction_flush()
but without de-asserting the chip select, so we can chain several
transfers in a single transaction.

Implement them for STM32.

Signed-off-by: Vincent Palatin <vpalatin@chromium.org>

BRANCH=none
BUG=b:35648259
TEST=on Eve, use the FP sensor with the passthru.

Change-Id: Iebff617acd3230277d36a4f565766b7748721a1d
Reviewed-on: https://chromium-review.googlesource.com/452898
Commit-Ready: Vincent Palatin <vpalatin@chromium.org>
Tested-by: Vincent Palatin <vpalatin@chromium.org>
Reviewed-by: Todd Broch <tbroch@chromium.org>

1 files changed, 9 insertions, 1 deletions

diff --git a/include/spi.h b/include/spi.h
index 8fd7b2e311..49bddd3cc3 100644
--- a/include/spi.h
+++ b/include/spi.h
@@ -64,17 +64,22 @@ extern const unsigned int spi_devices_used;
  */
 int spi_enable(int port, int enable);
 
+#define SPI_READBACK_ALL (-1)
+
 /* Issue a SPI transaction.  Assumes SPI port has already been enabled.
  *
  * Transmits <txlen> bytes from <txdata>, throwing away the corresponding
  * received data, then transmits <rxlen> dummy bytes, saving the received data
  * in <rxdata>.
+ * If SPI_READBACK_ALL is set in <rxlen>, the received data during transmission
+ * is recorded in rxdata buffer and it assumes that the real <rxlen> is equal
+ * to <txlen>.
  *
  * @param spi_device  the SPI device to use
  * @param txdata  buffer to transmit
  * @param txlen  number of bytes in txdata.
  * @param rxdata  receive buffer.
- * @param rxlen  number of bytes in rxdata.
+ * @param rxlen  number of bytes in rxdata or SPI_READBACK_ALL.
  */
 int spi_transaction(const struct spi_device_t *spi_device,
 		    const uint8_t *txdata, int txlen,
@@ -91,6 +96,9 @@ int spi_transaction_async(const struct spi_device_t *spi_device,
 /* Wait for async response received */
 int spi_transaction_flush(const struct spi_device_t *spi_device);
 
+/* Wait for async response received but do not de-assert chip select */
+int spi_transaction_wait(const struct spi_device_t *spi_device);
+
 #ifdef CONFIG_SPI
 /**
  * Called when the NSS level changes, signalling the start or end of a SPI