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>

2 files changed, 27 insertions, 6 deletions

diff --git a/chip/stm32/spi_master.c b/chip/stm32/spi_master.c
index c18191920a..647dcd9e7a 100644
--- a/chip/stm32/spi_master.c
+++ b/chip/stm32/spi_master.c
@@ -212,13 +212,20 @@ int spi_transaction_async(const struct spi_device_t *spi_device,
 {
 	int rv = EC_SUCCESS;
 	int port = spi_device->port;
+	int full_readback = 0;
 
 	stm32_spi_regs_t *spi = SPI_REGS[port];
 	char *buf;
 
-	rv = shared_mem_acquire(MAX(txlen, rxlen), &buf);
-	if (rv != EC_SUCCESS)
-		return rv;
+	if (rxlen == SPI_READBACK_ALL) {
+		buf = rxdata;
+		rxlen = txlen;
+		full_readback = 1;
+	} else {
+		rv = shared_mem_acquire(MAX(txlen, rxlen), &buf);
+		if (rv != EC_SUCCESS)
+			return rv;
+	}
 
 	/* Drive SS low */
 	gpio_set_level(spi_device->gpio_cs, 0);
@@ -235,14 +242,15 @@ int spi_transaction_async(const struct spi_device_t *spi_device,
 	if (rv != EC_SUCCESS)
 		goto err_free;
 
-	if (rxlen) {
+	if (!full_readback && rxlen) {
 		rv = spi_dma_start(port, buf, rxdata, rxlen);
 		if (rv != EC_SUCCESS)
 			goto err_free;
 	}
 
 err_free:
-	shared_mem_release(buf);
+	if (!full_readback)
+		shared_mem_release(buf);
 	return rv;
 }
 
@@ -256,6 +264,11 @@ int spi_transaction_flush(const struct spi_device_t *spi_device)
 	return rv;
 }
 
+int spi_transaction_wait(const struct spi_device_t *spi_device)
+{
+	return spi_dma_wait(spi_device->port);
+}
+
 int spi_transaction(const struct spi_device_t *spi_device,
 		    const uint8_t *txdata, int txlen,
 		    uint8_t *rxdata, int rxlen)
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