g: spi_controller: add the subtransaction capability

It is necessary to be able to send SPI transactions with sizes
exceeding the SPI controller buffer size. This can be achieved by
asserting CS before sending the first batch (data block) in a
transaction and deasserting CS after the last batch.

Let's add a SPI controller spi_sub_transaction() API, with an
additional parameter indicating when the last batch is submitted for
processing.

The existing spi_transaction() API becomes a wrapper which always
calls spi_sub_transaction() to send a full single batch transaction.

BUG=b:79492818
TEST='flashrom --flash-name' still succeeds.

Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Change-Id: Ia0c5114edd5caf6c6d0e22cab3bfa3c4d86ac79a
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2977964
Reviewed-by: Mary Ruthven <mruthven@chromium.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/include/spi.h b/include/spi.h
index 10286accab..b06f266d0c 100644
--- a/include/spi.h
+++ b/include/spi.h
@@ -85,6 +85,29 @@ int spi_transaction(const struct spi_device_t *spi_device,
 		    const uint8_t *txdata, int txlen,
 		    uint8_t *rxdata, int rxlen);
 
+/* Issue a part of SPI transaction.  Assumes SPI port has already been enabled.
+ *
+ * If CS is not asserted, asserts it first.
+ * Transmits <txlen> bytes from <txdata>, throwing away the corresponding
+ * received data, then transmits <rxlen> unused 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>.
+ * If 'final' is true, deasserts CS once transfer is completed.
+ *
+ * @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 or SPI_READBACK_ALL.
+ * @param deassert_cs flag indicating that CS needs to be deasserted in the
+ *                     end of this sub transaction.
+ */
+int spi_sub_transaction(const struct spi_device_t *spi_device,
+			const uint8_t *txdata, int txlen, uint8_t *rxdata,
+			int rxlen, bool deassert_cs);
+
 /* Similar to spi_transaction(), but hands over to DMA for reading response.
  * Must call spi_transaction_flush() after this to make sure the response is
  * received.