[PATCH v2 1/2] spi: introduce SPI_TRANS_FAIL_IO for error reporting

[Nam Cao]

The default message transfer implementation - spi_transfer_one_message -
invokes the specific device driver's transfer_one(), then waits for
completion. However, there is no mechanism for the device driver to
report failure in the middle of the transfer.

Introduce SPI_TRANS_FAIL_IO for drivers to report transfer failure.

Signed-off-by: Nam Cao <namcao@xxxxxxxxxxxxx>
Acked-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
---
v2: add document for this new flag

 drivers/spi/spi.c       |  3 +++
 include/linux/spi/spi.h | 12 ++++++++----
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 8ead7acb99f3..a4b8c07c5951 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1361,6 +1361,9 @@ static int spi_transfer_wait(struct spi_controller *ctlr,
 				"SPI transfer timed out\n");
 			return -ETIMEDOUT;
 		}
+
+		if (xfer->error & SPI_TRANS_FAIL_IO)
+			return -EIO;
 	}
 
 	return 0;
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 7b4baff63c5c..5d65a6273dcf 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -461,10 +461,13 @@ extern struct spi_device *spi_new_ancillary_device(struct spi_device *spi, u8 ch
  *                  - return 1 if the transfer is still in progress. When
  *                    the driver is finished with this transfer it must
  *                    call spi_finalize_current_transfer() so the subsystem
- *                    can issue the next transfer. Note: transfer_one and
- *                    transfer_one_message are mutually exclusive; when both
- *                    are set, the generic subsystem does not call your
- *                    transfer_one callback.
+ *                    can issue the next transfer. If the transfer fails, the
+ *                    driver must set the flag SPI_TRANS_FAIL_IO to
+ *                    spi_transfer->error first, before calling
+ *                    spi_finalize_current_transfer().
+ *                    Note: transfer_one and transfer_one_message are mutually
+ *                    exclusive; when both are set, the generic subsystem does
+ *                    not call your transfer_one callback.
  * @handle_err: the subsystem calls the driver to handle an error that occurs
  *		in the generic implementation of transfer_one_message().
  * @mem_ops: optimized/dedicated operations for interactions with SPI memory.
@@ -1040,6 +1043,7 @@ struct spi_transfer {
 	unsigned	len;
 
 #define SPI_TRANS_FAIL_NO_START	BIT(0)
+#define SPI_TRANS_FAIL_IO	BIT(1)
 	u16		error;
 
 	dma_addr_t	tx_dma;
-- 
2.39.2