1 files changed, 6 insertions, 0 deletions

diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
index 240608cc7ae9..a461017ce5ce 100644
--- a/drivers/mmc/host/mmc_spi.c
+++ b/drivers/mmc/host/mmc_spi.c
@@ -1313,6 +1313,12 @@ static int mmc_spi_probe(struct spi_device *spi)
         struct mmc_spi_host     *host;
         int                     status;
 
+        /* We rely on full duplex transfers, mostly to reduce
+         * per-transfer overheads (by making fewer transfers).
+         */
+        if (spi->master->flags & SPI_MASTER_HALF_DUPLEX)
+                return -EINVAL;
+
         /* MMC and SD specs only seem to care that sampling is on the
          * rising edge ... meaning SPI modes 0 or 3.  So either SPI mode
          * should be legit.  We'll use mode 0 since the steady state is 0,