2 files changed, 53 insertions, 0 deletions

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index bcdaa74f1c8e..bb7cf561c311 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -587,6 +587,49 @@ static int spi_map_msg(struct spi_master *master, struct spi_message *msg)
         struct device *dev = master->dev.parent;
         struct device *tx_dev, *rx_dev;
         struct spi_transfer *xfer;
+        void *tmp;
+        size_t max_tx, max_rx;
+
+        if (master->flags & (SPI_MASTER_MUST_RX | SPI_MASTER_MUST_TX)) {
+                max_tx = 0;
+                max_rx = 0;
+
+                list_for_each_entry(xfer, &msg->transfers, transfer_list) {
+                        if ((master->flags & SPI_MASTER_MUST_TX) &&
+                            !xfer->tx_buf)
+                                max_tx = max(xfer->len, max_tx);
+                        if ((master->flags & SPI_MASTER_MUST_RX) &&
+                            !xfer->rx_buf)
+                                max_rx = max(xfer->len, max_rx);
+                }
+
+                if (max_tx) {
+                        tmp = krealloc(master->dummy_tx, max_tx,
+                                       GFP_KERNEL | GFP_DMA);
+                        if (!tmp)
+                                return -ENOMEM;
+                        master->dummy_tx = tmp;
+                        memset(tmp, 0, max_tx);
+                }
+
+                if (max_rx) {
+                        tmp = krealloc(master->dummy_rx, max_rx,
+                                       GFP_KERNEL | GFP_DMA);
+                        if (!tmp)
+                                return -ENOMEM;
+                        master->dummy_rx = tmp;
+                }
+
+                if (max_tx || max_rx) {
+                        list_for_each_entry(xfer, &msg->transfers,
+                                            transfer_list) {
+                                if (!xfer->tx_buf)
+                                        xfer->tx_buf = master->dummy_tx;
+                                if (!xfer->rx_buf)
+                                        xfer->rx_buf = master->dummy_rx;
+                        }
+                }
+        }
 
         if (msg->is_dma_mapped || !master->can_dma)
                 return 0;
@@ -759,6 +802,10 @@ static void spi_pump_messages(struct kthread_work *work)
                 }
                 master->busy = false;
                 spin_unlock_irqrestore(&master->queue_lock, flags);
+                kfree(master->dummy_rx);
+                master->dummy_rx = NULL;
+                kfree(master->dummy_tx);
+                master->dummy_tx = NULL;
                 if (master->unprepare_transfer_hardware &&
                     master->unprepare_transfer_hardware(master))
                         dev_err(&master->dev,
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index b354dcbed55b..31a5b0ee93ec 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -347,6 +347,8 @@ struct spi_master {
 #define SPI_MASTER_HALF_DUPLEX  BIT(0)          /* can't do full duplex */
 #define SPI_MASTER_NO_RX        BIT(1)          /* can't do buffer read */
 #define SPI_MASTER_NO_TX        BIT(2)          /* can't do buffer write */
+#define SPI_MASTER_MUST_RX      BIT(3)          /* requires rx */
+#define SPI_MASTER_MUST_TX      BIT(4)          /* requires tx */
 
         /* lock and mutex for SPI bus locking */
         spinlock_t              bus_lock_spinlock;
@@ -443,6 +445,10 @@ struct spi_master {
         /* DMA channels for use with core dmaengine helpers */
         struct dma_chan         *dma_tx;
         struct dma_chan         *dma_rx;
+
+        /* dummy data for full duplex devices */
+        void                    *dummy_rx;
+        void                    *dummy_tx;
 };
 
 static inline void *spi_master_get_devdata(struct spi_master *master)