drivers/spi/Kconfig and include/nuttx/spi/spi.h: Extend the HW features supported by SPI. It now supports a deffered DMA trigger hardware configuration. arch/arm/src/stm32/stm32_spi.c: Implements the new deferred DMA trigger feature.

arch/arm/src/stm32/stm32_spi.c

@@ -173,6 +173,10 @@ struct stm32_spidev_s
 #ifdef CONFIG_STM32_SPI_DMA
   volatile uint8_t rxresult;     /* Result of the RX DMA */
   volatile uint8_t txresult;     /* Result of the RX DMA */
+#ifdef CONFIG_SPI_TRIGGER
+  bool             defertrig;    /* Flag indicating that trigger should be deferred */
+  bool             trigarmed;    /* Flag indicating that the trigger is armed */
+#endif
   uint8_t          rxch;         /* The RX DMA channel number */
   uint8_t          txch;         /* The TX DMA channel number */
   DMA_HANDLE       rxdma;        /* DMA channel handle for RX transfers */
@@ -277,6 +281,9 @@ static const struct spi_ops_s g_sp1iops =
   .sndblock          = spi_sndblock,
   .recvblock         = spi_recvblock,
 #endif
+#ifdef CONFIG_SPI_TRIGGER
+  .trigger           = spi_trigger,
+#endif
 #ifdef CONFIG_SPI_CALLBACK
   .registercallback  = stm32_spi1register,  /* Provided externally */
 #else
@@ -326,6 +333,9 @@ static const struct spi_ops_s g_sp2iops =
   .sndblock          = spi_sndblock,
   .recvblock         = spi_recvblock,
 #endif
+#ifdef CONFIG_SPI_TRIGGER
+  .trigger           = spi_trigger,
+#endif
 #ifdef CONFIG_SPI_CALLBACK
   .registercallback  = stm32_spi2register,  /* provided externally */
 #else
@@ -375,6 +385,9 @@ static const struct spi_ops_s g_sp3iops =
   .sndblock          = spi_sndblock,
   .recvblock         = spi_recvblock,
 #endif
+#ifdef CONFIG_SPI_TRIGGER
+  .trigger           = spi_trigger,
+#endif
 #ifdef CONFIG_SPI_CALLBACK
   .registercallback  = stm32_spi3register,  /* provided externally */
 #else
@@ -424,6 +437,9 @@ static const struct spi_ops_s g_sp4iops =
   .sndblock          = spi_sndblock,
   .recvblock         = spi_recvblock,
 #endif
+#ifdef CONFIG_SPI_TRIGGER
+  .trigger           = spi_trigger,
+#endif
 #ifdef CONFIG_SPI_CALLBACK
   .registercallback  = stm32_spi4register,  /* provided externally */
 #else
@@ -473,6 +489,9 @@ static const struct spi_ops_s g_sp5iops =
   .sndblock          = spi_sndblock,
   .recvblock         = spi_recvblock,
 #endif
+#ifdef CONFIG_SPI_TRIGGER
+  .trigger           = spi_trigger,
+#endif
 #ifdef CONFIG_SPI_CALLBACK
   .registercallback  = stm32_spi5register,  /* provided externally */
 #else
@@ -522,6 +541,9 @@ static const struct spi_ops_s g_sp6iops =
   .sndblock          = spi_sndblock,
   .recvblock         = spi_recvblock,
 #endif
+#ifdef CONFIG_SPI_TRIGGER
+  .trigger           = spi_trigger,
+#endif
 #ifdef CONFIG_SPI_CALLBACK
   .registercallback  = stm32_spi6register,  /* provided externally */
 #else
@@ -1428,12 +1450,23 @@ static int spi_hwfeatures(FAR struct spi_dev_s *dev, spi_hwfeatures_t features)
   spi_modifycr1(priv, setbits, clrbits);
   spi_modifycr1(priv, SPI_CR1_SPE, 0);
 
+  features &= ~HWFEAT_LSBFIRST;
+#endif
+
+#ifdef CONFIG_SPI_TRIGGER
+/* Turn deferred trigger mode on or off.  Only applicable for DMA mode. If a
+ * transfer is deferred then the DMA will not actually be triggered until a
+ * subsequent call to SPI_TRIGGER to set it off. The thread will be waiting
+ * on the transfer completing as normal.
+ */
+
+  priv->defertrig = ((features & HWFEAT_TRIGGER) != 0);
+  features &= ~HWFEAT_TRIGGER;
+#endif
+
   /* Other H/W features are not supported */
 
-  return ((features & ~HWFEAT_LSBFIRST) == 0) ? OK : -ENOSYS;
+  return (features == 0) ? OK : -ENOSYS;
-#else
-  return -ENOSYS;
-#endif
 }
 #endif
 
@@ -1634,19 +1667,78 @@ static void spi_exchange(FAR struct spi_dev_s *dev, FAR const void *txbuffer,
       spi_dmarxsetup(priv, rxbuffer, &rxdummy, nwords);
       spi_dmatxsetup(priv, txbuffer, &txdummy, nwords);
 
+#ifdef CONFIG_SPI_TRIGGER
+      /* Is deferred triggering in effect? */
+
+      if (!priv->defertrig)
+        {
+          /* No.. Start the DMAs */
+
+          spi_dmarxstart(priv);
+          spi_dmatxstart(priv);
+        }
+      else
+        {
+          /* Yes.. indicated that we are ready to be started */
+
+          priv->trigarmed = true;
+        }
+#else
       /* Start the DMAs */
 
       spi_dmarxstart(priv);
       spi_dmatxstart(priv);
+#endif
 
       /* Then wait for each to complete */
 
       spi_dmarxwait(priv);
       spi_dmatxwait(priv);
+
+#ifdef CONFIG_SPI_TRIGGER
+      priv->trigarmed = false;
+#endif
     }
 }
 #endif /* CONFIG_STM32_SPI_DMA */
 
+/****************************************************************************
+ * Name: spi_trigger
+ *
+ * Description:
+ *   Trigger a previously configured DMA transfer.
+ *
+ * Input Parameters:
+ *   dev      - Device-specific state data
+ *
+ * Returned Value:
+ *   OK       - Trigger was fired
+ *   ENOTSUP  - Trigger not fired due to lack of DMA support
+ *   EIO      - Trigger not fired because not previously primed
+ *
+ ****************************************************************************/
+
+#ifdef CONFIG_SPI_TRIGGER
+static int spi_trigger(FAR struct spi_dev_s *dev)
+{
+#ifdef CONFIG_STM32_SPI_DMA
+  FAR struct stm32_spidev_s *priv = (FAR struct stm32_spidev_s *)dev;
+
+  if (!priv->trigarmed)
+    {
+      return -EIO;
+    }
+
+  spi_dmarxstart(priv);
+  spi_dmatxstart(priv);
+
+  return OK;
+#else
+  return -ENOSYS;
+#endif
+}
+#endif
+
 /****************************************************************************
  * Name: spi_sndblock
  *

drivers/spi/Kconfig

@@ -114,6 +114,17 @@ config SPI_CS_DELAY_CONTROL
 
 		This option enables the setdelay() interface method.
 
+config SPI_TRIGGER
+	bool "SPI DMA trigger"
+	default n
+	select SPI_HWFEATURES
+	depends on SPI_EXCHANGE
+	---help---
+		Some architectures benefit from delaying the start of DMA from the
+		DMA setup.  If this option is selected, then an SPI_TRIGGER() method
+		is supported:  The DMA is setup with in in SPI_EXCHANGE() but does
+		not actually begin until SPI_TRIGGER() is called.
+
 config SPI_DRIVER
 	bool "SPI character driver"
 	default n

include/nuttx/spi/spi.h

@@ -225,6 +225,10 @@
    *          condition. (see spi_exchange)
    *   Bit 4: HWFEAT_LSBFIRST
    *          Data transferred LSB first (default is MSB first)
+   *   Bit 5: Turn deferred trigger mode on or off.  Primarily used for DMA
+   *          mode.  If a transfer is deferred then the DMA will not actually
+   *          be triggered until a subsequent call to SPI_TRIGGER to set it
+   *          off.
    */
 
 #  ifdef CONFIG_SPI_CRCGENERATION
@@ -243,6 +247,10 @@
 #    define HWFEAT_LSBFIRST                          (1 << 4)
 #  endif
 
+#  ifdef CONFIG_SPI_TRIGGER
+#    define HWFEAT_TRIGGER                           (1 << 5)
+#  endif
+
 #else
   /* Any attempt to select hardware features with CONFIG_SPI_HWFEATURES
    * deselected will return an -ENOSYS error.
@@ -420,6 +428,25 @@
 #define SPI_REGISTERCALLBACK(d,c,a) \
   ((d)->ops->registercallback ? (d)->ops->registercallback(d,c,a) : -ENOSYS)
 
+/****************************************************************************
+ * Name: SPI_TRIGGER
+ *
+ * Description:
+ *   Trigger a previously configured DMA transfer.
+ *
+ * Input Parameters:
+ *   dev      - Device-specific state data
+ *
+ * Returned Value:
+ *   OK       - Trigger was fired
+ *   -ENOSYS  - Trigger not fired due to lack of DMA or low level support
+ *   -EIO     - Trigger not fired because not previously primed
+ *
+ ****************************************************************************/
+
+#  define SPI_TRIGGER(d) \
+  (((d)->ops->trigger) ? ((d)->ops->trigger(d)) : -ENOSYS)
+
 /* SPI Device Macros ********************************************************/
 
 /* This builds a SPI devid from its type and index */
@@ -549,6 +576,9 @@ struct spi_ops_s
                   FAR const void *buffer, size_t nwords);
   CODE void     (*recvblock)(FAR struct spi_dev_s *dev, FAR void *buffer,
                   size_t nwords);
+#endif
+#ifdef CONFIG_SPI_TRIGGER
+  CODE int      (*trigger)(FAR struct spi_dev_s *dev);
 #endif
   CODE int      (*registercallback)(FAR struct spi_dev_s *dev,
                   spi_mediachange_t callback, void *arg);