drivers/rpmsg_port_spi_slave: add getrecvbuf callback for zero-copy receive

Add a new getrecvbuf callback to the SPI slave device operations
that allows the slave device to provide a pre-allocated receive
buffer directly to the controller. This enables zero-copy data
transfer by allowing the controller to receive data directly into
the device's buffer instead of copying.

Changes:
- Add SPIS_DEV_GETRECVBUF macro and getrecvbuf callback to
  spi_slave_devops_s structure in include/nuttx/spi/slave.h
- Implement getrecvbuf in rpmsg_port_spi_slave driver
- Update getdata to return 0 as it's no longer used for this path

Signed-off-by: liaoao <liaoao@xiaomi.com>

drivers/rpmsg/rpmsg_port_spi_slave.c

@@ -146,6 +146,9 @@ static size_t rpmsg_port_spi_slave_receive(FAR struct spi_slave_dev_s *dev,
                                            size_t nwords);
 static void rpmsg_port_spi_slave_notify(FAR struct spi_slave_dev_s *dev,
                                         spi_slave_state_t state);
+static size_t
+rpmsg_port_spi_slave_getrecvbuf(FAR struct spi_slave_dev_s *dev,
+                                FAR void **buffer);
 
 /****************************************************************************
  * Private Data
@@ -165,6 +168,7 @@ static const struct spi_slave_devops_s g_rpmsg_port_spi_slave_ops =
   rpmsg_port_spi_slave_getdata,            /* getdata */
   rpmsg_port_spi_slave_receive,            /* receive */
   rpmsg_port_spi_slave_notify,             /* notify */
+  rpmsg_port_spi_slave_getrecvbuf,         /* getrecvbuf */
 };
 
 /****************************************************************************
@@ -359,11 +363,22 @@ static void rpmsg_port_spi_slave_cmddata(FAR struct spi_slave_dev_s *dev,
 
 static size_t rpmsg_port_spi_slave_getdata(FAR struct spi_slave_dev_s *dev,
                                            FAR const void **data)
+{
+  return 0;
+}
+
+/****************************************************************************
+ * Name: rpmsg_port_spi_slave_getrecvbuf
+ ****************************************************************************/
+
+static size_t
+rpmsg_port_spi_slave_getrecvbuf(FAR struct spi_slave_dev_s *dev,
+                                FAR void **buffer)
 {
   FAR struct rpmsg_port_spi_s *rpspi =
     container_of(dev, struct rpmsg_port_spi_s, spislv);
 
-  *data = rpspi->rxhdr;
+  *buffer = rpspi->rxhdr;
   return RPMSG_PORT_SPI_BYTES2WORDS(rpspi, rpspi->port.rxq.len);
 }
 

include/nuttx/spi/slave.h

@@ -266,6 +266,30 @@
 
 #define SPIS_DEV_GETDATA(d,v)  ((d)->ops->getdata(d,v))
 
+/****************************************************************************
+ * Name: SPIS_DEV_GETRECVBUF
+ *
+ * Description:
+ *   This is a SPI device callback should be called when the device would
+ *   like to do a nocopy transfer though the device. When the buffer pointer
+ *   controller get is not NULL, it will transfer the data from enqueue
+ *   directly.
+ *
+ * Input Parameters:
+ *   dev  - SPI Slave device interface instance
+ *   buffer - Pointer to the receive buffer pointer to be shifted in.
+ *
+ * Returned Value:
+ *   The size of data units can be received from this exchange.
+ *
+ * Assumptions:
+ *   May be called from an interrupt handler and the response is usually
+ *   time-critical.
+ *
+ ****************************************************************************/
+
+#define SPIS_DEV_GETRECVBUF(d,b)  ((d)->ops->getrecvbuf(d,b))
+
 /****************************************************************************
  * Name: SPIS_DEV_RECEIVE
  *
@@ -544,6 +568,8 @@ struct spi_slave_devops_s
                            FAR const void *data, size_t nwords);
   CODE void     (*notify)(FAR struct spi_slave_dev_s *sdev,
                           spi_slave_state_t state);
+  CODE size_t   (*getrecvbuf)(FAR struct spi_slave_dev_s *sdev,
+                              FAR void **buffer);
 };
 
 /* SPI slave device private data. This structure only defines the initial