spi: spi-fsl-dspi: Stub out DMA functions

In a later commit we'll use dma_alloc_noncoherent() which isn't
stubbed out for builds without CONFIG_DMA_ENGINE and results in the
following build error:

  spi-fsl-dspi.c:(.text+0x644): undefined reference to `dma_free_pages'
  m68k-linux-ld: spi-fsl-dspi.c:(.text+0x67a): undefined reference to `dma_free_pages'

To continue to support devices that only need XSPI mode and so that
randconfig builds work, stub out DMA functionality in the DSPI driver.

Although older parts of the DMA API have their own stubs, it's
intentional that newer parts don't follow the same pattern. Therefore
individual drivers should not compile in calls unless CONFIG_DMA_ENGINE
is set.

Link: https://lore.kernel.org/oe-kbuild-all/202506160036.t9VDxF6p-lkp@intel.com/
Signed-off-by: James Clark <james.clark@linaro.org>
Reported-by: kernel test robot <lkp@intel.com>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Message-ID: <20250902-james-nxp-spi-dma-v6-3-f7aa2c5e56e2@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: james-c-linaro

drivers/spi/spi-fsl-dspi.c

@@ -373,6 +373,8 @@ struct fsl_dspi {
 	void (*dev_to_host)(struct fsl_dspi *dspi, u32 rxdata);
 };
 
+static void dspi_setup_accel(struct fsl_dspi *dspi);
+
 static bool is_s32g_dspi(struct fsl_dspi *data)
 {
 	return data->devtype_data == &devtype_data[S32G] ||
@@ -468,6 +470,16 @@ static u32 dspi_pop_tx(struct fsl_dspi *dspi)
 	return txdata;
 }
 
+/* Push one word to the RX buffer from the POPR register (RX FIFO) */
+static void dspi_push_rx(struct fsl_dspi *dspi, u32 rxdata)
+{
+	if (!dspi->rx)
+		return;
+	dspi->dev_to_host(dspi, rxdata);
+}
+
+#if IS_ENABLED(CONFIG_DMA_ENGINE)
+
 /* Prepare one TX FIFO entry (txdata plus cmd) */
 static u32 dspi_pop_tx_pushr(struct fsl_dspi *dspi)
 {
@@ -481,14 +493,6 @@ static u32 dspi_pop_tx_pushr(struct fsl_dspi *dspi)
 	return cmd << 16 | data;
 }
 
-/* Push one word to the RX buffer from the POPR register (RX FIFO) */
-static void dspi_push_rx(struct fsl_dspi *dspi, u32 rxdata)
-{
-	if (!dspi->rx)
-		return;
-	dspi->dev_to_host(dspi, rxdata);
-}
-
 static void dspi_tx_dma_callback(void *arg)
 {
 	struct fsl_dspi *dspi = arg;
@@ -589,8 +593,6 @@ static int dspi_next_xfer_dma_submit(struct fsl_dspi *dspi)
 	return 0;
 }
 
-static void dspi_setup_accel(struct fsl_dspi *dspi);
-
 static void dspi_dma_xfer(struct fsl_dspi *dspi)
 {
 	struct spi_message *message = dspi->cur_msg;
@@ -722,6 +724,18 @@ static void dspi_release_dma(struct fsl_dspi *dspi)
 		dma_release_channel(dma->chan_rx);
 	}
 }
+#else
+static void dspi_dma_xfer(struct fsl_dspi *dspi)
+{
+	dspi->cur_msg->status = -EINVAL;
+}
+static int dspi_request_dma(struct fsl_dspi *dspi, phys_addr_t phy_addr)
+{
+	dev_err(&dspi->pdev->dev, "DMA support not enabled in kernel\n");
+	return -EINVAL;
+}
+static void dspi_release_dma(struct fsl_dspi *dspi) {}
+#endif
 
 static void hz_to_spi_baud(char *pbr, char *br, int speed_hz,
 			   unsigned long clkrate, bool mtf_enabled)