dmaengine: Add a warning for drivers not using the generic slave caps…

… retrieval

For the slave caps retrieval to be really useful, most drivers need to
implement it.

Hence, we need to be slightly more aggressive, and trigger a warning at
registration time for drivers that don't fill their caps infos in order to
encourage them to implement it.

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

drivers/dma/dmaengine.c

@@ -826,6 +826,9 @@ int dma_async_device_register(struct dma_device *device)
 	BUG_ON(!device->device_issue_pending);
 	BUG_ON(!device->dev);
 
+	WARN(dma_has_cap(DMA_SLAVE, device->cap_mask) && !device->directions,
+	     "this driver doesn't support generic slave capabilities reporting\n");
+
 	/* note: this only matters in the
 	 * CONFIG_ASYNC_TX_ENABLE_CHANNEL_SWITCH=n case
 	 */