spi: dw: Add deferred DMA-channels setup support

Currently if the source DMA device isn't ready to provide the channels
capable of the SPI DMA transfers, the DW SSI controller will be registered
with no DMA support. It isn't right since all what the driver needs to do
is to postpone the probe procedure until the DMA device is ready. Let's
fix that in the framework of the DWC SSI generic DMA implementation. First
we need to use the dma_request_chan() method instead of the
dma_request_slave_channel() function, because the later one is deprecated
and most importantly doesn't return the failure cause but the
NULL-pointer. Second we need to stop the DW SSI controller probe procedure
if the -EPROBE_DEFER error is returned on the DMA initialization. The
procedure will resume later when the channels are ready to be requested.

Signed-off-by: Serge Semin <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-dw-core.c

···
 
 	if (dws->dma_ops && dws->dma_ops->dma_init) {
 		ret = dws->dma_ops->dma_init(dev, dws);
-		if (ret) {
+		if (ret == -EPROBE_DEFER) {
+			goto err_free_irq;
+		} else if (ret) {
 			dev_warn(dev, "DMA init failed\n");
 		} else {
 			master->can_dma = dws->dma_ops->can_dma;
···
 	if (dws->dma_ops && dws->dma_ops->dma_exit)
 		dws->dma_ops->dma_exit(dws);
 	dw_spi_enable_chip(dws, 0);
+err_free_irq:
 	free_irq(dws->irq, master);
 err_free_master:
 	spi_controller_put(master);

drivers/spi/spi-dw-dma.c

···
 
 static int dw_spi_dma_init_generic(struct device *dev, struct dw_spi *dws)
 {
-	dws->rxchan = dma_request_slave_channel(dev, "rx");
-	if (!dws->rxchan)
-		return -ENODEV;
+	int ret;
 
-	dws->txchan = dma_request_slave_channel(dev, "tx");
-	if (!dws->txchan) {
-		dma_release_channel(dws->rxchan);
+	dws->rxchan = dma_request_chan(dev, "rx");
+	if (IS_ERR(dws->rxchan)) {
+		ret = PTR_ERR(dws->rxchan);
 		dws->rxchan = NULL;
-		return -ENODEV;
+		goto err_exit;
+	}
+
+	dws->txchan = dma_request_chan(dev, "tx");
+	if (IS_ERR(dws->txchan)) {
+		ret = PTR_ERR(dws->txchan);
+		dws->txchan = NULL;
+		goto free_rxchan;
 	}
 
 	dws->master->dma_rx = dws->rxchan;
···
 	dw_spi_dma_sg_burst_init(dws);
 
 	return 0;
+
+free_rxchan:
+	dma_release_channel(dws->rxchan);
+	dws->rxchan = NULL;
+err_exit:
+	return ret;
 }
 
 static void dw_spi_dma_exit(struct dw_spi *dws)