On the Renesas RZ/G2L platform, the RSPI driver falls back to PIO mode
instead of using DMA when the DMA controller driver is built as a module
(CONFIG_RZ_DMAC=m):

    renesas_spi 1004b000.spi: dma_request_slave_channel_compat failed
    renesas_spi 1004b000.spi: DMA not available, using PIO

The driver requests DMA channels through dma_request_slave_channel_compat()
which returns either a valid pointer or NULL and cannot handle
-EPROBE_DEFER. If the DMA controller has not probed yet, the driver falls
back to PIO directly.

Fix this by replacing the dma_request_slave_channel_compat() call with a
regular dma_request_chan() call. dma_request_slave_channel_compat() is
always passed a NULL fn_param in all code paths, so it actually behaves
like a plain dma_request_chan() call.

Fixes: e825b8dd2b36 ("spi: rspi: Add DT support to DMA setup")
Signed-off-by: Ovidiu Panait <ovidiu.panait.rb@renesas.com>
---
 drivers/spi/spi-rspi.c | 49 ++++++++++++++++--------------------------
 1 file changed, 19 insertions(+), 30 deletions(-)

diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c
index 38df676774ee..c61edd1c1353 100644
--- a/drivers/spi/spi-rspi.c
+++ b/drivers/spi/spi-rspi.c
@@ -22,7 +22,6 @@
 #include <linux/of.h>
 #include <linux/pm_runtime.h>
 #include <linux/reset.h>
-#include <linux/sh_dma.h>
 #include <linux/spi/spi.h>
 #include <linux/spinlock.h>
 
@@ -1091,24 +1090,15 @@ static irqreturn_t rspi_irq_tx(int irq, void *_sr)
 
 static struct dma_chan *rspi_request_dma_chan(struct device *dev,
 					      enum dma_transfer_direction dir,
-					      unsigned int id,
 					      dma_addr_t port_addr)
 {
-	dma_cap_mask_t mask;
 	struct dma_chan *chan;
 	struct dma_slave_config cfg;
 	int ret;
 
-	dma_cap_zero(mask);
-	dma_cap_set(DMA_SLAVE, mask);
-
-	chan = dma_request_slave_channel_compat(mask, shdma_chan_filter,
-				(void *)(unsigned long)id, dev,
-				dir == DMA_MEM_TO_DEV ? "tx" : "rx");
-	if (!chan) {
-		dev_warn(dev, "dma_request_slave_channel_compat failed\n");
-		return NULL;
-	}
+	chan = dma_request_chan(dev, dir == DMA_MEM_TO_DEV ? "tx" : "rx");
+	if (IS_ERR(chan))
+		return chan;
 
 	memset(&cfg, 0, sizeof(cfg));
 	cfg.dst_addr = port_addr + RSPI_SPDR;
@@ -1121,7 +1111,7 @@ static struct dma_chan *rspi_request_dma_chan(struct device *dev,
 	if (ret) {
 		dev_warn(dev, "dmaengine_slave_config failed %d\n", ret);
 		dma_release_channel(chan);
-		return NULL;
+		return ERR_PTR(ret);
 	}
 
 	return chan;
@@ -1130,29 +1120,23 @@ static struct dma_chan *rspi_request_dma_chan(struct device *dev,
 static int rspi_request_dma(struct device *dev, struct spi_controller *ctlr,
 			    const struct resource *res)
 {
-	unsigned int dma_tx_id, dma_rx_id;
+	struct dma_chan *chan;
 
-	if (dev->of_node) {
-		/* In the OF case we will get the slave IDs from the DT */
-		dma_tx_id = 0;
-		dma_rx_id = 0;
-	} else {
-		/* The driver assumes no error. */
+	if (!dev->of_node)
 		return 0;
-	}
 
-	ctlr->dma_tx = rspi_request_dma_chan(dev, DMA_MEM_TO_DEV, dma_tx_id,
-					     res->start);
-	if (!ctlr->dma_tx)
-		return -ENODEV;
+	chan = rspi_request_dma_chan(dev, DMA_MEM_TO_DEV, res->start);
+	if (IS_ERR(chan))
+		return PTR_ERR(chan);
+	ctlr->dma_tx = chan;
 
-	ctlr->dma_rx = rspi_request_dma_chan(dev, DMA_DEV_TO_MEM, dma_rx_id,
-					     res->start);
-	if (!ctlr->dma_rx) {
+	chan = rspi_request_dma_chan(dev, DMA_DEV_TO_MEM, res->start);
+	if (IS_ERR(chan)) {
 		dma_release_channel(ctlr->dma_tx);
 		ctlr->dma_tx = NULL;
-		return -ENODEV;
+		return PTR_ERR(chan);
 	}
+	ctlr->dma_rx = chan;
 
 	ctlr->can_dma = rspi_can_dma;
 	dev_info(dev, "DMA available");
@@ -1355,6 +1339,11 @@ static int rspi_probe(struct platform_device *pdev)
 	}
 
 	ret = rspi_request_dma(&pdev->dev, ctlr, res);
+	if (ret == -EPROBE_DEFER) {
+		dev_err_probe(&pdev->dev, ret,
+			      "failed to request DMA channels\n");
+		goto error2;
+	}
 	if (ret < 0)
 		dev_warn(&pdev->dev, "DMA not available, using PIO\n");
 
-- 
2.34.1

Hi Ovidiu,

On Mon, 21 Sept 2026 at 22:00, Ovidiu Panait
<ovidiu.panait.rb@renesas.com> wrote:
> On the Renesas RZ/G2L platform, the RSPI driver falls back to PIO mode
> instead of using DMA when the DMA controller driver is built as a module
> (CONFIG_RZ_DMAC=m):
>
>     renesas_spi 1004b000.spi: dma_request_slave_channel_compat failed
>     renesas_spi 1004b000.spi: DMA not available, using PIO
>
> The driver requests DMA channels through dma_request_slave_channel_compat()
> which returns either a valid pointer or NULL and cannot handle
> -EPROBE_DEFER. If the DMA controller has not probed yet, the driver falls
> back to PIO directly.
>
> Fix this by replacing the dma_request_slave_channel_compat() call with a
> regular dma_request_chan() call. dma_request_slave_channel_compat() is
> always passed a NULL fn_param in all code paths, so it actually behaves
> like a plain dma_request_chan() call.
>
> Fixes: e825b8dd2b36 ("spi: rspi: Add DT support to DMA setup")
> Signed-off-by: Ovidiu Panait <ovidiu.panait.rb@renesas.com>

Thanks for your patch!

> --- a/drivers/spi/spi-rspi.c
> +++ b/drivers/spi/spi-rspi.c
> @@ -1355,6 +1339,11 @@ static int rspi_probe(struct platform_device *pdev)
>         }
>
>         ret = rspi_request_dma(&pdev->dev, ctlr, res);
> +       if (ret == -EPROBE_DEFER) {
> +               dev_err_probe(&pdev->dev, ret,
> +                             "failed to request DMA channels\n");
> +               goto error2;

Doesn't this make the probe fail if the DMA driver is not available
at all?

> +       }
>         if (ret < 0)
>                 dev_warn(&pdev->dev, "DMA not available, using PIO\n");

The driver still falls back to PIO in case of a missing "dmas"
property, right?

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds