spi: rspi: Handle dmaengine_prep_slave_sg() failures gracefully

As typically a shmobile SoC has less DMA channels than devices that can use
DMA, we may want to prioritize access to the DMA channels in the future.
This means that dmaengine_prep_slave_sg() may start failing arbitrarily.

Handle dmaengine_prep_slave_sg() failures gracefully by falling back to
PIO.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mark Brown <broonie@linaro.org>

1 files changed, 22 insertions, 8 deletions

diff --git a/drivers/spi/spi-rspi.c b/drivers/spi/spi-rspi.c
index 38fd938d6360..c850dfdfa9e3 100644
--- a/drivers/spi/spi-rspi.c
+++ b/drivers/spi/spi-rspi.c
@@ -477,7 +477,7 @@ static int rspi_dma_transfer(struct rspi_data *rspi, struct sg_table *tx,
                                         tx->sgl, tx->nents, DMA_TO_DEVICE,
                                         DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
                 if (!desc_tx)
-                        return -EIO;
+                        goto no_dma;
 
                 irq_mask |= SPCR_SPTIE;
         }
@@ -486,7 +486,7 @@ static int rspi_dma_transfer(struct rspi_data *rspi, struct sg_table *tx,
                                         rx->sgl, rx->nents, DMA_FROM_DEVICE,
                                         DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
                 if (!desc_rx)
-                        return -EIO;
+                        goto no_dma;
 
                 irq_mask |= SPCR_SPRIE;
         }
@@ -540,6 +540,12 @@ static int rspi_dma_transfer(struct rspi_data *rspi, struct sg_table *tx,
                 enable_irq(rspi->rx_irq);
 
         return ret;
+
+no_dma:
+        pr_warn_once("%s %s: DMA not available, falling back to PIO\n",
+                     dev_driver_string(&rspi->master->dev),
+                     dev_name(&rspi->master->dev));
+        return -EAGAIN;
 }
 
 static void rspi_receive_init(const struct rspi_data *rspi)
@@ -593,8 +599,10 @@ static int rspi_common_transfer(struct rspi_data *rspi,
 
         if (rspi->master->can_dma && __rspi_can_dma(rspi, xfer)) {
                 /* rx_buf can be NULL on RSPI on SH in TX-only Mode */
-                return rspi_dma_transfer(rspi, &xfer->tx_sg,
-                                         xfer->rx_buf ? &xfer->rx_sg : NULL);
+                ret = rspi_dma_transfer(rspi, &xfer->tx_sg,
+                                        xfer->rx_buf ? &xfer->rx_sg : NULL);
+                if (ret != -EAGAIN)
+                        return ret;
         }
 
         ret = rspi_pio_transfer(rspi, xfer->tx_buf, xfer->rx_buf, xfer->len);
@@ -648,8 +656,11 @@ static int qspi_transfer_out(struct rspi_data *rspi, struct spi_transfer *xfer)
 {
         int ret;
 
-        if (rspi->master->can_dma && __rspi_can_dma(rspi, xfer))
-                return rspi_dma_transfer(rspi, &xfer->tx_sg, NULL);
+        if (rspi->master->can_dma && __rspi_can_dma(rspi, xfer)) {
+                ret = rspi_dma_transfer(rspi, &xfer->tx_sg, NULL);
+                if (ret != -EAGAIN)
+                        return ret;
+        }
 
         ret = rspi_pio_transfer(rspi, xfer->tx_buf, NULL, xfer->len);
         if (ret < 0)
@@ -663,8 +674,11 @@ static int qspi_transfer_out(struct rspi_data *rspi, struct spi_transfer *xfer)
 
 static int qspi_transfer_in(struct rspi_data *rspi, struct spi_transfer *xfer)
 {
-        if (rspi->master->can_dma && __rspi_can_dma(rspi, xfer))
-                return rspi_dma_transfer(rspi, NULL, &xfer->rx_sg);
+        if (rspi->master->can_dma && __rspi_can_dma(rspi, xfer)) {
+                int ret = rspi_dma_transfer(rspi, NULL, &xfer->rx_sg);
+                if (ret != -EAGAIN)
+                        return ret;
+        }
 
         return rspi_pio_transfer(rspi, NULL, xfer->rx_buf, xfer->len);
 }