spi: spi-imx: spi_imx_transfer_one(): check for DMA transfer first

The SPI framework checks for each transfer (with the struct
spi_controller::can_dma callback) whether the driver wants to use DMA
for the transfer. If the driver returns true, the SPI framework will
map the transfer's data to the device, start the actual transfer and
map the data back.

In commit 07e75938 ("spi: spi-imx: add PIO polling support") the
spi-imx driver's spi_imx_transfer_one() function was extended. If the
estimated duration of a transfer does not exceed a configurable
duration, a polling transfer function is used. This check happens
before checking if the driver decided earlier for a DMA transfer.

If spi_imx_can_dma() decided to use a DMA transfer, and the user
configured a big maximum polling duration, a polling transfer will be
used. The DMA unmap after the transfer destroys the transferred data.

To fix this problem check in spi_imx_transfer_one() if the driver
decided for DMA transfer first, then check the limits for a polling
transfer.

Fixes: 07e75938 ("spi: spi-imx: add PIO polling support")
Link: https://lore.kernel.org/all/20221111003032.82371-1-festevam@gmail.comReported-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reported-by: Fabio Estevam <festevam@gmail.com>
Tested-by: Fabio Estevam <festevam@gmail.com>
Cc: David Jander <david@protonic.nl>
Cc: stable@vger.kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
Tested-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Link: https://lore.kernel.org/r/20221116164930.855362-1-mkl@pengutronix.deSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-imx.c

@@ -1606,6 +1606,13 @@ static int spi_imx_transfer_one(struct spi_controller *controller,
 	if (spi_imx->slave_mode)
 		return spi_imx_pio_transfer_slave(spi, transfer);
 
+	/*
+	 * If we decided in spi_imx_can_dma() that we want to do a DMA
+	 * transfer, the SPI transfer has already been mapped, so we
+	 * have to do the DMA transfer here.
+	 */
+	if (spi_imx->usedma)
+		return spi_imx_dma_transfer(spi_imx, transfer);
 	/*
 	 * Calculate the estimated time in us the transfer runs. Find
 	 * the number of Hz per byte per polling limit.
@@ -1617,9 +1624,6 @@ static int spi_imx_transfer_one(struct spi_controller *controller,
 	if (transfer->len < byte_limit)
 		return spi_imx_poll_transfer(spi, transfer);
 
-	if (spi_imx->usedma)
-		return spi_imx_dma_transfer(spi_imx, transfer);
-
 	return spi_imx_pio_transfer(spi, transfer);
 }