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

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2071848
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2122415

commit e85e9e0
Author: Marc Kleine-Budde <mkl@pengutronix.de>
Date: Wed, 16 Nov 2022 17:49:30 +0100

    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 07e7593 ("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: 07e7593 ("spi: spi-imx: add PIO polling support")
    Link: https://lore.kernel.org/all/20221111003032.82371-1-festevam@gmail.com
    Reported-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.de
    Signed-off-by: Mark Brown <broonie@kernel.org>

Signed-off-by: Mark Salter <msalter@redhat.com>

Author: mosalter

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);
 }