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 07e759387788 ("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: 07e759387788 ("spi: spi-imx: add PIO polling support")
Link: https://lore.kernel.org/all/[email protected]
Reported-by: Frieder Schrempf <[email protected]>
Reported-by: Fabio Estevam <[email protected]>
Tested-by: Fabio Estevam <[email protected]>
Cc: David Jander <[email protected]>
Cc: [email protected]
Signed-off-by: Marc Kleine-Budde <[email protected]>
Tested-by: Frieder Schrempf <[email protected]>
Reviewed-by: Frieder Schrempf <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Mark Brown <[email protected]>

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