spi: davinci: always start transmit DMA
Due to the full duplex nature of the SPI bus, the SPI master on DaVinci needs transmit to be active even if the tranfer is only meant to collect receive data. The current code achieves this by using a temporary zeroed buffer to provide DMA data in case the transfer does not have a transmit buffer provided. However, the transmit DMA is started only if transmit buffer is provided rendering the temporary buffer unused. Instead the code relies on a write to SPIDAT1 register to trigger transmit operation. This however only sends two bytes of data. Fix this by starting transmit DMA always. This changes exposes a bug on DM355 where the CSHOLD bit in SPIDAT1 needs to be written to in between transfers. Handle that by introducing a "cshold_bug" platform data which is set to true for DM355. Signed-off-by: NBrian Niebuhr <bniebuhr@efjohnson.com> Tested-By: NMichael Williamson <michael.williamson@criticallink.com> Signed-off-by: NSekhar Nori <nsekhar@ti.com>
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