On Tue, Oct 07, 2014 at 09:38:47PM -0700, Ray Jui wrote: > The PL022 SPI driver maps the DMA RX buffer before the DMA TX buffer. In > most cases, the sequence of the mapping does not matter. But in cases > where TX and RX happen to use the same buffer, e.g., spidev, it causes > the cached TX data not written to memory, because the same memory has > been marked invalid when dma_map_sg on the RX buffer is called This seems like it is a bug in spidev, using the same buffer simultaneously for both directions isn't something I'd think would be expected to work reliably unless it was explicitly mapped as bidirectional.
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