projects/ad738x_fmc: add DMA gate to SPI offload trigger #1807
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Add an AND gate to disable the SPI offload trigger when the DMA is full. Before this change, when NUM_OF_SDI=1, the SPI offload would pause in the middle of a SPI message when the DMA got full which confused both the DMA controller and the ADC chip causing data channels to become misalligned in memory. After this change, the trigger is prevented from firing when the DMA is full so the SPI message doesn't even start, avoiding the problems mentioned above. Signed-off-by: David Lechner <dlechner@baylibre.com>
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This is a patch that I have been using locally for quite a while while working on the Linux driver for AD738x. I've also been discussing with @LBFFilho if this is sufficient or if additional fixes are needed, but from a bunch of testing, this seems to be working well.
PR Description
Add an AND gate to disable the SPI offload trigger when the DMA is full.
Before this change, when NUM_OF_SDI=1, the SPI offload would pause in the middle of a SPI message when the DMA got full which confused both the DMA controller and the ADC chip causing data channels to become misalligned in memory.
After this change, the trigger is prevented from firing when the DMA is full so the SPI message doesn't even start, avoiding the problems mentioned above.
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