spi: dw: Wait for idle after TX #6646
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Updated with a more complete solution, which needs retesting in its current form. Restructuring |
If this is a DMA transfer, and if there is no simultaneous RX transfer, wait for the interface to go idle before reporting that TX is done. Link: https://forums.raspberrypi.com/viewtopic.php?t=383027 Signed-off-by: Phil Elwell <[email protected]>
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The maximum time between the tx_busy check passing (==txfifo empty) and the SR_BUSY check passing is one complete wordsize. I think the cpu_relax() should be another invocation of spi_delay_exec() but with delay.value set to just n_bytes * BITS_PER_BYTE - in the case where you have a slow SPI SCLK and a large wordsize, the driver could be spinning for a nontrivial amount of time. |
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See: raspberrypi/linux#6636 kernel: misc: rp1-pio: SM_CONFIG_XFER32 = larger DMA bufs See: raspberrypi/linux#6640 kernel: Handle probe dependencies and hard errors better See: raspberrypi/linux#6645 kernel: spi: dw: Wait for idle after TX See: raspberrypi/linux#6646 See: raspberrypi/linux#6649
popcornmix
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See: raspberrypi/linux#6636 kernel: misc: rp1-pio: SM_CONFIG_XFER32 = larger DMA bufs See: raspberrypi/linux#6640 kernel: Handle probe dependencies and hard errors better See: raspberrypi/linux#6645 kernel: spi: dw: Wait for idle after TX See: raspberrypi/linux#6646 See: raspberrypi/linux#6649
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This is probably part 1 of a fix for TX only transfers. Part 2 is likely to change dw_spi_dma_transfer to not call dw_spi_wait_tx_done in the event that there is an RX buffer.
Link: https://forums.raspberrypi.com/viewtopic.php?t=383027