Improve PIO DMA performance #6994
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If the DMA channel allocation fails, the relevant dma_configs entry should be marked as no longer claimed, otherwise rp1_pio_sm_dma_free will be called with an error number as a DMA channel pointer. Signed-off-by: Phil Elwell <phil@raspberrypi.com>
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Channels 0 and 1 were configured with MSIZE=8, not 16. Those channels will only issue 8-beat bursts in response to a request, so there will be a mismatch in FIFO fill levels vs thresholds. |
The DesignWare AXI DMAC IP can be configured with heterogeneous channel parameters. Allow maximum burst length to be set per-channel by making snps,axi-max-burst-len an array. Signed-off-by: Phil Elwell <phil@raspberrypi.com>
Add a mechanism to allow clients to prefer some DMA channels over others. This is required to allow high-bandwidth clients to request one of the two "heavy" channels, but could also be used to prevent some clients from hogging all channels. Signed-off-by: Phil Elwell <phil@raspberrypi.com>
Give the DMAC property "snps,axi-max-burst-len" a value for each DMA
channel, encoding the fact that channels 1 and 2 are more capable
("heavy").
Signed-off-by: Phil Elwell <phil@raspberrypi.com>
PIO benefits from increased DMA bandwidth when used with DMA channels 0 or 1, because they support longer bursts. Add DMA channel selection attributes to prevent other users from claiming them. Signed-off-by: Phil Elwell <phil@raspberrypi.com>
Improve DMA performance by increasing the burst size to 8. Signed-off-by: Phil Elwell <phil@raspberrypi.com>
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I knew that, on some level. Updated with the 16s changed to 8s, and with the rp1-pio code changes broken out into a separate commit (as it should always have been). |
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The RP1 DMA controller configuration makes channels 1 and 2 more capable than the others. Add a mechanism to reserve those channels for the PIO block. There may be other ways to improve the DMA bandwidth when talking to the PIO block, but this alone more than doubles the throughput.