bcm2835-dma: Fixes for dma_abort #5482
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This seems to behave as desired for HDMI audio and SPI display. |
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There is a problem with the current abort scheme when dma is blocked on a DREQ which prevents halting. This is triggered by SPI driver which aborts dma in this state and so leads to a halt timeout. Discussion with Broadcom suggests the sequence: CS.ACTIVE=0 while (CS.OUTSTANDING_TRANSACTIONS == 0) wait() DEBUG.RESET=1 should be safe on a dma40 channel. Unfortunately the non-dma40 channels don't have OUTSTANDING_TRANSACTIONS, so we need a more complicated scheme. We attempt to abort the channel, which will work if there is no blocked DREQ. It it times out, we can assume there is no AXI transfer in progress and reset anyway. The length of the timeout is observed at ~20us. Signed-off-by: Dom Cobley <[email protected]>
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Updated to do something plausible for non-dma40 case. |
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@pelwell any comments? |
pelwell
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May 30, 2023
| @@ -245,6 +245,7 @@ struct bcm2835_desc { | |||
| #define BCM2711_DMA40_ERR BIT(10) | |||
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Can we have the BCM2711_DMA40_PROT bits here?
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Added commit to move PROT bits definition.
Fixes: 654368f ("bcm2835-dma: Need to keep PROT bits set in CS on 40bit controller") Signed-off-by: Dom Cobley <[email protected]>
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See: raspberrypi/linux#5482 kernel: Fix I2C issues for DSI touch and V3 camera See: raspberrypi/linux#5479 kernel: pps: Compatibility hack should be X86-specific See: raspberrypi/linux#5478
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See: raspberrypi/linux#5482 kernel: Fix I2C issues for DSI touch and V3 camera See: raspberrypi/linux#5479 kernel: pps: Compatibility hack should be X86-specific See: raspberrypi/linux#5478
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There is a problem with the current abort scheme
when dma is blocked on a DREQ which prevents halting.
This is triggered by SPI driver which aborts dma
in this state and so leads to a halt timeout.
Discussion with Broadcom suggests the sequence:
should be safe on a dma40 channel.
Unfortunately the non-dma40 channels don't have
OUTSTANDING_TRANSACTIONS, only WAITING_FOR_OUTSTANDING_WRITES which doesn't consider reads.