raspi: add dma.resource (BCM2835 DMA channel allocator)#809
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Add a resource (modelled on mbox.resource) that owns DMA channel allocation and DMA_ENABLE_REG, replacing the hardcoded channels and unlocked enable-register RMWs in the in-tree users. DMAAllocChannel and DMAFreeChannel hand out channels. DMACHF_TDMODE reserves a full 2D engine and DMACHF_IRQ adds completion-IRQ wait via DMAWaitChannel. Migrates sdcard, RPiPWM and RPiHDMI. The shared control-block layout and bus-address alias move to <hardware/bcm2708_dma.h>.
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Introduces
dma.resourcefor the BCM2835/2836 — a small resource (modelledafter
mbox.resource) that owns DMA channel allocation and the globalDMA_ENABLE_REG. Until now each DMA user hardcoded a channel number and didits own unlocked read-modify-write on the shared enable register, which races
and leaves the firmware-owned channel knowledge scattered across drivers.
Migrates the following off their hardcoded channels:
sdcard(SDHOST controller)RPiPWMandRPiHDMIAHI driversdma.resourceis added to the raspi kickstart packaging.