This API rework eases the access to memory-mapped I/O registers and
interrupts when using the platform driver. It introduces the notions of
- Platform::Device - one device obtained from a platform session
- Platform::Device::Mmio - locally-mapped MMIO registers of a device
- Platform::Device::Irq - interface for receiving device interrupts
The patch touches several drivers. Some drivers would require a
significant structural change to adopt the new API (e.g., net/virtio,
dde_linux drivers, imx gpio). In these cases, the patch adds
compatibility shims meant to be temporary. In other cases (e.g., imx
i2c), the adaptation was simple enough to carry through.
Fixes#4075
This patch extends the 'Platform_session::alloc_dma_buffer' interface
with a 'Cache' argument that corresponds to the argument accepted by
'Ram_allocator::alloc', which is used by the platform driver under the
hood.
Since the x86 platform driver used to be hardwired to allocate DMA
buffers as UNCACHED, I adjusted all drivers by specifying the UNCACHED
argument. Right now, this is needed as a hint for core to steer the
allocation of I/O page tables. Once we eliminate the need for such hints
(by introducing an explicit 'Region_map::attach_dma' operation), we can
revisit the drivers individually because cached DMA buffers should
generally be fine on the x86 architecture.
Issue #2243
