[dma] Define a DMA API to allow for non-flat device address spaces

iPXE currently assumes that DMA-capable devices can directly address
physical memory using host addresses.  This assumption fails when
using an IOMMU.

Define an internal DMA API with two implementations: a "flat"
implementation for use in legacy BIOS or other environments in which
flat physical addressing is guaranteed to be used and all allocated
physical addresses are guaranteed to be within a 32-bit address space,
and an "operations-based" implementation for use in UEFI or other
environments in which DMA mapping may require bus-specific handling.

The purpose of the fully inlined "flat" implementation is to allow the
trivial identity DMA mappings to be optimised out at build time,
thereby avoiding an increase in code size for legacy BIOS builds.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/config/defaults/efi.h

@@ -12,6 +12,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define UACCESS_EFI
 #define IOMAP_VIRT
 #define PCIAPI_EFI
+#define DMAAPI_OP
 #define CONSOLE_EFI
 #define TIMER_EFI
 #define UMALLOC_EFI

src/config/defaults/linux.h

@@ -20,6 +20,7 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #define TIME_LINUX
 #define REBOOT_NULL
 #define PCIAPI_LINUX
+#define DMAAPI_FLAT
 
 #define DRIVERS_LINUX
 

src/config/defaults/pcbios.h

@@ -12,6 +12,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define UACCESS_LIBRM
 #define IOAPI_X86
 #define PCIAPI_PCBIOS
+#define DMAAPI_FLAT
 #define TIMER_PCBIOS
 #define CONSOLE_PCBIOS
 #define NAP_PCBIOS