readme.dmareservedarea

神龙卡开发原代码

Starting with release v1_6_93_16_SONY, RPK allows the user to
compile the kernel module with

$ export REALMAGICHWL_FEATURES="-I... ... ... -DWITH_DMA_RESERVED_AREA=1" 
$ make all

This version does not use pci_alloc/free_consistent() to allocate
DMA buffers but a static allocation strategy, making allocation success
100% certain even on low-memory machines, provided some physical top
ram has been reserved at kernel startup.

In this variation, realmagichwl_kernelland.o now has two mandatory
parameters at insmod:

# insmod realmagichwl_kernelland.o dmareservedarea_physicaladdress=0x...
dmareservedarea_size=...

I assume you are able to compute the physical address of the first byte that
will not be used by Linux.

For instance, if hac/hvc has a physical memory of 128MB, 
kernel usable addresses are [0x0000 0000,0x0800 0000[
After restriction:          [0x0000 0000,0x07f0 0000[ is for Linux
                        and [0x07f0 0000,0x0800 0000[ is for Sigma driver
by telling:

insmod realmagichwl_kernelland.o dmareservedarea_physicaladdress=0x07f00000 
dmareservedarea_size=1048576

Real-life situation is not so easy if your BIOS or NVRAM uses some
high address in physical RAM. You have to inspect carefully this issue
with your montavista-tiger team.

Hopefully the ioremap() call will be rejected if memory areas above
overlap or overflow the actual memory.

Note. There is no way to restrict the quantity of RAM used by a Linux
kernel once the startup has begun, since it will naturally expand to
the complete RAM for kernel code, data, buffers, and file cache.