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init: heuristics for DMA buffer allocations

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If a child is allowed to constrain physical memory allocations but left
the 'phys_start' and 'phys_size' session arguments blank, init applies
builtin constraints for allocating DMA buffers.

The only component that makes use of the physical-memory constraint
feature is the platform driver. Since the built-in heuristics are
applied to the platform driver's environment RAM session, all
allocations performed by the platform driver satisfy the DMA
constraints.

To justify building-in these heuristics into init as opposed to
supplying the values as configuration arguments, the values differ
between 32 and 64 bit. The configuration approach would raise the need
to differentiate init configurations for both cases, which are
completely identical otherwise.

Issue #2407
This commit is contained in:
Norman Feske 2017-05-09 16:43:49 +02:00 committed by Christian Helmuth
parent 420b66a1f0
commit 3fc2a798b2
1 changed files with 22 additions and 3 deletions
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25
repos/os/src/init/child.cc
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@ -572,9 +572,28 @@ void Init::Child::filter_session_args(Service::Name const &service,
* Remove phys_start and phys_size RAM-session arguments unless
* explicitly permitted by the child configuration.
*/
if (service == "RAM" && !_constrain_phys) {
Arg_string::remove_arg(args, "phys_start");
Arg_string::remove_arg(args, "phys_size");
if (service == "RAM") {
/*
* If the child is allowed to constrain physical memory allocations,
* pass the child-provided constraints as session arguments to core.
* If no constraints are specified, we apply the constraints for
* allocating DMA memory (as the only use case for the constrain-phys
* mechanism).
*/
if (_constrain_phys) {
addr_t start = 0;
addr_t size = (sizeof(long) == 4) ? 0xc0000000UL : 0x100000000UL;
Arg_string::find_arg(args, "phys_start").ulong_value(start);
Arg_string::find_arg(args, "phys_size") .ulong_value(size);
Arg_string::set_arg(args, args_len, "phys_start", String<32>(Hex(start)).string());
Arg_string::set_arg(args, args_len, "phys_size", String<32>(Hex(size)) .string());
} else {
Arg_string::remove_arg(args, "phys_start");
Arg_string::remove_arg(args, "phys_size");
}
}
}