vmo_set_cache_policy - set the caching policy for pages held by a VMO.
#include <magenta/syscalls.h> mx_status_t vmo_set_cache_policy(mx_handle_t handle, uint32_t cache_policy);
vmo_set_cache_policy() sets caching policy for a VMO holding physical memory. Such VMOs are generally only handed to userspace via bus protocol interfaces, so this syscall will typically only be used by drivers dealing with device memory. A handle must have the MX_RIGHT_MAP right for this call to be permitted. Additionally, the VMO must not presently be mapped by any process, and the cache policy must not have been set prior to this call.
cache_policy cache flags to use:
MX_CACHE_POLICY_CACHED - Use hardware caching.
MX_CACHE_POLICY_UNCACHED - Disable caching.
MX_CACHE_POLICY_UNCACHED_DEVICE - Disable cache and treat as device memory. This is architecture dependent and may be equivalent to MX_CACHE_POLICY_UNCACHED on some architectures.
MX_CACHE_POLICY_WRITE_COMBINING - Use write combining. This is architecture dependent and may be equivalent to MX_CACHE_POLICY_UNCACHED.
vmo_set_cache_policy() returns MX_OK on success. In the event of failure, a negative error value is returned.
MX_ERR_ACCESS_DENIED Cache policy has been configured for this VMO already and may not be changed, or handle lacks the MX_RIGHT_MAP right.
MX_ERR_BAD_HANDLE handle is not a valid handle.
MX_ERR_INVALID_ARGS cache_policy contains flags outside of the ones listed above, or cache_policy contains an invalid mix of cache policy flags.
MX_ERR_NOT_SUPPORTED The VMO handle corresponds to is not one holding physical memory.
MX_ERR_BAD_STATE Cache policy cannot be changed because the VMO is presently mapped.
vmo_create, vmo_read, vmo_write, vmo_get_size, vmo_set_size, vmo_op_range.