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Clarify usage rules for pmap_remap_vm_attr().

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Not a functional change.

MFC with:	r318021
MFC after:	2 weeks
This commit is contained in:
Michal Meloun 2017-05-13 10:00:24 +00:00
parent e5c4c8aa7f
commit f1ec210574
1 changed files with 18 additions and 1 deletions
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19
sys/arm/arm/pmap-v6.c
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@ -500,7 +500,24 @@ pmap_set_tex(void)
/*
* Remap one vm_meattr class to another one. This can be useful as
* workaround for SOC errata, e.g. if devices must be accessed using
* SO memory class.
* SO memory class.
*
* !!! Please note that this function is absolutely last resort thing.
* It should not be used under normal circumstances. !!!
*
* Usage rules:
* - it shall be called after pmap_bootstrap_prepare() and before
* cpu_mp_start() (thus only on boot CPU). In practice, it's expected
* to be called from platform_attach() or platform_late_init().
*
* - if remapping doesn't change caching mode, or until uncached class
* is remapped to any kind of cached one, then no other restriction exists.
*
* - if pmap_remap_vm_attr() changes caching mode, but both (original and
* remapped) remain cached, then caller is resposible for calling
* of dcache_wbinv_poc_all().
*
* - remapping of any kind of cached class to uncached is not permitted.
*/
void
pmap_remap_vm_attr(vm_memattr_t old_attr, vm_memattr_t new_attr)