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[01/11] include/hw/boards.h: Document memory_region_allocate_system_memory()

Message ID 1499438577-7674-2-git-send-email-peter.maydell@linaro.org
State Accepted
Commit 09ad643823dcda0a86eddce1291c28d0ccb09a3b
Headers show
Series Make memory_region_init_ram() and friends handle migration | expand

Commit Message

Peter Maydell July 7, 2017, 2:42 p.m. UTC 
Add a documentation comment for memory_region_allocate_system_memory().

In particular, the reason for this function's existence and the
requirement on board code to call it exactly once are non-obvious.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

---
 include/hw/boards.h | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

-- 
2.7.4

Comments

Paolo Bonzini July 10, 2017, 9:42 a.m. UTC | #1 
On 07/07/2017 16:42, Peter Maydell wrote:
> + * Memory allocated via this function will be backed with the memory

> + * backend the user provided using -mem-path if appropriate


I'd change it to

using "-mem-path" or "-numa node,memdev=...".

Paolo

> ; this

> + * is typically used to cause host huge pages to be used.

> + * This function should therefore be called by a board exactly once,

> + * for the primary or largest RAM area it implements.
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Patch

diff --git a/include/hw/boards.h b/include/hw/boards.h
index 76ce021..1bc5389 100644
--- a/include/hw/boards.h
+++ b/include/hw/boards.h
@@ -9,6 +9,34 @@ 
 #include "qom/object.h"
 #include "qom/cpu.h"
 
+/**
+ * memory_region_allocate_system_memory - Allocate a board's main memory
+ * @mr: the #MemoryRegion to be initialized
+ * @owner: the object that tracks the region's reference count
+ * @name: name of the memory region
+ * @ram_size: size of the region in bytes
+ *
+ * This function allocates the main memory for a board model, and
+ * initializes @mr appropriately. It also arranges for the memory
+ * to be migrated (by calling vmstate_register_ram_global()).
+ *
+ * Memory allocated via this function will be backed with the memory
+ * backend the user provided using -mem-path if appropriate; this
+ * is typically used to cause host huge pages to be used.
+ * This function should therefore be called by a board exactly once,
+ * for the primary or largest RAM area it implements.
+ *
+ * For boards where the major RAM is split into two parts in the memory
+ * map, you can deal with this by calling memory_region_allocate_system_memory()
+ * once to get a MemoryRegion with enough RAM for both parts, and then
+ * creating alias MemoryRegions via memory_region_init_alias() which
+ * alias into different parts of the RAM MemoryRegion and can be mapped
+ * into the memory map in the appropriate places.
+ *
+ * Smaller pieces of memory (display RAM, static RAMs, etc) don't need
+ * to be backed via the -mem-path memory backend and can simply
+ * be created via memory_region_init_ram().
+ */
 void memory_region_allocate_system_memory(MemoryRegion *mr, Object *owner,
                                           const char *name,
                                           uint64_t ram_size);