On 16/01/2021 02:56, Nathan Lynch wrote:
Alexey Kardashevskiy <a...@ozlabs.ru> writes:
On 15/01/2021 09:00, Nathan Lynch wrote:
diff --git a/arch/powerpc/include/asm/rtas.h b/arch/powerpc/include/asm/rtas.h
index 332e1000ca0f..1aa7ab1cbc84 100644
--- a/arch/powerpc/include/asm/rtas.h
+++ b/arch/powerpc/include/asm/rtas.h
@@ -19,8 +19,11 @@
#define RTAS_UNKNOWN_SERVICE (-1)
#define RTAS_INSTANTIATE_MAX (1ULL<<30) /* Don't instantiate rtas at/above
this value */
-/* Buffer size for ppc_rtas system call. */
-#define RTAS_RMOBUF_MAX (64 * 1024)
+/* Work areas shared with RTAS must be 4K, naturally aligned. */
Why exactly 4K and not (for example) PAGE_SIZE?
4K is a platform requirement and isn't related to Linux's configured
page size. See the PAPR specification for RTAS functions such as
ibm,configure-connector, ibm,update-nodes, ibm,update-properties.
Good, since we are documenting things here - add to the comment ("per
PAPR")?
There are other calls with work area parameters where alignment isn't
specified (e.g. ibm,get-system-parameter) but 4KB alignment is a safe
choice for those.
+#define RTAS_WORK_AREA_SIZE 4096
+
+/* Work areas allocated for user space access. */
+#define RTAS_USER_REGION_SIZE (RTAS_WORK_AREA_SIZE * 16)
This is still 64K but no clarity why. There is 16 of something, what
is it?
There are 16 4KB work areas in the region. I can name it
RTAS_NR_USER_WORK_AREAS or similar.
Why 16? PAPR (then add "per PAPR") or we just like 16 ("should be enough")?
--
Alexey
