RE: [PATCH 2/2] powerpc: Make context bits depend on virtual addr size.
From: David Laight <hidden>
Date: 2013-02-13 13:34:57
+#define CONTEXT_BITS 19 +#define USER_ESID_BITS 18 +#define USER_ESID_BITS_1T 6 + +/* + * 256MB segment + * The proto-VSID space has 2^(CONTEX_BITS + USER_ESID_BITS) - 1 =
segments
+ * available for user + kernel mapping. The top 4 contexts are used =
for
+ * kernel mapping. Each segment contains 2^28 bytes. Each + * context maps 2^46 bytes (64TB) so we can support 2^19-1 contexts + * (19 =3D=3D 37 + 28 - 46). + */
I can't help feeling this would be easier to understand if a full 64? 80? bit address was shown with the various bit ranges identified. Given the comment, I'd have expected CONTEXT_BITS to be calculated from three other named constants - rather than being set to 19. David