powerpc/8xx: Move PPC_PIN_TLB options into 8xx Kconfig

PPC_PIN_TLB options are dedicated to the 8xx, move them into
the 8xx Kconfig.

While we are at it, add some text to explain what it does.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/1ece39fac6312e1d14e6a67b3f9d9f9f91990a7b.1589866984.git.christophe.leroy@csgroup.eu

arch/powerpc/Kconfig

@@ -1227,26 +1227,6 @@ config TASK_SIZE
 	hex "Size of user task space" if TASK_SIZE_BOOL
 	default "0x80000000" if PPC_8xx
 	default "0xc0000000"
-
-config PIN_TLB
-	bool "Pinned Kernel TLBs (860 ONLY)"
-	depends on ADVANCED_OPTIONS && PPC_8xx && \
-		   !DEBUG_PAGEALLOC && !STRICT_KERNEL_RWX
-
-config PIN_TLB_DATA
-	bool "Pinned TLB for DATA"
-	depends on PIN_TLB
-	default y
-
-config PIN_TLB_IMMR
-	bool "Pinned TLB for IMMR"
-	depends on PIN_TLB || PPC_EARLY_DEBUG_CPM
-	default y
-
-config PIN_TLB_TEXT
-	bool "Pinned TLB for TEXT"
-	depends on PIN_TLB
-	default y
 endmenu
 
 if PPC64

arch/powerpc/platforms/8xx/Kconfig

@@ -162,4 +162,45 @@ config UCODE_PATCH
 	default y
 	depends on !NO_UCODE_PATCH
 
+menu "8xx advanced setup"
+	depends on PPC_8xx
+
+config PIN_TLB
+	bool "Pinned Kernel TLBs"
+	depends on ADVANCED_OPTIONS && !DEBUG_PAGEALLOC && !STRICT_KERNEL_RWX
+	help
+	  On the 8xx, we have 32 instruction TLBs and 32 data TLBs. In each
+	  table 4 TLBs can be pinned.
+
+	  It reduces the amount of usable TLBs to 28 (ie by 12%). That's the
+	  reason why we make it selectable.
+
+	  This option does nothing, it just activate the selection of what
+	  to pin.
+
+config PIN_TLB_DATA
+	bool "Pinned TLB for DATA"
+	depends on PIN_TLB
+	default y
+	help
+	  This pins the first 32 Mbytes of memory with 8M pages.
+
+config PIN_TLB_IMMR
+	bool "Pinned TLB for IMMR"
+	depends on PIN_TLB || PPC_EARLY_DEBUG_CPM
+	default y
+	help
+	  This pins the IMMR area with a 512kbytes page. In case
+	  CONFIG_PIN_TLB_DATA is also selected, it will reduce
+	  CONFIG_PIN_TLB_DATA to 24 Mbytes.
+
+config PIN_TLB_TEXT
+	bool "Pinned TLB for TEXT"
+	depends on PIN_TLB
+	default y
+	help
+	  This pins kernel text with 8M pages.
+
+endmenu
+
 endmenu