From 6544c84faa84d0263a19f5c32d9224bfb13b9a65 Mon Sep 17 00:00:00 2001
From: Alan Cox <alan@linux.intel.com>
Date: Fri, 13 Feb 2015 17:05:57 +0000
Subject: [PATCH] zx128: fix banking returns through common and discard

With this little gem fixed we can now get all the way through the IDE probe
in banked code and to the bootdev prompt.
---
 Kernel/platform-zx128/zx128.s | 24 ++++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/Kernel/platform-zx128/zx128.s b/Kernel/platform-zx128/zx128.s
index 0bcbb580..26a54773 100644
--- a/Kernel/platform-zx128/zx128.s
+++ b/Kernel/platform-zx128/zx128.s
@@ -281,13 +281,17 @@ bankina0:
 	ld d, (hl)
 	inc hl
 	push hl		   ; Restore corrected return pointer
+	ld bc, (current_map)	; get current bank into B
 	call switch_bank   ; Move to new bank
-	ex de, hl
-	call callhl	   ; can't optimise - we need the stack depth right
-	ret
-callhl:	jp (hl)		   ; calls from bank 0 are different to the others
-			   ; we started in common so we don't need to map
-			   ; the old state back
+	; figure out which bank to map on the return path
+	ld a, c
+	or a
+	jr z, __retmap1
+	dec a
+	jr z, __retmap2
+	jr __retmap3
+
+callhl:	jp (hl)
 __bank_0_2:
 	ld a, #1	   ; logical 2 -> physical 1
 	jr bankina0
@@ -305,6 +309,7 @@ bankina1:
 	inc hl
 	push hl		   ; Restore corrected return pointer
 	call switch_bank   ; Move to new bank
+__retmap1:
 	ex de, hl
 	call callhl	   ; call the function
 	xor a		   ; return to bank 1 (physical 0)
@@ -323,6 +328,7 @@ bankina2:
 	inc hl
 	push hl		   ; Restore corrected return pointer
 	call switch_bank   ; Move to new bank
+__retmap2:
 	ex de, hl
 	call callhl	   ; call the function
 	ld a, #1	   ; return to bank 2
@@ -340,6 +346,7 @@ bankina3:
 	inc hl
 	push hl		   ; Restore corrected return pointer
 	call switch_bank   ; Move to new bank
+__retmap3:
 	ex de, hl
 	call callhl	   ; call the function
 	ld a, #7	   ; return to bank 0
@@ -352,6 +359,11 @@ __bank_3_2:
 ;
 ;	Stubs from common are the easy case and use HL
 ;
+;	FIXME: if we ever stub a function that is in discard/common and
+;	which calls into code that bank switches then returns this will
+;	break. If that happens then these will need munging into the
+;	method used in __bank_0_x (ick)
+;
 __stub_0_1:
 	xor a
 	call switch_bank
-- 
2.34.1