FAILED: patch "[PATCH] MIPS: Reinstate platform `__div64_32' handler" failed to apply to 4.4-stable tree

The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From c49f71f60754acbff37505e1d16ca796bf8a8140 Mon Sep 17 00:00:00 2001
From: "Maciej W. Rozycki" <[email protected]>
Date: Tue, 20 Apr 2021 04:50:40 +0200
Subject: [PATCH] MIPS: Reinstate platform `__div64_32' handler

Our current MIPS platform __div64_32' handler is inactive, because it is incorrectly only enabled for 64-bit configurations, for which generic do_div' code does not call it anyway.

The handler is not suitable for being called from there though as it only calculates 32 bits of the quotient under the assumption the 64-bit divident has been suitably reduced. Code for such reduction used to be there, however it has been incorrectly removed with commit c21004cd5b4c ("MIPS: Rewrite <asm/div64.h> to work with gcc 4.4.0."), which should have only updated an obsoleted constraint for an inline asm involving $hi and $lo register outputs, while possibly wiring the original MIPS variant of the do_div' macro as __div64_32' handler for the generic `do_div' implementation

Correct the handler as follows then:

- Revert most of the commit referred, however retaining the current formatting, except for the final two instructions of the inline asm sequence, which the original commit missed. Omit the original 64-bit parts though.

- Rename the original do_div' macro to __div64_32'. Use the combined x' constraint referring to the MD accumulator as a whole, replacing the original individual h' and l' constraints used for $hi and $lo registers respectively, of which h' has been obsoleted with GCC 4.4. Update surrounding code accordingly.

We have since removed support for GCC versions before 4.9, so no need for a special arrangement here; GCC has supported the `x' constraint since forever anyway, or at least going back to 1991.

- Rename the __base' local variable in __div64_32' to __radix' to avoid a conflict with a local variable in do_div'.

- Actually enable this code for 32-bit rather than 64-bit configurations by qualifying it with BITS_PER_LONG being 32 instead of 64. Include <asm/bitsperlong.h> for this macro rather than <linux/types.h> as we don't need anything else.

- Finally include <asm-generic/div64.h> last rather than first.

This has passed correctness verification with test_div64 and reduced the module's average execution time down to 1.0668s and 0.2629s from 2.1529s and 0.5647s respectively for an R3400 CPU @40MHz and a 5Kc CPU @160MHz. For a reference 64-bit `do_div' code where we have the DDIVU instruction available to do the whole calculation right away averages at 0.0660s for the latter CPU.

index dc5ea5736440..b252300e299d 100644
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2000, 2004  Maciej W. Rozycki
+ * Copyright (C) 2000, 2004, 2021  Maciej W. Rozycki
  * Copyright (C) 2003, 07 Ralf Baechle ([email protected])
  *
  * This file is subject to the terms and conditions of the GNU General Public

@@ -9,25 +9,18 @@
 #ifndef __ASM_DIV64_H
 #define __ASM_DIV64_H
 
-#include <asm-generic/div64.h>
-
-#if BITS_PER_LONG == 64
+#include <asm/bitsperlong.h>
 
-#include <linux/types.h>
+#if BITS_PER_LONG == 32
 
 /*
  * No traps on overflows for any of these...
  */
 
-#define __div64_32(n, base)						\
-({									\
+#define do_div64_32(res, high, low, base) ({				\
 	unsigned long __cf, __tmp, __tmp2, __i;				\
 	unsigned long __quot32, __mod32;				\
-	unsigned long __high, __low;					\
-	unsigned long long __n;						\
 									\
-	__high = *__n >> 32;						\
-	__low = __n;							\
 	__asm__(							\
 	"	.set	push					\n"	\
 	"	.set	noat					\n"	\

@@ -51,18 +44,50 @@
 	"	subu	%0, %0, %z6				\n"	\
 	"	addiu	%2, %2, 1				\n"	\
 	"3:							\n"	\
-	"	bnez	%4, 0b\n\t"					\
-	"	 srl	%5, %1, 0x1f\n\t"				\
+	"	bnez	%4, 0b					\n"	\
+	"	 srl	%5, %1, 0x1f				\n"	\
 	"	.set	pop"						\
 	: "=&r" (__mod32), "=&r" (__tmp),				\
 	  "=&r" (__quot32), "=&r" (__cf),				\
 	  "=&r" (__i), "=&r" (__tmp2)					\
-	: "Jr" (base), "0" (__high), "1" (__low));			\
+	: "Jr" (base), "0" (high), "1" (low));				\
 									\
-	(__n) = __quot32;						\
+	(res) = __quot32;						\
 	__mod32;							\
 })
 
-#endif /* BITS_PER_LONG == 64 */
+#define __div64_32(n, base) ({						\
+	unsigned long __upper, __low, __high, __radix;			\
+	unsigned long long __modquot;					\
+	unsigned long long __quot;					\
+	unsigned long long __div;					\
+	unsigned long __mod;						\
+									\
+	__div = (*n);							\
+	__radix = (base);						\
+									\
+	__high = __div >> 32;						\
+	__low = __div;							\
+	__upper = __high;						\
+									\
+	if (__high) {							\
+		__asm__("divu	$0, %z1, %z2"				\
+		: "=x" (__modquot)					\
+		: "Jr" (__high), "Jr" (__radix));			\
+		__upper = __modquot >> 32;				\
+		__high = __modquot;					\
+	}								\
+									\
+	__mod = do_div64_32(__low, __upper, __low, __radix);		\
+									\
+	__quot = __high;						\
+	__quot = __quot << 32 | __low;					\
+	(*n) = __quot;							\
+	__mod;								\
+})
+
+#endif /* BITS_PER_LONG == 32 */
+
+#include <asm-generic/div64.h>
 
 #endif /* __ASM_DIV64_H */