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[PATCH] staging: goldfish: use div64_s64 instead of do_div

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  [PATCH] staging: goldfish: use div64_s64 instead of do_div Arnd Bergmann <arnd@arndb.de> - 2016-02-01 11:40 +0100
    Re: [PATCH] staging: goldfish: use div64_s64 instead of do_div One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2016-02-01 16:00 +0100
      Re: [PATCH] staging: goldfish: use div64_s64 instead of do_div Arnd Bergmann <arnd@arndb.de> - 2016-02-01 17:20 +0100
    Re: [PATCH] staging: goldfish: use div64_s64 instead of do_div One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk> - 2016-02-02 17:40 +0100

#1322975 — [PATCH] staging: goldfish: use div64_s64 instead of do_div

The goldfish nand driver divides a signed 64-bit number (loff_t)
in multiple places using the do_div() function. This has always
been unreliable but now produces a compiler warning (since 4.5-rc1):

goldfish/goldfish_nand.c: In function 'goldfish_nand_erase':
goldfish/goldfish_nand.c:107:91: error: comparison of distinct pointer types lacks a cast [-Werror]
goldfish/goldfish_nand.c: In function 'goldfish_nand_read_oob':
goldfish/goldfish_nand.c:145:91: error: comparison of distinct pointer types lacks a cast [-Werror]

This changes the code to the equivalent div_s64{,_rem} that
works correctly for negative numbers (which we should never
get here).

The warning has shown up on ARM allmodconfig builds after the goldfish
bus driver has become visible on ARM.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: bd2f348db503 ("goldfish: refactor goldfish platform configs")

diff --git a/drivers/staging/goldfish/goldfish_nand.c b/drivers/staging/goldfish/goldfish_nand.c
index f223b3a5a428..76d60eed1490 100644
--- a/drivers/staging/goldfish/goldfish_nand.c
+++ b/drivers/staging/goldfish/goldfish_nand.c
@@ -100,11 +100,11 @@ static int goldfish_nand_erase(struct mtd_info *mtd, struct erase_info *instr)
 {
 	loff_t ofs = instr->addr;
 	u32 len = instr->len;
-	u32 rem;
+	s32 rem;
 
 	if (ofs + len > mtd->size)
 		goto invalid_arg;
-	rem = do_div(ofs, mtd->writesize);
+	ofs = div_s64_rem(ofs, mtd->writesize, &rem);
 	if (rem)
 		goto invalid_arg;
 	ofs *= (mtd->writesize + mtd->oobsize);
@@ -133,7 +133,7 @@ invalid_arg:
 static int goldfish_nand_read_oob(struct mtd_info *mtd, loff_t ofs,
 				  struct mtd_oob_ops *ops)
 {
-	u32 rem;
+	s32 rem;
 
 	if (ofs + ops->len > mtd->size)
 		goto invalid_arg;
@@ -142,7 +142,7 @@ static int goldfish_nand_read_oob(struct mtd_info *mtd, loff_t ofs,
 	if (ops->ooblen + ops->ooboffs > mtd->oobsize)
 		goto invalid_arg;
 
-	rem = do_div(ofs, mtd->writesize);
+	ofs = div_s64_rem(ofs, mtd->writesize, &rem);
 	if (rem)
 		goto invalid_arg;
 	ofs *= (mtd->writesize + mtd->oobsize);
@@ -165,7 +165,7 @@ invalid_arg:
 static int goldfish_nand_write_oob(struct mtd_info *mtd, loff_t ofs,
 				   struct mtd_oob_ops *ops)
 {
-	u32 rem;
+	s32 rem;
 
 	if (ofs + ops->len > mtd->size)
 		goto invalid_arg;
@@ -174,7 +174,7 @@ static int goldfish_nand_write_oob(struct mtd_info *mtd, loff_t ofs,
 	if (ops->ooblen + ops->ooboffs > mtd->oobsize)
 		goto invalid_arg;
 
-	rem = do_div(ofs, mtd->writesize);
+	ofs = div_s64_rem(ofs, mtd->writesize, &rem);
 	if (rem)
 		goto invalid_arg;
 	ofs *= (mtd->writesize + mtd->oobsize);
@@ -197,12 +197,12 @@ invalid_arg:
 static int goldfish_nand_read(struct mtd_info *mtd, loff_t from, size_t len,
 			      size_t *retlen, u_char *buf)
 {
-	u32 rem;
+	s32 rem;
 
 	if (from + len > mtd->size)
 		goto invalid_arg;
 
-	rem = do_div(from, mtd->writesize);
+	from = div_s64_rem(from, mtd->writesize, &rem);
 	if (rem)
 		goto invalid_arg;
 	from *= (mtd->writesize + mtd->oobsize);
@@ -219,12 +219,12 @@ invalid_arg:
 static int goldfish_nand_write(struct mtd_info *mtd, loff_t to, size_t len,
 			       size_t *retlen, const u_char *buf)
 {
-	u32 rem;
+	s32 rem;
 
 	if (to + len > mtd->size)
 		goto invalid_arg;
 
-	rem = do_div(to, mtd->writesize);
+	to = div_s64_rem(to, mtd->writesize, &rem);
 	if (rem)
 		goto invalid_arg;
 	to *= (mtd->writesize + mtd->oobsize);
@@ -240,12 +240,12 @@ invalid_arg:
 
 static int goldfish_nand_block_isbad(struct mtd_info *mtd, loff_t ofs)
 {
-	u32 rem;
+	s32 rem;
 
 	if (ofs >= mtd->size)
 		goto invalid_arg;
 
-	rem = do_div(ofs, mtd->erasesize);
+	ofs = div_s64_rem(ofs, mtd->writesize, &rem);
 	if (rem)
 		goto invalid_arg;
 	ofs *= mtd->erasesize / mtd->writesize;
@@ -261,12 +261,12 @@ invalid_arg:
 
 static int goldfish_nand_block_markbad(struct mtd_info *mtd, loff_t ofs)
 {
-	u32 rem;
+	s32 rem;
 
 	if (ofs >= mtd->size)
 		goto invalid_arg;
 
-	rem = do_div(ofs, mtd->erasesize);
+	ofs = div_s64_rem(ofs, mtd->writesize, &rem);
 	if (rem)
 		goto invalid_arg;
 	ofs *= mtd->erasesize / mtd->writesize;
@@ -321,7 +321,7 @@ static int goldfish_nand_init_device(struct platform_device *pdev,
 	mtd->oobavail = mtd->oobsize;
 	mtd->erasesize = readl(base + NAND_DEV_ERASE_SIZE) /
 			(mtd->writesize + mtd->oobsize) * mtd->writesize;
-	do_div(mtd->size, mtd->writesize + mtd->oobsize);
+	mtd->size = div_s64(mtd->size, mtd->writesize + mtd->oobsize);
 	mtd->size *= mtd->writesize;
 	dev_dbg(&pdev->dev,
 		"goldfish nand dev%d: size %llx, page %d, extra %d, erase %d\n",

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#1323200

On Mon, 01 Feb 2016 11:33 +0100
Arnd Bergmann <arnd@arndb.de> wrote:

> The goldfish nand driver divides a signed 64-bit number (loff_t)
> in multiple places using the do_div() function. This has always
> been unreliable but now produces a compiler warning (since 4.5-rc1):
> 
> goldfish/goldfish_nand.c: In function 'goldfish_nand_erase':
> goldfish/goldfish_nand.c:107:91: error: comparison of distinct pointer types lacks a cast [-Werror]
> goldfish/goldfish_nand.c: In function 'goldfish_nand_read_oob':
> goldfish/goldfish_nand.c:145:91: error: comparison of distinct pointer types lacks a cast [-Werror]
> 
> This changes the code to the equivalent div_s64{,_rem} that
> works correctly for negative numbers (which we should never
> get here).

We can't get negatives as you say so surely the right fix is a cast or to
fix mtd->writesize ?

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#1323286

On Monday 01 February 2016 14:54:57 One Thousand Gnomes wrote:
> On Mon, 01 Feb 2016 11:33 +0100
> Arnd Bergmann <arnd@arndb.de> wrote:
> 
> > The goldfish nand driver divides a signed 64-bit number (loff_t)
> > in multiple places using the do_div() function. This has always
> > been unreliable but now produces a compiler warning (since 4.5-rc1):
> > 
> > goldfish/goldfish_nand.c: In function 'goldfish_nand_erase':
> > goldfish/goldfish_nand.c:107:91: error: comparison of distinct pointer types lacks a cast [-Werror]
> > goldfish/goldfish_nand.c: In function 'goldfish_nand_read_oob':
> > goldfish/goldfish_nand.c:145:91: error: comparison of distinct pointer types lacks a cast [-Werror]
> > 
> > This changes the code to the equivalent div_s64{,_rem} that
> > works correctly for negative numbers (which we should never
> > get here).
> 
> We can't get negatives as you say so surely the right fix is a cast or to
> fix mtd->writesize ?

A cast won't work because the first argument to the do_div() macro is
both input and output.

It's not the mtd->writesize argument that is the problem here, but the
'ofs' argument that comes from the loff_t argument in mtdchar_read()
and others (ultimately from the lseek/pread/pwrite/...)

We could change all the function prototypes in struct mtd_info to use
u64 instead of loff_t, but that involve change all MTD drivers and the
subsystem.

	Arnd

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#1324260

On Mon, 01 Feb 2016 11:33 +0100
Arnd Bergmann <arnd@arndb.de> wrote:

> The goldfish nand driver divides a signed 64-bit number (loff_t)
> in multiple places using the do_div() function. This has always
> been unreliable but now produces a compiler warning (since 4.5-rc1):
> 
> goldfish/goldfish_nand.c: In function 'goldfish_nand_erase':
> goldfish/goldfish_nand.c:107:91: error: comparison of distinct pointer types lacks a cast [-Werror]
> goldfish/goldfish_nand.c: In function 'goldfish_nand_read_oob':
> goldfish/goldfish_nand.c:145:91: error: comparison of distinct pointer types lacks a cast [-Werror]
> 
> This changes the code to the equivalent div_s64{,_rem} that
> works correctly for negative numbers (which we should never
> get here).
> 
> The warning has shown up on ARM allmodconfig builds after the goldfish
> bus driver has become visible on ARM.
> 
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> Fixes: bd2f348db503 ("goldfish: refactor goldfish platform configs")

Acked-by: Alan Cox <alan@linux.intel.com>

Now agree with Arnd's patch.

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