Skip to contentSkip to conversation

mtd: dc21285: fix bytewise memcpy()

PATCH In review Arnd Bergmann 3 participants 3 messages Aug 7, 2025 Memory technology devices (MTD)

lore
Share & tools
lore

Arnd Bergmann

author
#0 lore raw

PATCH 1/1 mtd: dc21285: fix bytewise memcpy()

From: Arnd Bergmann <[email protected]>

The commit that split up the 8/16/32-bit operations in 2004 seems to have broken the 8-bit case, as clang-21 now points out:

drivers/mtd/maps/dc21285.c:129:97: error: parameter 'len' set but not used [-Werror,-Wunused-but-set-parameter]
129 | static void dc21285_copy_to_8(struct map_info *map, unsigned long to, const void *from, ssize_t len)

Put back the loop that was in linux-2.6.8 and earlier for this case.

Fixes 67d4878e4e61 ("NOR flash drivers update")
Cc David Woodhouse <[email protected]>
Signed-off-by Arnd Bergmann <[email protected]>
---
 drivers/mtd/maps/dc21285.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)
drivers/mtd/maps/dc21285.c +8 -6
index 70a3db3ab856..1d70bf62e91f 100644
@@ -128,12 +128,14 @@ static void dc21285_copy_to_16(struct map_info *map, unsigned long to, const voi
 
 static void dc21285_copy_to_8(struct map_info *map, unsigned long to, const void *from, ssize_t len)
 {
-	map_word d;
-	d.x[0] = *((uint8_t*)from);
-	dc21285_write8(map, d, to);
-	from++;
-	to++;
-	len--;
+	while (len > 0) {
+		map_word d;
+		d.x[0] = *((uint8_t*)from);
+		dc21285_write8(map, d, to);
+		from++;
+		to++;
+		len--;
+	}
 }
 
 static struct map_info dc21285_map = {
Signature · 1 line
2.39.5
maintainer
#1 lore raw

Hello Arnd,

Quoted 5 lines · Arnd Bergmann

From: Arnd Bergmann <[email protected]>

The commit that split up the 8/16/32-bit operations in 2004 seems to have broken the 8-bit case, as clang-21 now points out:

Quoted 8 lines

drivers/mtd/maps/dc21285.c:129:97: error: parameter 'len' set but not used [-Werror,-Wunused-but-set-parameter]
129 | static void dc21285_copy_to_8(struct map_info *map, unsigned long to, const void *from, ssize_t len)

Put back the loop that was in linux-2.6.8 and earlier for this case.

Fixes 67d4878e4e61 ("NOR flash drivers update")
Cc David Woodhouse <[email protected]>
Signed-off-by Arnd Bergmann <[email protected]>

Thanks for the patch, I'll take it, but that probably means few to no people still use it, if broken for more than 20 years...

Cheers,
Miquèl

#2 lore raw
Quoted 11 lines · Miquel Raynal
Quoted 8 lines · Arnd Bergmann

From: Arnd Bergmann <[email protected]>

The commit that split up the 8/16/32-bit operations in 2004 seems to have broken the 8-bit case, as clang-21 now points out:

drivers/mtd/maps/dc21285.c:129:97: error: parameter 'len' set but not used [-Werror,-Wunused-but-set-parameter]
129 | static void dc21285_copy_to_8(struct map_info *map, unsigned long to, const void *from, ssize_t len)

Quoted 8 lines
Quoted 5 lines

Put back the loop that was in linux-2.6.8 and earlier for this case.

Fixes 67d4878e4e61 ("NOR flash drivers update")
Cc David Woodhouse <[email protected]>
Signed-off-by Arnd Bergmann <[email protected]>

Thanks for the patch, I'll take it, but that probably means few to no people still use it, if broken for more than 20 years...

Yes, certainly. I also have a patch to mark the mach-footbridge platform as deprecated and schedule it for removal, I need to resend that patch.

What I suspect happened here is that the bug was harmless because the few boards that use this driver all have 16-bit or 32-bit flashes, while the 8-bit codepath was indeed unused.

Arnd