From: Arnd Bergmann <arnd@arndb.de>

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 <dwmw2@infradead.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/mtd/maps/dc21285.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/mtd/maps/dc21285.c b/drivers/mtd/maps/dc21285.c
index 70a3db3ab856..1d70bf62e91f 100644
--- a/drivers/mtd/maps/dc21285.c
+++ b/drivers/mtd/maps/dc21285.c
@@ -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 = {
-- 
2.39.5

Hello Arnd,

On 07/08/2025 at 09:20:34 +02, Arnd Bergmann <arnd@kernel.org> wrote:

> From: Arnd Bergmann <arnd@arndb.de>
>
> 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 <dwmw2@infradead.org>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

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

On Thu, Aug 7, 2025, at 09:54, Miquel Raynal wrote:
>
> On 07/08/2025 at 09:20:34 +02, Arnd Bergmann <arnd@kernel.org> wrote:
>
>> From: Arnd Bergmann <arnd@arndb.de>
>>
>> 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 <dwmw2@infradead.org>
>> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
>
> 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