Re: [PATCH v2] media: mali-c55: Fix scaler factor overflow for large crop sizes

[Dan Scally]

Hi David

On 18/06/2026 20:52, David Carlier wrote:
> The horizontal and vertical scaling factors multiply the crop dimensions
> by MALI_C55_RSZ_SCALER_FACTOR, a Q4.20 factor of (1 << 20). Both operands
> are 32-bit, so the multiplication wraps before the result is stored in
> the u64 scale variables. For any crop dimension of 4096 or more (the
> maximum is 8192) the value overflows; an 8192 to 4096 downscale yields a
> TINC of zero, so the scaler never advances and the output is corrupted.
>
> Define MALI_C55_RSZ_SCALER_FACTOR as a 64-bit constant so the
> multiplication is performed in 64-bit.
>
> Fixes: d5f281f3dd29 ("media: mali-c55: Add Mali-C55 ISP driver")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: David Carlier <devnexen@xxxxxxxxx>

Thanks very much:

Reviewed-by: Daniel Scally <dan.scally@xxxxxxxxxxxxxxxx>
> ---
>
> Notes:
>      v2: Define the macro as a 64-bit constant (BIT_ULL) instead of casting
>          each multiplication, per Dan's review.
>
>   drivers/media/platform/arm/mali-c55/mali-c55-resizer.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/media/platform/arm/mali-c55/mali-c55-resizer.c b/drivers/media/platform/arm/mali-c55/mali-c55-resizer.c
> index c4f46651d..6706939b4 100644
> --- a/drivers/media/platform/arm/mali-c55/mali-c55-resizer.c
> +++ b/drivers/media/platform/arm/mali-c55/mali-c55-resizer.c
> @@ -15,7 +15,7 @@
>   #include "mali-c55-registers.h"
>   
>   /* Scaling factor in Q4.20 format. */
> -#define MALI_C55_RSZ_SCALER_FACTOR	(1U << 20)
> +#define MALI_C55_RSZ_SCALER_FACTOR	BIT_ULL(20)
>   
>   #define MALI_C55_RSZ_COEFS_BANKS	8
>   #define MALI_C55_RSZ_COEFS_ENTRIES	64