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

[David CARLIER]

Hi Dan,

On Thu, 18 Jun 2026 at 20:35, Dan Scally <dan.scally@xxxxxxxxxxxxxxxx> wrote:
>
> Hi David, sorry this one slipped through the cracks
>
> On 10/06/2026 22:56, 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.
> >
> > Cast the crop dimensions to u64 before the multiplication.
> >
> > Fixes: d5f281f3dd29 ("media: mali-c55: Add Mali-C55 ISP driver")
> > Cc: stable@xxxxxxxxxxxxxxx
> > Signed-off-by: David Carlier <devnexen@xxxxxxxxx>
> > ---
> >   drivers/media/platform/arm/mali-c55/mali-c55-resizer.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > 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..0713e7d43 100644
> > --- a/drivers/media/platform/arm/mali-c55/mali-c55-resizer.c
> > +++ b/drivers/media/platform/arm/mali-c55/mali-c55-resizer.c
> > @@ -422,8 +422,8 @@ static int mali_c55_rsz_program_resizer(struct mali_c55_resizer *rsz,
> >       mali_c55_resizer_program_coefficients(rsz);
> >
> >       /* Program the V/H scaling factor in Q4.20 format. */
> > -     h_scale = crop->width * MALI_C55_RSZ_SCALER_FACTOR;
> > -     v_scale = crop->height * MALI_C55_RSZ_SCALER_FACTOR;
> > +     h_scale = (u64)crop->width * MALI_C55_RSZ_SCALER_FACTOR;
> > +     v_scale = (u64)crop->height * MALI_C55_RSZ_SCALER_FACTOR;
>
> Might be nicer to define the macro with ULL instead of a cast, what do you think?

even better, using BIT_ULL here ;) cheers.
>
> Thanks
> Dan
>
> >
> >       do_div(h_scale, scale->width);
> >       do_div(v_scale, scale->height);
>