Hi Laurent, On Tue, Jan 12, 2021 at 5:38 AM Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> wrote: > On Mon, Jan 11, 2021 at 01:57:02PM +0100, Geert Uytterhoeven wrote: > > As nwl_dsi.lanes is u32, and NSEC_PER_SEC is 1000000000L, the second > > multiplication in > > > > dsi->lanes * 8 * NSEC_PER_SEC > > > > will overflow on a 32-bit platform. Fix this by making the constant > > unsigned long long, forcing 64-bit arithmetic. > > > > While iMX8 is arm64, this driver is currently used on 64-bit platforms > > only, where long is 64-bit, so this cannot happen. But the issue may > > start to happen when the driver is reused for a 32-bit SoC, or when code > > is copied for a new driver. > > > > Signed-off-by: Geert Uytterhoeven <geert+renesas@xxxxxxxxx> > > --- a/drivers/gpu/drm/bridge/nwl-dsi.c > > +++ b/drivers/gpu/drm/bridge/nwl-dsi.c > > @@ -195,7 +195,7 @@ static u32 ps2bc(struct nwl_dsi *dsi, unsigned long long ps) > > u32 bpp = mipi_dsi_pixel_format_to_bpp(dsi->format); > > > > return DIV64_U64_ROUND_UP(ps * dsi->mode.clock * bpp, > > - dsi->lanes * 8 * NSEC_PER_SEC); > > + dsi->lanes * 8ULL * NSEC_PER_SEC); > > I wonder if we could get rid of a whole class of bugs by turning > NSEC_PER_SEC into a ULL, but I suppose there are valid cases where a > 32-bit integer is enough. Indeed, and 64-bit arithmetic is more expensive on 32-bit platforms. I considered that change, but doing so would require updates all over the place (e.g. printing a value derived from NSEC_PER_SEC, divisions that need to be changed to do_div or div_u64(), ...) Note that the selftests already use such a definition. > Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> Thanks! > How did you come across this by the way ? https://lore.kernel.org/linux-renesas-soc/CAMuHMdXQvPY_mYicjPKjDSCwdO_rP-9PJOvqD0J6=S3Opr1ycg@xxxxxxxxxxxxxx/ and of course I grepped for similar use patterns... Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
