arm: ERROR: modpost: "__aeabi_uldivmod" [drivers/gpu/drm/sun4i/sun4i-drm-hdmi.ko] undefined!

[Geert Uytterhoeven]

On Sat, Mar 9, 2024 at 3:34 PM David Laight <David.Laight at aculab.com> wrote:
> From: Maxime Ripard
> > Sent: 04 March 2024 11:46
> >
> > On Mon, Mar 04, 2024 at 12:11:36PM +0100, Arnd Bergmann wrote:
> > > On Mon, Mar 4, 2024, at 09:07, Naresh Kamboju wrote:
> > > > The arm defconfig builds failed on today's Linux next tag next-20240304.
> > > >
> > > > Build log:
> > > > ---------
> > > > ERROR: modpost: "__aeabi_uldivmod"
> > > > [drivers/gpu/drm/sun4i/sun4i-drm-hdmi.ko] undefined!
> > > >
> > >
> > > Apparently caused by the 64-bit division in 358e76fd613a
> > > ("drm/sun4i: hdmi: Consolidate atomic_check and mode_valid"):
> > >
> > >
> > > +static enum drm_mode_status
> > > +sun4i_hdmi_connector_clock_valid(const struct drm_connector *connector,
> > > +                                const struct drm_display_mode *mode,
> > > +                                unsigned long long clock)
> > >  {
> > > -       struct sun4i_hdmi *hdmi = drm_encoder_to_sun4i_hdmi(encoder);
> > > -       unsigned long rate = mode->clock * 1000;
> > > -       unsigned long diff = rate / 200; /* +-0.5% allowed by HDMI spec */
> > > +       const struct sun4i_hdmi *hdmi = drm_connector_to_sun4i_hdmi(connector);
> > > +       unsigned long diff = clock / 200; /* +-0.5% allowed by HDMI spec */
> > >         long rounded_rate;
> > >
> > > This used to be a 32-bit division. If the rate is never more than
> > > 4.2GHz, clock could be turned back into 'unsigned long' to avoid
> > > the expensive div_u64().
> >
> > I sent a fix for it this morning:
> > https://lore.kernel.org/r/20240304091225.366325-1-mripard@kernel.org
> >
> > The framework will pass an unsigned long long because HDMI character
> > rates can go up to 5.9GHz.
>
> You could do:
>         /* The max clock is 5.9GHz, split the divide */
>         u32 diff = (u32)(clock / 8) / (200/8);

+1, as the issue is still present in current next, as per the recent
nagging from the build bots.

> The code should really use u32 and u64.
> Otherwise the sizes are different on 32bit.

The code is already using a variety of types (long, unsigned long long,
unsigned long) :-(

       max_t(unsigned long, rounded_rate, clock) -
       min_t(unsigned long, rounded_rate, clock) < diff)

At least u64 should make it very clear clock does not fit in 32-bit.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert at linux-m68k.org

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