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

From: David Laight <David.Laight@ACULAB.COM>
To: 'Maxime Ripard' <mripard@kernel.org>, Arnd Bergmann <arnd@arndb.de>
Cc: Naresh Kamboju <naresh.kamboju@linaro.org>,
	open list <linux-kernel@vger.kernel.org>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	"linux-sunxi@lists.linux.dev" <linux-sunxi@lists.linux.dev>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	"lkft-triage@lists.linaro.org" <lkft-triage@lists.linaro.org>,
	Dave Airlie <airlied@redhat.com>,
	"Dan Carpenter" <dan.carpenter@linaro.org>,
	Ard Biesheuvel <ardb@kernel.org>
Subject: RE: arm: ERROR: modpost: "__aeabi_uldivmod" [drivers/gpu/drm/sun4i/sun4i-drm-hdmi.ko] undefined!
Date: Sat, 9 Mar 2024 14:33:26 +0000	[thread overview]
Message-ID: <85b807289ff2400ea5887ced63655862@AcuMS.aculab.com> (raw)
In-Reply-To: <20240304-brawny-goshawk-of-sorcery-860cef@houat>

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);

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

	David

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