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Date: Mon, 4 Mar 2024 11:24:41 +0000
From: Andre Przywara <andre.przywara@arm.com>
To: "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,
 dri-devel@lists.freedesktop.org, lkft-triage@lists.linaro.org, "Maxime
 Ripard" <mripard@kernel.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!
Message-ID: <20240304112441.707ded23@donnerap.manchester.arm.com>
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On Mon, 04 Mar 2024 12:11:36 +0100
"Arnd Bergmann" <arnd@arndb.de> wrote:

Hi,

> 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 */

Wouldn't "div_u64(clock, 200)" solve this problem?

Cheers,
Andre

>         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().
> 
>       Arnd
>