linux-kernel - Re: [PATCH] drm/rockchip: avoid 64-bit division

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Message-ID: <CAMuHMdUGfCWyFHnAKeg4YViErzX5BReb2A-8gtqECstUMn2Oeg@mail.gmail.com>
Date: Fri, 22 Nov 2024 10:33:03 +0100
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: Maxime Ripard <mripard@...nel.org>
Cc: Nathan Chancellor <nathan@...nel.org>, Arnd Bergmann <arnd@...nel.org>, Sandy Huang <hjc@...k-chips.com>, 
	Heiko Stübner <heiko@...ech.de>, 
	Andy Yan <andy.yan@...k-chips.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Thomas Zimmermann <tzimmermann@...e.de>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, 
	Algea Cao <algea.cao@...k-chips.com>, 
	Cristian Ciocaltea <cristian.ciocaltea@...labora.com>, Arnd Bergmann <arnd@...db.de>, 
	dri-devel@...ts.freedesktop.org, linux-arm-kernel@...ts.infradead.org, 
	linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/rockchip: avoid 64-bit division

Hi Maxime,

On Fri, Nov 22, 2024 at 10:15 AM Maxime Ripard <mripard@...nel.org> wrote:
> On Fri, Nov 22, 2024 at 09:36:16AM +0100, Geert Uytterhoeven wrote:
> > On Mon, Nov 4, 2024 at 6:30 PM Nathan Chancellor <nathan@...nel.org> wrote:
> > > On Fri, Oct 18, 2024 at 03:10:10PM +0000, Arnd Bergmann wrote:
> > > > From: Arnd Bergmann <arnd@...db.de>
> > > >
> > > > Dividing a 64-bit integer prevents building this for 32-bit targets:
> > > >
> > > > ERROR: modpost: "__aeabi_uldivmod" [drivers/gpu/drm/rockchip/rockchipdrm.ko] undefined!
> > > >
> > > > As this function is not performance criticial, just Use the div_u64() helper.
> > > >
> > > > Fixes: 128a9bf8ace2 ("drm/rockchip: Add basic RK3588 HDMI output support")
> > > > Signed-off-by: Arnd Bergmann <arnd@...db.de>
> > >
> > > Reviewed-by: Nathan Chancellor <nathan@...nel.org>
> > >
> > > Can someone please pick this up? It is still broken in next-20241104...
> > >
> > > https://storage.tuxsuite.com/public/clangbuiltlinux/continuous-integration2/builds/2oNvJFRj8tkDieb6VfrMf4rh1Kn/build.log
> > >
> > > > ---
> > > >  drivers/gpu/drm/rockchip/dw_hdmi_qp-rockchip.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/rockchip/dw_hdmi_qp-rockchip.c b/drivers/gpu/drm/rockchip/dw_hdmi_qp-rockchip.c
> > > > index 9c796ee4c303..c8b362cc2b95 100644
> > > > --- a/drivers/gpu/drm/rockchip/dw_hdmi_qp-rockchip.c
> > > > +++ b/drivers/gpu/drm/rockchip/dw_hdmi_qp-rockchip.c
> > > > @@ -82,7 +82,7 @@ static void dw_hdmi_qp_rockchip_encoder_enable(struct drm_encoder *encoder)
> > > >                * comment in rk_hdptx_phy_power_on() from
> > > >                * drivers/phy/rockchip/phy-rockchip-samsung-hdptx.c
> > > >                */
> > > > -             phy_set_bus_width(hdmi->phy, rate / 100);
> > > > +             phy_set_bus_width(hdmi->phy, div_u64(rate, 100));
> > > >       }
> > > >  }
> >
> > noreply@...erman.id.au has just told me this build issue is now upstream:
> >
> >     FAILED linus/m68k-allmodconfig/m68k-gcc8.1 Fri Nov 22, 05:34
> >     http://kisskb.ellerman.id.au/kisskb/buildresult/15277242/
> >
> >     Commit:   Merge tag 'drm-next-2024-11-21' of
> > https://gitlab.freedesktop.org/drm/kernel
> >               28eb75e178d389d325f1666e422bc13bbbb9804c
> >     Compiler: m68k-linux-gcc (GCC) 8.1.0 / GNU ld (GNU Binutils) 2.30
> >
> >     ERROR: modpost: "__udivdi3"
> > [drivers/gpu/drm/rockchip/rockchipdrm.ko] undefined!
> >
> > Applying this patch fixes it, so
> > Acked-by: Geert Uytterhoeven <geert@...ux-m68k.org>
> >
> > Do we really need +5 weeks to apply a fix for a reported build issue?
>
> Do we really need that kind of comments?

Perhaps not...

> It was applied already,

Where was it applied?
How would I know that, when the fix is not in linux-next?

> I made sure it's part of the next PR we send to
> Linus. And it should be in linux-next tomorrow.

Thank you!

The issue is that the reported build issue was not fixed in linux-next,
despite the fix having been available for 5 weeks, thus reducing
(build) test coverage for all affected architectures, possibly hiding
other issues.
In addition, a PR including the build issue was sent to Linus, so now
the above applies to Linus' tree, too.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-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