linux-kernel - Re: drivers/gpu/drm/bridge/samsung-dsim.c link error

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Message-ID: <CAHCN7xKnRAmKh60dAtVaxz-dQtjzhBNtS0aN2swmddfo5FAD-Q@mail.gmail.com>
Date:   Thu, 3 Aug 2023 21:42:41 -0500
From:   Adam Ford <aford173@...il.com>
To:     Randy Dunlap <rdunlap@...radead.org>
Cc:     Aleksandr Nogikh <nogikh@...gle.com>, l.stach@...gutronix.de,
        inki.dae@...sung.com, jagan@...rulasolutions.com,
        m.szyprowski@...sung.com, airlied@...il.com, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        syzkaller@...glegroups.com, dvyukov@...gle.com
Subject: Re: drivers/gpu/drm/bridge/samsung-dsim.c link error

On Thu, Aug 3, 2023 at 9:37 PM Randy Dunlap <rdunlap@...radead.org> wrote:
>
>
>
> On 8/3/23 19:26, Adam Ford wrote:
> > On Thu, Aug 3, 2023 at 9:01 PM Randy Dunlap <rdunlap@...radead.org> wrote:
> >>
> >> Hi--
> >>
> >> On 8/3/23 08:24, Adam Ford wrote:
> >>> On Thu, Aug 3, 2023 at 9:42 AM Aleksandr Nogikh <nogikh@...gle.com> wrote:
> >>>>
> >>>> Hello,
> >>>>
> >>>> We've been seing the following linker error on arm64 syzbot instances:
> >>>>
> >>>> ld.lld: error: undefined symbol: phy_mipi_dphy_get_default_config_for_hsclk
> >>>>>>> referenced by samsung-dsim.c:731 (drivers/gpu/drm/bridge/samsung-dsim.c:731)
> >>>>>>>               drivers/gpu/drm/bridge/samsung-dsim.o:(samsung_dsim_init) in archive vmlinux.a
> >>>>
> >>>> Steps to reproduce on the latest linux-next:
> >>>>
> >>>> $ git checkout next-20230803
> >>>> $ wget -O '.config' 'https://raw.githubusercontent.com/google/syzkaller/master/dashboard/config/linux/upstream-arm64-kasan.config'
> >>>> $ make CC=clang ARCH=arm64 LD=ld.lld CROSS_COMPILE=aarch64-linux-gnu- olddefconfig
> >>>>
> >>>> This also prints:
> >>>>
> >>>> WARNING: unmet direct dependencies detected for GENERIC_PHY_MIPI_DPHY
> >>>>   Depends on [n]: GENERIC_PHY [=n]
> >>>>   Selected by [y]:
> >>>>   - DRM_NWL_MIPI_DSI [=y] && DRM_BRIDGE [=y] && DRM [=y] && COMMON_CLK [=y] && OF [=y] && HAS_IOMEM [=y]
> >>>>   - DRM_SAMSUNG_DSIM [=y] && DRM [=y] && DRM_BRIDGE [=y] && COMMON_CLK [=y] && OF [=y] && HAS_IOMEM [=y]
> >>>>
> >>>> $ make CC=clang ARCH=arm64 LD=ld.lld CROSS_COMPILE=aarch64-linux-gnu- -j$(nproc)
> >>>>
> >>>> The kernel should have still compiled fine even despite the message above, right?
> >>
> >> No. See drivers/Makefile:
> >> obj-$(CONFIG_GENERIC_PHY)       += phy/
> >>
> >> so the drivers/phy/ subdir is only built when CONFIG_GENERIC_PHY is set,
> >> but it's not set.
> >>
> >>>> Could you please take a look?
> >>>
> >>> GENERIC_PHY_MIPI_DPHY was enabled to use
> >>> phy_mipi_dphy_get_default_config() which takes in the pixel clock,
> >>> bits-per-pixel, number of lanes and phy structure.  It applies a bunch
> >>> of math based on the info passed and fills in the structure, but that
> >>> function itself doesn't appear to be referencing phy code, so it's
> >>> likely safe.
> >>>
> >>> I think this can be resolved by enabling GENERIC_PHY.  I just checked
> >>> linux-next and when I built the arm64 defconfig, it enables
> >>> GENERIC_PHY=y, so I don't think this is an issue.  I also checked the
> >>
> >> defconfig doesn't matter in this case. The .config that was provided has:
> >> # CONFIG_GENERIC_PHY is not set
> >> CONFIG_GENERIC_PHY_MIPI_DPHY=y
> >>
> >
> > Where/how was the .config generated?
> >
>
> Aleksandr posted a link to the config file above.

I get that, but I am not sure how this was generated.

>
> > Are you building linux-next or something else?  The .config file
> > generated when I build the arm64 defconfig  show both enabled:
>
> linux-next.
>
>
> > $ grep GENERIC_PHY .config
> > CONFIG_GENERIC_PHY=y
> > CONFIG_GENERIC_PHY_MIPI_DPHY=y
> >
>
> Yes, this is not a defconfig file.

I know, but it is a .config file that is generated from make defconfig
ARCH=arm64
>
> >
> >> but yes, selecting GENERIC_PHY (needed in 3 places) does fix the warnings
> >> and build error.  2 instance in drm/bridge/Kconfig and one in
> >> drm/bridge/cadence/Kconfig (found by inspection).
> >>
> >>
> >>
> >>> multi_v7_defconfig for ARM and it also sets GENERIC_PHY=y for 32-bit
> >>> ARM people using some of the Exynos boards.
> >>>
> >>> I don't know what version of Linux you're trying to build, but I can't
> >>> replicate your issue.
> >>
> >> I had no problem replicating the kconfig warnings and build error.
> >
> > If you can replicate the problem, I'd suggest submitting a patch.
>
> Sure, I'll do that.

Great!  thanks.

adam
>
> --
> ~Randy