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From:   Adam Ford <aford173@gmail.com>
Date:   Thu, 3 Aug 2023 10:24:44 -0500
Message-ID: <CAHCN7x+8Qq6w0eRC0NwBfhgS7XH7fmmPr9xwhR54rWFNY37Ugg@mail.gmail.com>
Subject: Re: drivers/gpu/drm/bridge/samsung-dsim.c link error
To:     Aleksandr Nogikh <nogikh@google.com>
Cc:     l.stach@pengutronix.de, inki.dae@samsung.com,
        jagan@amarulasolutions.com, m.szyprowski@samsung.com,
        airlied@gmail.com, daniel@ffwll.ch,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org,
        syzkaller@googlegroups.com, dvyukov@google.com
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On Thu, Aug 3, 2023 at 9:42=E2=80=AFAM Aleksandr Nogikh <nogikh@google.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_hsc=
lk
> >>> referenced by samsung-dsim.c:731 (drivers/gpu/drm/bridge/samsung-dsim=
.c:731)
> >>>               drivers/gpu/drm/bridge/samsung-dsim.o:(samsung_dsim_ini=
t) 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/m=
aster/dashboard/config/linux/upstream-arm64-kasan.config'
> $ make CC=3Dclang ARCH=3Darm64 LD=3Dld.lld CROSS_COMPILE=3Daarch64-linux-=
gnu- olddefconfig
>
> This also prints:
>
> WARNING: unmet direct dependencies detected for GENERIC_PHY_MIPI_DPHY
>   Depends on [n]: GENERIC_PHY [=3Dn]
>   Selected by [y]:
>   - DRM_NWL_MIPI_DSI [=3Dy] && DRM_BRIDGE [=3Dy] && DRM [=3Dy] && COMMON_=
CLK [=3Dy] && OF [=3Dy] && HAS_IOMEM [=3Dy]
>   - DRM_SAMSUNG_DSIM [=3Dy] && DRM [=3Dy] && DRM_BRIDGE [=3Dy] && COMMON_=
CLK [=3Dy] && OF [=3Dy] && HAS_IOMEM [=3Dy]
>
> $ make CC=3Dclang ARCH=3Darm64 LD=3Dld.lld CROSS_COMPILE=3Daarch64-linux-=
gnu- -j$(nproc)
>
> The kernel should have still compiled fine even despite the message above=
, right?
>
> 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=3Dy, so I don't think this is an issue.  I also checked the
multi_v7_defconfig for ARM and it also sets GENERIC_PHY=3Dy 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.

adam


>
> --
> Thank you!
> Aleksandr