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

[Adam Ford]

On Thu, Aug 3, 2023 at 9:01 PM Randy Dunlap <rdunlap@xxxxxxxxxxxxx> wrote:
>
> Hi--
>
> On 8/3/23 08:24, Adam Ford wrote:
> > On Thu, Aug 3, 2023 at 9:42 AM Aleksandr Nogikh <nogikh@xxxxxxxxxx> 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?

Are you building linux-next or something else?  The .config file
generated when I build the arm64 defconfig  show both enabled:

$ grep GENERIC_PHY .config
CONFIG_GENERIC_PHY=y
CONFIG_GENERIC_PHY_MIPI_DPHY=y


> 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.

adam
>
> --
> ~Randy