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

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Date:   Thu, 3 Aug 2023 19:01:34 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Adam Ford <aford173@...il.com>,
        Aleksandr Nogikh <nogikh@...gle.com>
Cc:     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

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

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.

-- 
~Randy