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

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Message-ID: <b43e642d-8aa1-fb8a-6bff-86039a06d57b@infradead.org>
Date:   Thu, 3 Aug 2023 19:47:11 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Adam Ford <aford173@...il.com>
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 8/3/23 19:42, Adam Ford wrote:
> 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.
> 

Nor am I. Alexsandr can hopefully tell us.

>>
>>> 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
>>

Not necessarily. It could be generated by 'make randconfig'.

>>>
>>>> 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

-- 
~Randy