Re: linux-next: build failure after merge of the driver-core tree

Jeffrey Hugo
2023-04-11T18:37:49Z

On 4/11/2023 12:21 PM, Daniel Vetter wrote:
> On Tue, Apr 11, 2023 at 11:18:29AM -0600, Jeffrey Hugo wrote:
>> On 4/11/2023 10:31 AM, Daniel Vetter wrote:
>>> On Tue, Apr 11, 2023 at 09:29:27AM -0600, Jeffrey Hugo wrote:
>>>> On 4/11/2023 9:26 AM, Jeffrey Hugo wrote:
>>>>> On 4/11/2023 9:13 AM, Greg KH wrote:
>>>>>> On Tue, Apr 11, 2023 at 09:08:39AM -0600, Jeffrey Hugo wrote:
>>>>>>> On 4/11/2023 9:01 AM, Daniel Vetter wrote:
>>>>>>>> On Tue, Apr 11, 2023 at 12:40:28PM +0200, Greg KH wrote:
>>>>>>>>> On Tue, Apr 11, 2023 at 11:55:20AM +0200, Daniel Vetter wrote:
>>>>>>>>>> On Tue, Apr 11, 2023 at 02:38:12PM +1000, Stephen Rothwell wrote:
>>>>>>>>>>> Hi all,
>>>>>>>>>>>
>>>>>>>>>>> After merging the driver-core tree, today's linux-next build (x86_64
>>>>>>>>>>> allmodconfig) failed like this:
>>>>>>>>>>>
>>>>>>>>>>> In file included from include/linux/linkage.h:7,
>>>>>>>>>>>                    from include/linux/kernel.h:17,
>>>>>>>>>>>                    from drivers/accel/qaic/mhi_qaic_ctrl.c:4:
>>>>>>>>>>> drivers/accel/qaic/mhi_qaic_ctrl.c: In function
>>>>>>>>>>> 'mhi_qaic_ctrl_init':
>>>>>>>>>>> include/linux/export.h:27:22: error: passing
>>>>>>>>>>> argument 1 of 'class_create' from incompatible
>>>>>>>>>>> pointer type
>>>>>>>>>>> [-Werror=incompatible-pointer-types]
>>>>>>>>>>>      27 | #define THIS_MODULE (&__this_module)
>>>>>>>>>>>         |                     ~^~~~~~~~~~~~~~~
>>>>>>>>>>>         |                      |
>>>>>>>>>>>         |                      struct module *
>>>>>>>>>>> drivers/accel/qaic/mhi_qaic_ctrl.c:544:38: note:
>>>>>>>>>>> in expansion of macro 'THIS_MODULE'
>>>>>>>>>>>     544 |         mqc_dev_class =
>>>>>>>>>>> class_create(THIS_MODULE,
>>>>>>>>>>> MHI_QAIC_CTRL_DRIVER_NAME);
>>>>>>>>>>>         |                                      ^~~~~~~~~~~
>>>>>>>>>>> In file included from include/linux/device.h:31,
>>>>>>>>>>>                    from include/linux/mhi.h:9,
>>>>>>>>>>>                    from drivers/accel/qaic/mhi_qaic_ctrl.c:5:
>>>>>>>>>>> include/linux/device/class.h:229:54: note:
>>>>>>>>>>> expected 'const char *' but argument is of type
>>>>>>>>>>> 'struct module *'
>>>>>>>>>>>     229 | struct class * __must_check
>>>>>>>>>>> class_create(const char *name);
>>>>>>>>>>>         |                                          ~~~~~~~~~~~~^~~~
>>>>>>>>>>> drivers/accel/qaic/mhi_qaic_ctrl.c:544:25:
>>>>>>>>>>> error: too many arguments to function
>>>>>>>>>>> 'class_create'
>>>>>>>>>>>     544 |         mqc_dev_class =
>>>>>>>>>>> class_create(THIS_MODULE,
>>>>>>>>>>> MHI_QAIC_CTRL_DRIVER_NAME);
>>>>>>>>>>>         |                         ^~~~~~~~~~~~
>>>>>>>>>>> include/linux/device/class.h:229:29: note: declared here
>>>>>>>>>>>     229 | struct class * __must_check
>>>>>>>>>>> class_create(const char *name);
>>>>>>>>>>>         |                             ^~~~~~~~~~~~
>>>>>>>>>>>
>>>>>>>>>>> Caused by commit
>>>>>>>>>>>
>>>>>>>>>>>     1aaba11da9aa ("driver core: class: remove
>>>>>>>>>>> module * from class_create()")
>>>>>>>>>>>
>>>>>>>>>>> interacting with commit
>>>>>>>>>>>
>>>>>>>>>>>     566fc96198b4 ("accel/qaic: Add mhi_qaic_cntl")
>>>>>>>>>>>
>>>>>>>>>>> from the drm tree.
>>>>>>>>>>>
>>>>>>>>>>> I have applied the following merge fix patch for today.
>>>>>>>>>>>
>>>>>>>>>>> From: Stephen Rothwell <sfr@canb.auug.org.au>
>>>>>>>>>>> Date: Tue, 11 Apr 2023 14:16:57 +1000
>>>>>>>>>>> Subject: [PATCH] fixup for "driver core: class:
>>>>>>>>>>> remove module * from class_create()"
>>>>>>>>>>>
>>>>>>>>>>> interacting with "accel/qaic: Add mhi_qaic_cntl"
>>>>>>>>>>>
>>>>>>>>>>> Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
>>>>>>>>>>
>>>>>>>>>> Thanks for the fixup. Since Dave is out I've made a
>>>>>>>>>> note about this in my
>>>>>>>>>> handover mail so it won't get lost in the drm-next
>>>>>>>>>> merge window pull. I
>>>>>>>>>> don't think we need any other coordination than
>>>>>>>>>> mention it in each pull to
>>>>>>>>>> Linus, topic tree seems overkill for this. Plus there's no way I can
>>>>>>>>>> untangle the drm tree anyway :-).
>>>>>>>>>
>>>>>>>>> Want me to submit a patch for the drm tree that moves this to use
>>>>>>>>> class_register() instead, which will make the
>>>>>>>>> merge/build issue go away
>>>>>>>>> for you?  That's my long-term goal here anyway, so converting this new
>>>>>>>>> code to this api today would be something I have to do eventually :)
>>>>>>>>
>>>>>>>> We kinda closed drm-next for feature work mostly already (just pulling
>>>>>>>> stuff in from subtrees), so won't really help for this merge window.
>>>>>>>>
>>>>>>>> For everything else I think this is up to Oded, I had no
>>>>>>>> idea qaic needed
>>>>>>>> it's entire own dev class and I don't want to dig into this
>>>>>>>> for the risk I
>>>>>>>> might freak out :-)
>>>>>>>>
>>>>>>>> Adding Oded.
>>>>>>>>
>>>>>>>> Cheers, Daniel
>>>>>>>
>>>>>>> Sorry for the mess.
>>>>>>>
>>>>>>> I made a note to update to class_register() once my drm-misc access is
>>>>>>> sorted out.  Looks like we'll address the conflict in the merge
>>>>>>> window, and
>>>>>>> catch the update to the new API in the following release.
>>>>>>
>>>>>> Wait, I think the large question is, "why does this need a separate
>>>>>> class"?  Why are you not using the accel char device and class?  That is
>>>>>> what everything under accel/ should be using, otherwise why put it in
>>>>>> there?
>>>>>>
>>>>>> And what exactly are you using that class for?  Just device nodes?  If
>>>>>> so, how many?
>>>>>>
>>>>>> thanks,
>>>>>>
>>>>>> greg k-h
>>>>>
>>>>>
>>>>> Remember MHI_UCI that then evolved into the WWAN subsystem?  I pointed
>>>>> out at the time that AIC100/QAIC would need the same functionality.
>>>>> You/Jakub told myself/Mani/Loic that a combined implementation is not
>>>>> acceptable, and every area needs to implement their own version of
>>>>> MHI_UCI.
>>>>>
>>>>> We took the WWAN subsystem and simplified it to meet our needs.
>>>>>
>>>>> The functionality is QAIC specific, so wedging it into the Accel node
>>>>> seems to be a poor fit as it would subject Habana and iVPU to the same.
>>>>
>>>> Also, I forgot to mention. QAIC is sharing userspace components with WWAN,
>>>> so we really cannot diverge from what WWAN has done and define a new API
>>>> through the Accel node.
>>>
>>> So there is an accel/drm_device in the qaic driver, but there's also this
>>> different class thing, which I don't get.
>>>
>>> And yeah if that's an entirely orthogonal thing then I guess that should
>>> be in a different driver/subsystem, all supported with the aux bus to
>>> multiplex the underlying device.
>>>
>>> I haven't found any explanation for what MHI is (or any of the other
>>> acrynoms), so I'm entirely lost.
>>
>> MHI is documented at Documentation/mhi/
>> It is also referenced in the QAIC documentation - Documentation/accel/qaic/
>>
>> It stands for "Modem Host Interface" (arguably a bad name now, but you can
>> guess where it came from). It is a Qualcomm hardware block and associated
>> software protocol that provides logical channels over a hardware link. Most
>> commonly used for PCIe.
>>
>> Pretty much any modern Qualcomm PCIe device implements it. 4G modems, 5G
>> modems, Wifi adapters, AIC100, etc. Instead of talking "PCIe", the host
>> talks "MHI" to the devices in most cases.
>>
>> The core implementation for MHI exists in drivers/bus/mhi
>>
>> MHI_UCI is the MHI Userspace Character Interface. It looked like most buses
>> (eg USB) provide some direct device access to userspace. MHI_UCI was
>> formulated along those same lines - provide direct userspace access to a
>> whitelist of channels. Qualcomm provides some fairly extensive userspace
>> utilities, and various communities have developed open source alternatives
>> using this mechanism.
>>
>> MHI_UCI was proposed to the community as the common driver (misc device) for
>> all of the MHI devices. The Net folks came along, saw that it was used for
>> 4G/5G modems (Wireless Wide Area Network devices or WWAN) and decided that
>> they would not tolerate a common implementation. They NACK'd MHI_UCI and
>> required that a WWAN specific subsystem be developed which would only
>> service WWAN devices. The Net folks decreed that other subsystems which
>> needed the same functionality need to have their own copy of the
>> implementation.
>>
>> QAIC devices expose Sahara (a boot time protocol) which has an existing
>> userspace that is also used with Modems, although it looks like WWAN doesn't
>> currently support those generations of products today. QAIC devices also
>> support DIAG, which is currently supported in WWAN. The intent was to add
>> the QAIC support for DIAG at a later time since it is not required for the
>> bare minimum viable driver.
>>
>> So, QAIC devices support the same services, would use the same userspace,
>> but can't use a common implementation because Jakub(net) doesn't want to
>> share and convinced Greg to go along. I'm not interested in pushing a cross
>> tree fight (arguably already did that with MHI_UCI). If neither Greg nor
>> Net will accept a common implementation that accelerators can use (QAIC),
>> then the only place I can fit this is in the Accel area.
>>
>> Using aux bus seems to make little difference if QAIC is the only consumer
>> of this. I'm willing to refactor the implementation with some feedback and
>> guidence, but the uAPI seems set in stone due to the existing userspace and
>> WWAN (char devs with open/close/read/write/poll).
>
> Ok, so MHI _is_ the bus. Thanks for the explainer, I should have searched
> a bit more in Documentation/
>
>> What would make you less unhappy?
>
> The MHI generic userspace driver interface needs to be in drivers/bus/mhi,
> not in a random driver. I think we should revert 566fc96198b4
> ("accel/qaic: Add mhi_qaic_cntl") and re-land that through Greg's tree (or
> wherever mhi patches go to). This of course assuming that the accel
> userspace on top of the accel/drm_device does work stand-alone, and it's
> just the tooling and other userspace that needs MHI_UCI. If we end with a
> non-functional stack due to that, then I guess the entire driver is a bit
> up for questions, because at least the accel runtime is supposed to just
> run on top of the accel devnode and nothing else. Otherwise container
> stuff gets really bad, among a lot of other things.
>

Looping in the MHI maintainer for your proposal.

The accel userspace can work without MHI_UCI.

The revert will be non-trivial so I'll look at posting that tomorrow.

-Jeff