We apologize for the inconvenience.  There is a large number of bugs to go through and several of them have gone stale. The kernel moves very fast so bugs may get fixed as part of a kernel update. Due to this, we are doing a mass bug update across all of the Fedora 26 kernel bugs.
 
Fedora 26 has now been rebased to 4.15.4-200.fc26.  Please test this kernel update (or newer) and let us know if you issue has been resolved or if it is still present with the newer kernel.
 
If you have moved on to Fedora 27, and are still experiencing this issue, please change the version to Fedora 27.
 
If you experience different issues, please open a new bug report for those.

This message is a reminder that Fedora 26 is nearing its end of life.
Approximately 4 (four) weeks from now Fedora will stop maintaining
and issuing updates for Fedora 26. It is Fedora's policy to close all
bug reports from releases that are no longer maintained. At that time
this bug will be closed as EOL if it remains open with a Fedora  'version'
of '26'.

Package Maintainer: If you wish for this bug to remain open because you
plan to fix it in a currently maintained version, simply change the 'version'
to a later Fedora version.

Thank you for reporting this issue and we are sorry that we were not
able to fix it before Fedora 26 is end of life. If you would still like
to see this bug fixed and are able to reproduce it against a later version
of Fedora, you are encouraged  change the 'version' to a later Fedora
version prior this bug is closed as described in the policy above.

Although we aim to fix as many bugs as possible during every release's
lifetime, sometimes those efforts are overtaken by events. Often a
more recent Fedora release includes newer upstream software that fixes
bugs or makes them obsolete.

Fedora 26 changed to end-of-life (EOL) status on 2018-05-29. Fedora 26
is no longer maintained, which means that it will not receive any
further security or bug fix updates. As a result we are closing this bug.

If you can reproduce this bug against a currently maintained version of
Fedora please feel free to reopen this bug against that version. If you
are unable to reopen this bug, please file a new report against the
current release. If you experience problems, please add a comment to this
bug.

Thank you for reporting this bug and we are sorry it could not be fixed.

This issue still exists.

/usr/src/kernels/5.3.6-200.fc30.x86_64]$ make mrproper
scripts/kconfig/conf  --syncconfig Kconfig
Kconfig:34: can't open file "Documentation/Kconfig"
make[3]: *** [scripts/kconfig/Makefile:73: syncconfig] Error 1
make[2]: *** [Makefile:562: syncconfig] Error 2
make[1]: *** [Makefile:678: include/config/auto.conf.cmd] Error 2
make: *** [Makefile:1409: _clean_.] Error 2

This is a problem because the entire Documentation directory is missing from kernel-devel

A work-around is to:

1) download the src rpm for the kernel you want from Koji ( https://koji.fedoraproject.org/koji/packageinfo?packageID=8 )
2) rpm2cpio <src rpm> | cpio --extract --make-directories
3) cd to the extracted rpm's directory
4) tar xf linux-*.tar.xz
5) cd linux-<version>
6) sudo cp -r Documentation /usr/src/kernel/<version>

(In reply to Corey Ashford from comment #6)
> A work-around is to:
> 
> 1) download the src rpm for the kernel you want from Koji (
> https://koji.fedoraproject.org/koji/packageinfo?packageID=8 )
> 2) rpm2cpio <src rpm> | cpio --extract --make-directories
> 3) cd to the extracted rpm's directory
> 4) tar xf linux-*.tar.xz
> 5) cd linux-<version>
> 6) sudo cp -r Documentation /usr/src/kernel/<version>

6) sudo cp -r Documentation /usr/src/kernels/<version>

*********** MASS BUG UPDATE **************

We apologize for the inconvenience.  There are a large number of bugs to go through and several of them have gone stale.  Due to this, we are doing a mass bug update across all of the Fedora 30 kernel bugs.

Fedora 30 has now been rebased to 5.5.7-100.fc30.  Please test this kernel update (or newer) and let us know if you issue has been resolved or if it is still present with the newer kernel.

If you have moved on to Fedora 31, and are still experiencing this issue, please change the version to Fedora 31.

If you experience different issues, please open a new bug report for those.

(In reply to Corey Ashford from comment #7)
> (In reply to Corey Ashford from comment #6)
> > A work-around is to:
> > 
> > 1) download the src rpm for the kernel you want from Koji (
> > https://koji.fedoraproject.org/koji/packageinfo?packageID=8 )
> > 2) rpm2cpio <src rpm> | cpio --extract --make-directories
> > 3) cd to the extracted rpm's directory
> > 4) tar xf linux-*.tar.xz
> > 5) cd linux-<version>
> > 6) sudo cp -r Documentation /usr/src/kernel/<version>
> 
> 6) sudo cp -r Documentation /usr/src/kernels/<version>

It's not just the documentation, I now see:

/usr/src/kernels/5.4.19-100.fc30.x86_64]₹ make mrproper
scripts/Makefile.clean:15: drivers/gpu/drm/arm/display/Makefile: No such file or directory
make[5]: *** No rule to make target 'drivers/gpu/drm/arm/display/Makefile'.  Stop.
make[4]: *** [scripts/Makefile.clean:67: drivers/gpu/drm/arm/display] Error 2
make[3]: *** [scripts/Makefile.clean:67: drivers/gpu/drm/arm] Error 2
make[2]: *** [scripts/Makefile.clean:67: drivers/gpu/drm] Error 2
make[1]: *** [scripts/Makefile.clean:67: drivers/gpu] Error 2
make: *** [Makefile:1657: _clean_drivers] Error 2

The source dir included with kernel-devel is not a full source tree. It is not intended for this to work.