Re: Adding deferred fbcon console takeover to the Fedora kernels

[Hans de Goede]

Hi,

On 30-07-18 20:46, Laura Abbott wrote:
> On 07/30/2018 08:18 AM, Hans de Goede wrote:
> > Hi,
> >
> > On 02-07-18 13:55, Hans de Goede wrote:
> > > Hi All,
> > >
> > > On 28-06-18 16:19, Hans de Goede wrote:
> > > > Hi All,
> > > >
> > > > Good news on the patch to make the loglevel for quiet configurable,
> > > > this has been accepted into -next now. I plan to add this to the
> > > > Fedora kernels soonish and set the quiet loglevel to 3 as
> > > > discussed earlier.
> > > >
> > > > Today another related patch-set got merged, see the last 3
> > > > commits here:
> > > > https://github.com/bzolnier/linux/commits/ib-fbdev-drm-v4.19-deferred-consol...
> > > >
> > > > I would also like to add these 3 patches to the Fedora 4.18
> > > > kernel (for F29+).
> > > >
> > > > The end goal here is a boot where the firmware shows its boot graphics
> > > > and these stay in place for a couple of seconds until the GUI loads and
> > > > the GUI then smoothly takes over the framebuffer without any disruptions.
> > > >
> > > > See here for an example of what this looks like on my main workstation:
> > > >
> > > > https://fedorapeople.org/~jwrdegoede/flickerfree-videos/workstation-normal.w...
> > > >
> > > > Shim has already been modified to leave the framebuffer as setup by
> > > > the firmware intact and patches for grub have been merged, but not
> > > > yet build for F29+.
> > > >
> > > > Combined with the hidden grub menu feature for F29:
> > > >
> > > > https://fedoraproject.org/wiki/Changes/HiddenGrubMenu
> > > >
> > > > This means that the framebuffer is still showing the boot graphics
> > > > (e.g. vendor logo) when the kernel loads.
> > > >
> > > > Without the "deferred fbcon console takeover" patches the fbcon
> > > > will takeover from dummycon as the console driver as soon as
> > > > the efifb registers itself as a fbdev, clearing the screen to
> > > > black. breaking the desired boot experience.
> > > >
> > > > The deferred console takeover patches make the fbcon code delay
> > > > taking over as the console until the first character is output
> > > > on the console.
> > > >
> > > > I've tested this code with the following scenarios:
> > > > Remove quiet from the kernel commandline -> fbcon binds right away
> > > >
> > > > because messages are logged to the dummycon before efifb loads
> > > > Mess up the root= kernel argument -> As soon as dracut prints
> > > >
> > > > its timeout message for finding the rootfs, fbcon binds and shows
> > > > the timeout message
> > > > Detailed view in plymouth mode (press ESC to show boot msg) ->
> > > >
> > > > plymouth retains drm master rights on /dev/dri/card? while it
> > > > tries to show the details. The blocks fbcon accessing the fbdev
> > > > device registered by the kms driver, so nothing will be shown
> > > > until plymouth exits (and releases the drm-master rights).
> > > >
> > > > This really is a plymouth bug, I've submitted plymouth patches
> > > > fixing this here:
> > > > https://bugs.freedesktop.org/show_bug.cgi?id=107047
> > >
> > > I got an ack from Ray for these patches and for adding these
> > > patches to the Fedora plymouth package as downstream patches
> > > (until the next upstream release). A new plymouth package
> > > fixing this is building now:
> > >
> > > https://koji.fedoraproject.org/koji/buildinfo?buildID=1102343
> >
> > I discussed adding these patches to the 4.18 / rawhide kernel
> > with Laura off-list and she said this was ok. So I've just
> > pushed the patches and the matching Kconfig changes.
> >
> > Regards,
> >
> > Hans
>
> s390 didn't seem to work:
> https://koji.fedoraproject.org/koji/taskinfo?taskID=28719549
>
> In function 'strncat',
>      inlined from 'iscsit_ta_authentication' at drivers/target/iscsi/iscsi_target_tpg.c:639:3:
> ./include/linux/string.h:313:10: warning: '__builtin_strncat' specified bound 1 equals source length [-Wstringop-overflow=]
>     return __builtin_strncat(p, q, count);
>            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> In function 'strncat',
>      inlined from 'iscsit_ta_authentication' at drivers/target/iscsi/iscsi_target_tpg.c:640:3:
> ./include/linux/string.h:313:10: warning: '__builtin_strncat' specified bound 4 equals source length [-Wstringop-overflow=]
>     return __builtin_strncat(p, q, count);
>            ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ERROR: "dummycon_unregister_output_notifier" [drivers/video/fbdev/core/fb.ko] undefined!
> ERROR: "dummycon_register_output_notifier" [drivers/video/fbdev/core/fb.ko] undefined!
> make[1]: *** [scripts/Makefile.modpost:92: __modpost] Error 1
>
> Looks like they might be missing EXPORT_SYMBOLS?

Yes there even is a patch for that in -next already, but this is only a
problem when building the fbdev code as a module so I did not catch
this while testing on x86_64.

I've added the necessary patch to the Fedora rawhide kernel now and
re-enabled this on s390x.

Regards,

Hans