ACK: Re: [SRU][N][PATCH 0/1] fbdev: Introduce devm_register_framebuffer()

[Paolo Pisati]

On Sun, Oct 19, 2025 at 11:19:07AM +0000, marcin.wilk at canonical.com wrote:
> From: Marcin Wilk <marcin.wilk at canonical.com>
> 
> BugLink: https://bugs.launchpad.net/bugs/2127971
> 
> SRU Justification:
> 
> [ Impact ]
> 
> Ubuntu x86_64 6.8 kernels won't build if CONFIG_FB_HYPERV config option is enabled (m/y). The build process fails with the following error:
> drivers/video/fbdev/hyperv_fb.c: In function ‘hvfb_probe’:
> drivers/video/fbdev/hyperv_fb.c:1195:15: error: implicit declaration of function ‘devm_register_framebuffer’; did you mean ‘unregister_framebuffer’? [-Werror=implicit-function-declaration]
>  1195 | ret = devm_register_framebuffer(&hdev->device, info);
>       | ^~~~~~~~~~~~~~~~~~~~~~~~~
>       | unregister_framebuffer
>   CC lib/objpool.o
>   CC [M] sound/pci/emu10k1/io.o
> cc1: some warnings being treated as errors
> make[5]: *** [scripts/Makefile.build:243: drivers/video/fbdev/hyperv_fb.o] Error 1
> make[4]: *** [scripts/Makefile.build:481: drivers/video/fbdev] Error 2
> make[3]: *** [scripts/Makefile.build:481: drivers/video] Error 2
> make[2]: *** [scripts/Makefile.build:481: drivers] Error 2
> 
> The reason is that in the 6.8 Ubuntu kernel source, commit f26c2008d5bd6d (cherry pick from upstream ea2f45ab0e53b255) introduced call to 'devm_register_framebuffer', but there is missing an upstream commit 929c81ade6355b, which provides the implementation for 'devm_register_framebuffer'. This SRU adds the missing upstream commit 929c81ade6355b to the 6.8 Ubuntu kernel source.
> 
> This issue hasn't been noticed because, by default, the CONFIG_FB_HYPERV is disabled for Ubuntu kernel builds:
> ./debian/scripts/misc/annotations --query --config CONFIG_FB_HYPERV
> {
>   "CONFIG_FB_HYPERV": {
>     "policy": {
>       "amd64": "n",
>       "arm64": "n"
>     }
>   }
> }
> 
> [ Test Plan ]
> 
> With the patch applied to the Noble kernel source:
> 1. enable the CONFIG_FB_HYPERV
> echo 'CONFIG_FB_HYPERV=m' > ~/test-config
> ./debian/scripts/misc/annotations --arch amd64 --flavour generic --update ~/test-config
> 2. clean and confirm the change
> fakeroot debian/rules clean updateconfigs
> ./debian/scripts/misc/annotations --query --config CONFIG_FB_HYPERV
> 3. build the kernel
> fakeroot debian/rules clean binary-generic
> 
> The kernel will build without any errors. Without the patch, it would fail with the aforementioned error.
> 
> [ Where problems could occur]
> 
> Regression risk is low because:
> 1. Impact is limited to the builds (and kernels built) with CONFIG_FB_HYPERV enabled. This option is disabled by default for Ubuntu.
> 2. The patch has already landed in more recent Ubuntu kernels, ie 6.14 HWE, and it's been there for a while:
> git branch -a --contains 929c81ade6355b
>   contains
>   remotes/origin/hwe-6.14-next
>   remotes/origin/hwe-6.14-next--2025.06.16-1--auto
>   remotes/origin/hwe-6.14-next--2025.06.16-3--auto
>   remotes/origin/hwe-6.14-next--2025.06.16-6--auto
>   remotes/origin/hwe-6.14-next--2025.07.14-1--auto
>   remotes/origin/hwe-6.14-next--2025.07.14-3--auto
>   remotes/origin/hwe-6.14-next--2025.08.11-1--auto
>   remotes/origin/hwe-6.14-next--2025.09.15-1--auto
>   remotes/origin/hwe-6.14-next--2025.10.13-1--auto
>   remotes/origin/hwe-6.14-next--s2025.05.19-1--auto
>   remotes/origin/hwe-6.14-next--s2025.06.16-1--auto
>   remotes/origin/hwe-6.14-next--s2025.06.16-3--auto
>   remotes/origin/hwe-6.14-next--s2025.07.14-1--auto
>   remotes/origin/hwe-6.14-next--s2025.08.11-1--auto
>   remotes/origin/hwe-6.14-next--s2025.09.15-1--auto
> 
> [ Other Info ]
> 
> The problem was identified by a Customer who rebuils the Bluefield [1] kernel for x86_64 with the CONFIG_FB_HYPERV enabled.
> 
> [1] https://git.launchpad.net/~canonical-kernel-bluefield/ubuntu/+source/linux-bluefield/+git/noble
> 
> Thomas Weißschuh (1):
>   fbdev: Introduce devm_register_framebuffer()
> 
>  drivers/video/fbdev/core/fbmem.c | 30 ++++++++++++++++++++++++++++++
>  include/linux/fb.h               |  1 +
>  2 files changed, 31 insertions(+)
> 
> -- 
> 2.43.0
> 
> 
> -- 
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> kernel-team at lists.ubuntu.com
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Acked-by: Paolo Pisati <paolo.pisati at canonical.com>
-- 
bye,
p.