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SubjectRe: [PATCH v2] drm/display: Select DP helper for DRM_DP_AUX_CHARDEV and DRM_DP_CEC
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Hi

Am 27.04.22 um 23:55 schrieb Javier Martinez Canillas:
> The DRM_DP_AUX_CHARDEV and DRM_DP_CEC Kconfig symbols enable code that use
> DP helper functions, that are only present if CONFIG_DRM_DISPLAY_DP_HELPER
> is also enabled.
>
> But these don't select the DRM_DISPLAY_DP_HELPER symbol, meaning that it
> is possible to enable any of them without CONFIG_DRM_DISPLAY_DP_HELPER.
>
> That will lead to the following linking errors with the mentioned config:
>
> LD vmlinux.o
> MODPOST vmlinux.symvers
> MODINFO modules.builtin.modinfo
> GEN modules.builtin
> LD .tmp_vmlinux.kallsyms1
> KSYMS .tmp_vmlinux.kallsyms1.S
> AS .tmp_vmlinux.kallsyms1.S
> LD .tmp_vmlinux.kallsyms2
> KSYMS .tmp_vmlinux.kallsyms2.S
> AS .tmp_vmlinux.kallsyms2.S
> LD vmlinux
> SYSMAP System.map
> SORTTAB vmlinux
> OBJCOPY arch/arm64/boot/Image
> MODPOST modules-only.symvers
> ERROR: modpost: "drm_dp_dpcd_write" [drivers/gpu/drm/display/drm_display_helper.ko] undefined!
> ERROR: modpost: "drm_dp_read_desc" [drivers/gpu/drm/display/drm_display_helper.ko] undefined!
> ERROR: modpost: "drm_dp_dpcd_read" [drivers/gpu/drm/display/drm_display_helper.ko] undefined!
> make[1]: *** [scripts/Makefile.modpost:134: modules-only.symvers] Error 1
> make[1]: *** Deleting file 'modules-only.symvers'
> make: *** [Makefile:1749: modules] Error 2
>
> Note: It seems this has been an issue for a long time but was made easier
> to reproduce after the commit 1e0f66420b13 ("drm/display: Introduce a DRM
> display-helper module"). Adding a Fixes: tag just to make sure that this
> fix will be picked for stable once the mentioned change also lands there.
>
> Fixes: 1e0f66420b13 ("drm/display: Introduce a DRM display-helper module")
> Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
> ---
>
> Changes in v2:
> - Explain better the issue in the change description.
> - Only select DRM_DISPLAY_DP_HELPER and not DRM_DISPLAY_HELPER.
>
> drivers/gpu/drm/display/Kconfig | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/drivers/gpu/drm/display/Kconfig b/drivers/gpu/drm/display/Kconfig
> index f84f1b0cd23f..9fe80c4e555c 100644
> --- a/drivers/gpu/drm/display/Kconfig
> +++ b/drivers/gpu/drm/display/Kconfig
> @@ -32,6 +32,7 @@ config DRM_DISPLAY_HDMI_HELPER
> config DRM_DP_AUX_CHARDEV
> bool "DRM DP AUX Interface"
> depends on DRM
> + select DRM_DISPLAY_DP_HELPER

You cannot select DISPLAY_DP_HELPER without DISPLAY_HELPER.

Can't you simply make it depend on DISPLAY_DP_HELPER. The menu entry
will show up as soon as there's a driver that selcets DISPLAY_DP_HELPER.

Best regards
Thomas

> help
> Choose this option to enable a /dev/drm_dp_auxN node that allows to
> read and write values to arbitrary DPCD registers on the DP aux
> @@ -40,6 +41,7 @@ config DRM_DP_AUX_CHARDEV
> config DRM_DP_CEC
> bool "Enable DisplayPort CEC-Tunneling-over-AUX HDMI support"
> depends on DRM
> + select DRM_DISPLAY_DP_HELPER
> select CEC_CORE
> help
> Choose this option if you want to enable HDMI CEC support for

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
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