Re: [PATCH v3] drm/display: Select DP helper for DRM_DP_AUX_CHARDEV and DRM_DP_CEC

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Hi

Am 28.04.22 um 10:22 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

Besides making these symbols to select CONFIG_DRM_DISPLAY_DP_HELPER, make
them to depend on DRM_DISPLAY_HELPER, since can't be enabled without it.

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@xxxxxxxxxx>
---

Changes in v3:
- Also make DRM_DP_AUX_CHARDEV and DRM_DP_CEC depend on DRM_DISPLAY_HELPER
   (Thomas Zimmermann).

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 | 6 ++++--
  1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/display/Kconfig b/drivers/gpu/drm/display/Kconfig
index f84f1b0cd23f..1b6e6af37546 100644
--- a/drivers/gpu/drm/display/Kconfig
+++ b/drivers/gpu/drm/display/Kconfig
@@ -31,7 +31,8 @@ config DRM_DISPLAY_HDMI_HELPER
config DRM_DP_AUX_CHARDEV
  	bool "DRM DP AUX Interface"
-	depends on DRM
+	depends on DRM && DRM_DISPLAY_HELPER
+	select DRM_DISPLAY_DP_HELPER

I'd be OK with that, but I'm still wondering why you're not making it depend on DRM_DISPLAY_DP_HELPER. If a config only enables HDMI (without DP), these options would still show up.


  	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
@@ -39,7 +40,8 @@ config DRM_DP_AUX_CHARDEV
config DRM_DP_CEC
  	bool "Enable DisplayPort CEC-Tunneling-over-AUX HDMI support"
-	depends on DRM
+	depends on DRM && DRM_DISPLAY_HELPER
+	select DRM_DISPLAY_DP_HELPER

Same here.

Best regards
Thomas

  	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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