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[71.184.137.158]) by smtp.gmail.com with ESMTPSA id r2-20020a05620a298200b0069fb54c2b4dsm103240qkp.31.2022.04.28.11.07.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 28 Apr 2022 11:07:40 -0700 (PDT) Message-ID: <03b38035c582d3c2616010a87a365e1eb62a81de.camel@redhat.com> Subject: Re: [PATCH v3] drm/display: Select DP helper for DRM_DP_AUX_CHARDEV and DRM_DP_CEC From: Lyude Paul To: Javier Martinez Canillas , linux-kernel@vger.kernel.org Cc: Jani Nikula , Thomas Zimmermann , Daniel Vetter , David Airlie , dri-devel@lists.freedesktop.org Date: Thu, 28 Apr 2022 14:07:39 -0400 In-Reply-To: <20220428082244.390859-1-javierm@redhat.com> References: <20220428082244.390859-1-javierm@redhat.com> Organization: Red Hat Inc. Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.42.4 (3.42.4-2.fc35) MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Reviewed-by: Lyude Paul On Thu, 2022-04-28 at 10:22 +0200, Javier Martinez Canillas wrote: > 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 > --- > > 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 >         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 >         select CEC_CORE >         help >           Choose this option if you want to enable HDMI CEC support for -- Cheers, Lyude Paul (she/her) Software Engineer at Red Hat