On Wed, 27 Oct 2021, Javier Martinez Canillas javierm@redhat.com wrote:
On 10/27/21 14:18, Arnd Bergmann wrote:
On Wed, Oct 27, 2021 at 1:47 PM Jani Nikula jani.nikula@linux.intel.com wrote:
[snip]
drm_fb_helper.o is not part of drm.ko, it's part of drm_kms_helper.ko. This adds some sort of indirect dependency via DRM which might work, maybe by coincidence, maybe not - but it's certainly not obvious.
Indeed, you are correct that's not semantically correct.
Right, how about this change on top?
--- a/drivers/gpu/drm/Kconfig +++ b/drivers/gpu/drm/Kconfig @@ -117,9 +117,8 @@ config DRM_DEBUG_MODESET_LOCK
config DRM_FBDEV_EMULATION bool "Enable legacy fbdev support for your modesetting driver"
depends on DRMdepends on FB=y || FB=DRMselect DRM_KMS_HELPER
depends on DRM_KMS_HELPERdepends on FB=y || FB=DRM_KMS_HELPER select FB_CFB_FILLRECT select FB_CFB_COPYAREA select FB_CFB_IMAGEBLITThat would probably make it work for DRM=y, FB=m, DRM_KMS_HELPER=m, but it needs more randconfig testing, which I can help with.
The likely culprit is, again, the overuse of select, and in this case select DRM_KMS_HELPER. And DRM_KMS_HELPER should depend on FB if DRM_FBDEV_EMULATION=y. That's the problem.
This is something we can't easily express in Kconfig, as we can't add the dependency to a symbol that only gets selected by other drivers, which is why the dependency has to be in the user-visible symbol, in this case DRM_FBDEV_EMULATION.
Why the dependency has to be in a user-visible symbol? What could be the problem with having something like:
diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig index cea777ae7fb9..f80b404946ca 100644 --- a/drivers/gpu/drm/Kconfig +++ b/drivers/gpu/drm/Kconfig @@ -82,6 +82,7 @@ config DRM_DEBUG_SELFTEST config DRM_KMS_HELPER tristate depends on DRM
depends on (DRM_FBDEV_EMULATION && FB) || !DRM_FBDEV_EMULATION
To me, this seems like the right solution. Depend on FB if DRM_FBDEV_EMULATION is enabled. That's exactly what the relationship is.
BR, Jani.
help CRTC helpers for KMS drivers.@@ -104,7 +105,6 @@ config DRM_FBDEV_EMULATION bool "Enable legacy fbdev support for your modesetting driver" depends on DRM depends on FB
select DRM_KMS_HELPER select FB_CFB_FILLRECT select FB_CFB_COPYAREA select FB_CFB_IMAGEBLITBest regards,