On Wed, Mar 16, 2022 at 8:31 PM Thomas Zimmermann <tzimmermann@xxxxxxx> wrote: > Am 16.03.22 um 20:12 schrieb Thomas Zimmermann: > >> > >> Adding a dependency in all drivers that select DRM_MIPI_DBI avoids > >> the problem for now, adding the dependency in DRM_MIPI_DBI as well > >> should help make it easier to figure out why it breaks if someone > >> forgets the dependency the next time. > >> > >> tristate > >> - depends on DRM > >> + depends on DRM_KMS_HELPER > > > > This symbol cannot be selected by users, so it's maybe not a good idea > > to depend on it. In fact, I've had to remove such a statement because it > > created a cyclic dependency. [1] I tried to explain above what I was thinking here: the added dependency is both a correct statement (DRM_MIPI_DBI depends on DRM_KMS_HELPER because it cannot be built without DRM_KMS_HELPER) and helpful as an indication what went wrong if we run into the same problem with a new driver, instead of the cryptic link failure you get something like WARNING: unmet direct dependencies detected for DRM_MIPI_DBI Depends on [m]: HAS_IOMEM [=y] && DRM_KMS_HELPER [=m] Selected by [y]: - DRM_PANEL_WIDECHIPS_WS2401 [=y] && HAS_IOMEM [=y] && DRM [=y] && DRM_PANEL [=y] && SPI [=y] && GPIOLIB [=y] && BACKLIGHT_CLASS_DEVICE [=y] Selected by [m]: - TINYDRM_ILI9225 [=m] && HAS_IOMEM [=y] && DRM [=y] && SPI [=y] > [1] > https://lore.kernel.org/dri-devel/20220315084559.23510-1-tzimmermann@xxxxxxx/ I was going for 'depends on' in the panel drivers because I saw the same being done for other panel drivers, and mixing the two methods causes dependency loops. I looked again now, and find that 'select DRM_KMS_HELPER' is more common for other drivers, and makes sense here because it is generally not user-selectable. The easiest replacement for my patch would then be to just use 'select DRM_KMS_HELPER' from CONFIG_DRM_MIPI_DBI, which makes it safer and more consistent with your change. If you like, I'll send an updated version. One thing I'm not sure about is whether there is still use for ever having CONFIG_DRM without CONFIG_DRM_KMS_HELPER if it gets selected by almost every driver anyway. Is this actually a configuration that users rely on, or should we just remove the symbol completely and build the KMS helpers unconditionally? Arnd
