Hi Marc, On 16/11/2020 21:07, Marc Zyngier wrote: > Hi all, > > Having recently moved over to a top-of-the-tree u-boot on one of my > VIM3L systems in order to benefit from unrelated improvements > (automatic PCIe detection, EFI...), I faced the issue that my kernel > would hang like this: > > [ OK ] Finished Helper to synchronize boot up for ifupdown. > [ OK ] Started Rule-based Manager for Device Events and Files. > [ 7.114516] VDDCPU: supplied by regulator-dummy > [ OK ] Found device /dev/ttyAML0. > [ 7.146862] meson-drm ff900000.vpu: Queued 2 outputs on vpu > [ 7.169630] fb0: switching to meson-drm-fb from simple > [ 7.169944] Console: switching to colour dummy device 80x25 > [ 7.179250] meson-drm ff900000.vpu: CVBS Output connector not available > > and that's it. > > After some poking around, I figured out that it is in the > meson-dw-hdmi module that the CPU was hanging... I'll be interested in having your kernel config, I never had such report since I enabled HDMI support in U-Boot a few years ago. > > Reverting to the kernel DT instead of u-boot's papered over it > somehow, but it turned out that removing the module (modprobe -r) > resulted in a firework. And for every issue I was fixing, another > followed. Much fun for a rainy Monday in the basement! > > I ended up with the following 4 patches, which solve all my problems: > I can now boot with the u-boot provided DT, and the hdmi and DRM > drivers can be removed and re-inserted at will. > > The first patch is a straightforward use-after-free, causing a NULL > pointer dereference. Moving things around fixes it. > > The second patch shows that I have no clue about the DRM subsystem > whatsoever. I mimicked what my Rockchip systems are doing, and the two > warnings disappeared. It can't completely be wrong (famous last > words...). > > The third patch fixes a *very* common issue with regulators (I've > fixed at least 3 drivers with a similar issue). I guess the devm > subsystem needs to grow a new helper at some point. > > The last patch finally fixes the issue I was seeing: the HDMI driver > hangs when accessing a register with clocks disabled, which they are > on module removal. It also fixes my u-boot booting for similar > reasons, I guess. Anyway, thanks for fixing this ! > > I went as far as reaching out for a HDMI cable and verifying that I > was getting a working display. Total dedication. This is very appreciated :-) > > Feedback much appreciated. > > M. > > Marc Zyngier (4): > drm/meson: Free RDMA resources after tearing down DRM > drm/meson: Unbind all connectors on module removal > drm/meson: dw-hdmi: Register a callback to disable the regulator > drm/meson: dw-hdmi: Ensure that clocks are enabled before touching the > TOP registers > > drivers/gpu/drm/meson/meson_drv.c | 12 +++++++----- > drivers/gpu/drm/meson/meson_dw_hdmi.c | 13 +++++++++++-- > 2 files changed, 18 insertions(+), 7 deletions(-) > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
