From: Neil Armstrong <narmstrong@baylibre.com>
To: Marc Zyngier <maz@kernel.org>, Kevin Hilman <khilman@baylibre.com>
Cc: Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
linux-amlogic@lists.infradead.org, kernel-team@android.com,
linux-arm-kernel@lists.infradead.org,
Jerome Brunet <jbrunet@baylibre.com>
Subject: Re: [PATCH 0/4] drm/meson: Module removal fixes
Date: Tue, 17 Nov 2020 09:49:49 +0100 [thread overview]
Message-ID: <0b429c41-421a-2ae0-66a0-a142c56acadd@baylibre.com> (raw)
In-Reply-To: <20201116200744.495826-1-maz@kernel.org>
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(-)
>
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next prev parent reply other threads:[~2020-11-17 8:49 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-16 20:07 [PATCH 0/4] drm/meson: Module removal fixes Marc Zyngier
2020-11-16 20:07 ` [PATCH 1/4] drm/meson: Free RDMA resources after tearing down DRM Marc Zyngier
2020-11-17 8:51 ` Neil Armstrong
2020-11-16 20:07 ` [PATCH 2/4] drm/meson: Unbind all connectors on module removal Marc Zyngier
2020-11-17 8:53 ` Neil Armstrong
2020-11-16 20:07 ` [PATCH 3/4] drm/meson: dw-hdmi: Register a callback to disable the regulator Marc Zyngier
2020-11-17 8:55 ` Neil Armstrong
2020-11-16 20:07 ` [PATCH 4/4] drm/meson: dw-hdmi: Ensure that clocks are enabled before touching the TOP registers Marc Zyngier
2020-11-17 8:56 ` Neil Armstrong
2020-11-17 8:49 ` Neil Armstrong [this message]
2020-11-17 9:19 ` [PATCH 0/4] drm/meson: Module removal fixes Marc Zyngier
2020-11-17 9:46 ` Neil Armstrong
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