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Mon, 16 Nov 2020 20:08:11 +0000 From: Marc Zyngier To: Neil Armstrong , Kevin Hilman Subject: [PATCH 0/4] drm/meson: Module removal fixes Date: Mon, 16 Nov 2020 20:07:40 +0000 Message-Id: <20201116200744.495826-1-maz@kernel.org> X-Mailer: git-send-email 2.28.0 MIME-Version: 1.0 X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: narmstrong@baylibre.com, khilman@baylibre.com, jbrunet@baylibre.com, martin.blumenstingl@googlemail.com, kernel-team@android.com, dri-devel@lists.freedesktop.org, linux-amlogic@lists.infradead.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201116_150815_213057_F98FE2F1 X-CRM114-Status: GOOD ( 16.97 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Martin Blumenstingl , 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 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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... 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. I went as far as reaching out for a HDMI cable and verifying that I was getting a working display. Total dedication. 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(-) -- 2.28.0 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel