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Fri, 14 Feb 2020 10:39:46 -0500 (EST) Date: Fri, 14 Feb 2020 16:39:45 +0100 From: Maxime Ripard To: Samuel Holland Subject: Re: [PATCH 4/4] drm/sun4i: dsi: Remove incorrect use of runtime PM Message-ID: <20200214153945.f5z42fovcitvdlcr@gilmour.lan> References: <20200211072858.30784-1-samuel@sholland.org> <20200211072858.30784-4-samuel@sholland.org> MIME-Version: 1.0 In-Reply-To: <20200211072858.30784-4-samuel@sholland.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200214_073951_097638_2D367F7F X-CRM114-Status: GOOD ( 23.81 ) 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: David Airlie , linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org, Chen-Yu Tsai , stable@vger.kernel.org, Daniel Vetter , linux-arm-kernel@lists.infradead.org Content-Type: multipart/mixed; boundary="===============8204325303167151396==" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org --===============8204325303167151396== Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="rtmrzd3owfcaeil6" Content-Disposition: inline --rtmrzd3owfcaeil6 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On Tue, Feb 11, 2020 at 01:28:58AM -0600, Samuel Holland wrote: > The driver currently uses runtime PM to perform some of the module > initialization and cleanup. This has three problems: > > 1) There is no Kconfig dependency on CONFIG_PM, so if runtime PM is > disabled, the driver will not work at all, since the module will > never be initialized. > > 2) The driver does not ensure that the device is suspended when > sun6i_dsi_probe() fails or when sun6i_dsi_remove() is called. It > simply disables runtime PM. From the docs of pm_runtime_disable(): > > The device can be either active or suspended after its runtime PM > has been disabled. > > And indeed, the device will likely still be active if sun6i_dsi_probe > fails. For example, if the panel driver is not yet loaded, we have > the following sequence: > > sun6i_dsi_probe() > pm_runtime_enable() > mipi_dsi_host_register() > of_mipi_dsi_device_add(child) > ...device_add()... > __device_attach() > pm_runtime_get_sync(dev->parent) -> Causes resume > bus_for_each_drv() > __device_attach_driver() -> No match for panel > pm_runtime_put(dev->parent) -> Async idle request > component_add() > __component_add() > try_to_bring_up_masters() > try_to_bring_up_master() > sun4i_drv_bind() > component_bind_all() > component_bind() > sun6i_dsi_bind() -> Fails with -EPROBE_DEFER > mipi_dsi_host_unregister() > pm_runtime_disable() > __pm_runtime_disable() > __pm_runtime_barrier() -> Idle request is still pending > cancel_work_sync() -> DSI host is *not* suspended! > > Since the device is not suspended, the clock and regulator are never > disabled. The imbalance causes a WARN at devres free time. > > 3) The driver relies on being suspended when sun6i_dsi_encoder_enable() > is called. The resume callback has a comment that says: > > Some part of it can only be done once we get a number of > lanes, see sun6i_dsi_inst_init > > And then part of the resume callback only runs if dsi->device is not > NULL (that is, if sun6i_dsi_attach() has been called). However, as > the above call graph shows, the resume callback is guaranteed to be > called before sun6i_dsi_attach(); it is called before child devices > get their drivers attached. > > Therefore, part of the controller initialization will only run if the > device is suspended between the calls to mipi_dsi_host_register() and > component_add() (which ends up calling sun6i_dsi_encoder_enable()). > Again, as shown by the above call graph, this is not the case. It > appears that the controller happens to work because it is still > initialized by the bootloader. > > Because the connector is hardcoded to always be connected, the > device's runtime PM reference is not dropped until system suspend, > when sun4i_drv_drm_sys_suspend() ends up calling > sun6i_dsi_encoder_disable(). However, that is done as a system sleep > PM hook, and at that point the system PM core has already taken > another runtime PM reference, so sun6i_dsi_runtime_suspend() is > not called. Likewise, by the time the PM core releases its reference, > sun4i_drv_drm_sys_resume() has already re-enabled the encoder. > > So after system suspend and resume, we have *still never called* > sun6i_dsi_inst_init(), and now that the rest of the display pipeline > has been reset, the DSI host is unable to communicate with the panel, > causing VBLANK timeouts. > > Fix all of these issues by inlining the runtime PM hooks into the > encoder enable/disable functions, which are guaranteed to run after a > panel is attached. This allows sun6i_dsi_inst_init() to be called > unconditionally. Furthermore, this causes the hardware to be turned off > during system suspend and reinitialized on resume, which was not > happening before. > > Fixes: 133add5b5ad4 ("drm/sun4i: Add Allwinner A31 MIPI-DSI controller support") > Signed-off-by: Samuel Holland Applied all 4 patches. This one failed to apply for some reason (even though the context looks similar) so I fixed the conflict by hand, you might want to double check. Thanks! Maxime --rtmrzd3owfcaeil6 Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQRcEzekXsqa64kGDp7j7w1vZxhRxQUCXka/QQAKCRDj7w1vZxhR xROhAP9xJDyQFSRI0tejwko7eZz6nzw0YOPs5uKx1NWyOEkIhAD/cUcrgex7M7Gq jRQ9ouveV4eRA7LCI3o94CXtO5B3kwY= =2318 -----END PGP SIGNATURE----- --rtmrzd3owfcaeil6-- --===============8204325303167151396== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel --===============8204325303167151396==--