Hi, 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. That's fairly easy to fix. > 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. That's interesting. I guess this is shown when you have the panel as a module? There's something pretty weird though. The comment in __pm_runtime_disable states that it will "wait for all operations in progress to complete" so at the end of __pm_runtime_disable call, the DSI host will be suspended and we shouldn't have a WARN at all. > 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. Isn't it something that has been changed by your previous patch though? > 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. We don't have any bootloader support for MIPI-DSI, so no, that's not it. > 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. Either way, I guess just moving the pm_runtime_enable call to sun6i_dsi_attach will fix this, right? We don't really need to have the DSI controller powered up before that time anyway. > 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. That's not something we should do really. We're really lacking any power management, so we should be having more of runtime_pm, not less. Maxime
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