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SubjectRe: [PATCH 4/4] drm/sun4i: dsi: Remove incorrect use of runtime PM
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.

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