On Thursday, September 10, 2015 12:19:03 PM Thierry Reding wrote:
> From: Thierry Reding <tred...@nvidia.com>
>
> Deferred probe can lead to strange situations where a device that is a
> dependency for others will be moved to the end of the dpm_list. At the
> same time the dependers may not be moved because at the time they will
> be probed the dependee may already have been successfully reprobed and
> they will not have to defer the probe themselves.
So there's a bug in the implementation of deferred probing IMO.
> One example where this happens is the Jetson TK1 board (Tegra124). The
> gpio-keys driver exposes the power key of the board as an input device
> that can also be used as a wakeup source. Commit 17cdddf0fb68 ("ARM:
> tegra: Add gpio-ranges property") results in the gpio-tegra driver
> deferring probe because one of its dependencies, the pinctrl-tegra
> driver, has not successfully completed probing. Currently the deferred
> probe code will move the corresponding gpio-tegra device to the end of
> the dpm_list, but by the time the gpio-keys device, depending on the
> gpio-tegra device, is probed, gpio-tegra has already been reprobed, so
> the gpio-keys device is not moved to the end of dpm_list itself. As a
> result, the suspend ordering becomes pinctrl-tegra -> gpio-keys ->
> gpio-tegra. That's problematic because the gpio-keys driver requests
> the power key to be a wakeup source. However, the programming of the
> wakeup interrupt registers happens in the gpio-tegra driver's suspend
> callback, which is now called before that of the gpio-keys driver. The
> result is that the wrong values are programmed and leaves the system
> unable to be resumed using the power key.
>
> To fix this situation, always move devices to the end of the dpm_list
> before probing them. Technically this should only be done for devices
> that have been successfully probed, but that won't work for recursive
> probing of devices (think an I2C master that instantiates children in
> its ->probe()). Effectively the dpm_list will end up ordered the same
> way that devices were probed, hence taking care of dependencies.
>
> Signed-off-by: Thierry Reding <tred...@nvidia.com>
> ---
> Note that this commit is kind of the PM equivalent of 52cdbdd49853
> ("driver core: correct device's shutdown order) and that we have two
> lists that are essentially the same (dpm_list and devices_kset). I'm
> wondering if it would be worth looking into getting rid of one of
> them? I don't see any reason why the ordering for shutdown and
> suspend/resume should be different, and having a single list would
> help keep this in sync.
We move away things from dpm_list during suspend and add them back to it
during resume to handle the situations in which some devices go away or
appear during suspend/resume. That makes this idea potentially problematic.
>
> drivers/base/dd.c | 33 +++++++++++++++++++++++----------
> 1 file changed, 23 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> index be0eb4639128..56291b11049b 100644
> --- a/drivers/base/dd.c
> +++ b/drivers/base/dd.c
> @@ -88,16 +88,6 @@ static void deferred_probe_work_func(struct work_struct
> *work)
> */
> mutex_unlock(&deferred_probe_mutex);
>
> - /*
> - * Force the device to the end of the dpm_list since
> - * the PM code assumes that the order we add things to
> - * the list is a good order for suspend but deferred
> - * probe makes that very unsafe.
> - */
> - device_pm_lock();
> - device_pm_move_last(dev);
> - device_pm_unlock();
> -
> dev_dbg(dev, "Retrying from deferred list\n");
> bus_probe_device(dev);
>
> @@ -312,6 +302,29 @@ static int really_probe(struct device *dev, struct
> device_driver *drv)
> */
> devices_kset_move_last(dev);
>
> + /*
> + * Force the device to the end of the dpm_list since the PM code
> + * assumes that the order we add things to the list is a good order
> + * for suspend but deferred probe makes that very unsafe.
> + *
> + * Deferred probe can also cause situations in which a device that is
> + * a dependency for others gets moved further down the dpm_list as a
> + * result of probe deferral. In that case the dependee will end up
> + * getting suspended before any of its dependers.
> + *
> + * To ensure proper ordering of suspend/resume, move every device that
> + * is being probed to the end of the dpm_list. Note that technically
> + * only successfully probed devices need to be moved, but that breaks
> + * for recursively added devices because they would end up in the list
> + * in reverse of the desired order, so we simply do it unconditionally
> + * for all devices before they are being probed. In the worst case the
> + * list will be reordered a couple more times than necessary, which
> + * should be an insignificant amount of work.
> + */
> + device_pm_lock();
> + device_pm_move_last(dev);
> + device_pm_unlock();
So I don't agree with doing that for every driver being probed against the
same device. That's just wasteful IMO.
> +
> if (dev->bus->probe) {
> ret = dev->bus->probe(dev);
> if (ret)
>
Alan, what do you think about this?
Thanks,
Rafael
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