| Message ID | 20220517220816.1635044-2-tansuresh@google.com (mailing list archive) |
|---|---|
| State | Handled Elsewhere |
| Headers | show |
| Series | Asynchronous shutdown interface and example implementation | expand |
On Wed, May 18, 2022 at 12:08 AM Tanjore Suresh <tansuresh@google.com> wrote: > > This changes the bus driver interface with additional entry points > to enable devices to implement asynchronous shutdown. The existing > synchronous interface to shutdown is unmodified and retained for > backward compatibility. > > This changes the common device shutdown code to enable devices to > participate in asynchronous shutdown implementation. > > Signed-off-by: Tanjore Suresh <tansuresh@google.com> > --- > drivers/base/core.c | 38 +++++++++++++++++++++++++++++++++++++- > include/linux/device/bus.h | 12 ++++++++++++ > 2 files changed, 49 insertions(+), 1 deletion(-) > > diff --git a/drivers/base/core.c b/drivers/base/core.c > index 3d6430eb0c6a..ba267ae70a22 100644 > --- a/drivers/base/core.c > +++ b/drivers/base/core.c > @@ -4479,6 +4479,7 @@ EXPORT_SYMBOL_GPL(device_change_owner); > void device_shutdown(void) > { > struct device *dev, *parent; > + LIST_HEAD(async_shutdown_list); > > wait_for_device_probe(); > device_block_probing(); > @@ -4523,7 +4524,13 @@ void device_shutdown(void) > dev_info(dev, "shutdown_pre\n"); > dev->class->shutdown_pre(dev); > } > - if (dev->bus && dev->bus->shutdown) { > + if (dev->bus && dev->bus->async_shutdown_start) { > + if (initcall_debug) > + dev_info(dev, "async_shutdown_start\n"); > + dev->bus->async_shutdown_start(dev); > + list_add_tail(&dev->kobj.entry, > + &async_shutdown_list); > + } else if (dev->bus && dev->bus->shutdown) { > if (initcall_debug) > dev_info(dev, "shutdown\n"); > dev->bus->shutdown(dev); > @@ -4543,6 +4550,35 @@ void device_shutdown(void) > spin_lock(&devices_kset->list_lock); > } > spin_unlock(&devices_kset->list_lock); > + > + /* > + * Second pass spin for only devices, that have configured > + * Asynchronous shutdown. > + */ > + while (!list_empty(&async_shutdown_list)) { > + dev = list_entry(async_shutdown_list.next, struct device, > + kobj.entry); > + parent = get_device(dev->parent); > + get_device(dev); > + /* > + * Make sure the device is off the list > + */ > + list_del_init(&dev->kobj.entry); > + if (parent) > + device_lock(parent); > + device_lock(dev); > + if (dev->bus && dev->bus->async_shutdown_end) { > + if (initcall_debug) > + dev_info(dev, > + "async_shutdown_end called\n"); > + dev->bus->async_shutdown_end(dev); > + } > + device_unlock(dev); > + if (parent) > + device_unlock(parent); > + put_device(dev); > + put_device(parent); > + } > } > > /* > diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h > index a039ab809753..f582c9d21515 100644 > --- a/include/linux/device/bus.h > +++ b/include/linux/device/bus.h > @@ -49,6 +49,16 @@ struct fwnode_handle; > * will never get called until they do. > * @remove: Called when a device removed from this bus. > * @shutdown: Called at shut-down time to quiesce the device. > + * @async_shutdown_start: Called at the shutdown-time to start > + * the shutdown process on the device. > + * This entry point will be called only > + * when the bus driver has indicated it would > + * like to participate in asynchronous shutdown > + * completion. > + * @async_shutdown_end: Called at shutdown-time to complete the shutdown > + * process of the device. This entry point will be called > + * only when the bus drive has indicated it would like to > + * participate in the asynchronous shutdown completion. I'm going to repeat my point here, but only once. I see no reason to do async shutdown this way, instead of adding a flag for drivers to opt in for calling their existing shutdown callbacks asynchronously, in analogy with the async suspend and resume implementation. Is there any reason why this is not viable? > * > * @online: Called to put the device back online (after offlining it). > * @offline: Called to put the device offline for hot-removal. May fail. > @@ -93,6 +103,8 @@ struct bus_type { > void (*sync_state)(struct device *dev); > void (*remove)(struct device *dev); > void (*shutdown)(struct device *dev); > + void (*async_shutdown_start)(struct device *dev); > + void (*async_shutdown_end)(struct device *dev); > > int (*online)(struct device *dev); > int (*offline)(struct device *dev); > -- > 2.36.0.550.gb090851708-goog >
On Wed, May 18, 2022 at 01:38:49PM +0200, Rafael J. Wysocki wrote: > On Wed, May 18, 2022 at 12:08 AM Tanjore Suresh <tansuresh@google.com> wrote: > > > > This changes the bus driver interface with additional entry points > > to enable devices to implement asynchronous shutdown. The existing > > synchronous interface to shutdown is unmodified and retained for > > backward compatibility. > > > > This changes the common device shutdown code to enable devices to > > participate in asynchronous shutdown implementation. > > > > Signed-off-by: Tanjore Suresh <tansuresh@google.com> > > --- > > drivers/base/core.c | 38 +++++++++++++++++++++++++++++++++++++- > > include/linux/device/bus.h | 12 ++++++++++++ > > 2 files changed, 49 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/base/core.c b/drivers/base/core.c > > index 3d6430eb0c6a..ba267ae70a22 100644 > > --- a/drivers/base/core.c > > +++ b/drivers/base/core.c > > @@ -4479,6 +4479,7 @@ EXPORT_SYMBOL_GPL(device_change_owner); > > void device_shutdown(void) > > { > > struct device *dev, *parent; > > + LIST_HEAD(async_shutdown_list); > > > > wait_for_device_probe(); > > device_block_probing(); > > @@ -4523,7 +4524,13 @@ void device_shutdown(void) > > dev_info(dev, "shutdown_pre\n"); > > dev->class->shutdown_pre(dev); > > } > > - if (dev->bus && dev->bus->shutdown) { > > + if (dev->bus && dev->bus->async_shutdown_start) { > > + if (initcall_debug) > > + dev_info(dev, "async_shutdown_start\n"); > > + dev->bus->async_shutdown_start(dev); > > + list_add_tail(&dev->kobj.entry, > > + &async_shutdown_list); > > + } else if (dev->bus && dev->bus->shutdown) { > > if (initcall_debug) > > dev_info(dev, "shutdown\n"); > > dev->bus->shutdown(dev); > > @@ -4543,6 +4550,35 @@ void device_shutdown(void) > > spin_lock(&devices_kset->list_lock); > > } > > spin_unlock(&devices_kset->list_lock); > > + > > + /* > > + * Second pass spin for only devices, that have configured > > + * Asynchronous shutdown. > > + */ > > + while (!list_empty(&async_shutdown_list)) { > > + dev = list_entry(async_shutdown_list.next, struct device, > > + kobj.entry); > > + parent = get_device(dev->parent); > > + get_device(dev); > > + /* > > + * Make sure the device is off the list > > + */ > > + list_del_init(&dev->kobj.entry); > > + if (parent) > > + device_lock(parent); > > + device_lock(dev); > > + if (dev->bus && dev->bus->async_shutdown_end) { > > + if (initcall_debug) > > + dev_info(dev, > > + "async_shutdown_end called\n"); > > + dev->bus->async_shutdown_end(dev); > > + } > > + device_unlock(dev); > > + if (parent) > > + device_unlock(parent); > > + put_device(dev); > > + put_device(parent); > > + } > > } > > > > /* > > diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h > > index a039ab809753..f582c9d21515 100644 > > --- a/include/linux/device/bus.h > > +++ b/include/linux/device/bus.h > > @@ -49,6 +49,16 @@ struct fwnode_handle; > > * will never get called until they do. > > * @remove: Called when a device removed from this bus. > > * @shutdown: Called at shut-down time to quiesce the device. > > + * @async_shutdown_start: Called at the shutdown-time to start > > + * the shutdown process on the device. > > + * This entry point will be called only > > + * when the bus driver has indicated it would > > + * like to participate in asynchronous shutdown > > + * completion. > > + * @async_shutdown_end: Called at shutdown-time to complete the shutdown > > + * process of the device. This entry point will be called > > + * only when the bus drive has indicated it would like to > > + * participate in the asynchronous shutdown completion. > > I'm going to repeat my point here, but only once. > > I see no reason to do async shutdown this way, instead of adding a > flag for drivers to opt in for calling their existing shutdown > callbacks asynchronously, in analogy with the async suspend and resume > implementation. There's a lot of code here that mere mortals like myself don't understand very well, so here's my meager understanding of how async suspend works and what you're suggesting to make this a little more concrete. Devices have this async_suspend bit: struct device { struct dev_pm_info { unsigned int async_suspend:1; Drivers call device_enable_async_suspend() to set async_suspend if they want it. The system suspend path is something like this: suspend_enter dpm_suspend_noirq(PMSG_SUSPEND) dpm_noirq_suspend_devices(PMSG_SUSPEND) pm_transition = PMSG_SUSPEND while (!list_empty(&dpm_late_early_list)) device_suspend_noirq(dev) dpm_async_fn(dev, async_suspend_noirq) if (is_async(dev)) async_schedule_dev(async_suspend_noirq) # async path async_suspend_noirq # called asynchronously __device_suspend_noirq(dev, PMSG_SUSPEND, true) callback = pm_noirq_op(PMSG_SUSPEND) # .suspend_noirq() dpm_run_callback(callback) # async call __device_suspend_noirq(dev, pm_transition, false) # sync path callback = pm_noirq_op(PMSG_SUSPEND) # .suspend_noirq() dpm_run_callback(callback) # sync call async_synchronize_full # wait If a driver has called device_enable_async_suspend(), we'll use the async_schedule_dev() path to schedule the appropriate .suspend_noirq() method. After scheduling it via the async path or directly calling it via the sync path, the async_synchronize_full() waits for completion of all the async methods. I assume your suggestion is to do something like this: struct device { struct dev_pm_info { unsigned int async_suspend:1; + unsigned int async_shutdown:1; + void device_enable_async_shutdown(struct device *dev) + dev->power.async_shutdown = true; device_shutdown while (!list_empty(&devices_kset->list)) - dev->...->shutdown() + if (is_async_shutdown(dev)) + async_schedule_dev(async_shutdown) # async path + + async_shutdown # called asynchronously + dev->...->shutdown() + + else + dev->...->shutdown() # sync path + + async_synchronize_full # wait
On Wed, May 18, 2022 at 7:50 PM Bjorn Helgaas <helgaas@kernel.org> wrote: > > On Wed, May 18, 2022 at 01:38:49PM +0200, Rafael J. Wysocki wrote: > > On Wed, May 18, 2022 at 12:08 AM Tanjore Suresh <tansuresh@google.com> wrote: > > > > > > This changes the bus driver interface with additional entry points > > > to enable devices to implement asynchronous shutdown. The existing > > > synchronous interface to shutdown is unmodified and retained for > > > backward compatibility. > > > > > > This changes the common device shutdown code to enable devices to > > > participate in asynchronous shutdown implementation. > > > > > > Signed-off-by: Tanjore Suresh <tansuresh@google.com> > > > --- > > > drivers/base/core.c | 38 +++++++++++++++++++++++++++++++++++++- > > > include/linux/device/bus.h | 12 ++++++++++++ > > > 2 files changed, 49 insertions(+), 1 deletion(-) > > > > > > diff --git a/drivers/base/core.c b/drivers/base/core.c > > > index 3d6430eb0c6a..ba267ae70a22 100644 > > > --- a/drivers/base/core.c > > > +++ b/drivers/base/core.c > > > @@ -4479,6 +4479,7 @@ EXPORT_SYMBOL_GPL(device_change_owner); > > > void device_shutdown(void) > > > { > > > struct device *dev, *parent; > > > + LIST_HEAD(async_shutdown_list); > > > > > > wait_for_device_probe(); > > > device_block_probing(); > > > @@ -4523,7 +4524,13 @@ void device_shutdown(void) > > > dev_info(dev, "shutdown_pre\n"); > > > dev->class->shutdown_pre(dev); > > > } > > > - if (dev->bus && dev->bus->shutdown) { > > > + if (dev->bus && dev->bus->async_shutdown_start) { > > > + if (initcall_debug) > > > + dev_info(dev, "async_shutdown_start\n"); > > > + dev->bus->async_shutdown_start(dev); > > > + list_add_tail(&dev->kobj.entry, > > > + &async_shutdown_list); > > > + } else if (dev->bus && dev->bus->shutdown) { > > > if (initcall_debug) > > > dev_info(dev, "shutdown\n"); > > > dev->bus->shutdown(dev); > > > @@ -4543,6 +4550,35 @@ void device_shutdown(void) > > > spin_lock(&devices_kset->list_lock); > > > } > > > spin_unlock(&devices_kset->list_lock); > > > + > > > + /* > > > + * Second pass spin for only devices, that have configured > > > + * Asynchronous shutdown. > > > + */ > > > + while (!list_empty(&async_shutdown_list)) { > > > + dev = list_entry(async_shutdown_list.next, struct device, > > > + kobj.entry); > > > + parent = get_device(dev->parent); > > > + get_device(dev); > > > + /* > > > + * Make sure the device is off the list > > > + */ > > > + list_del_init(&dev->kobj.entry); > > > + if (parent) > > > + device_lock(parent); > > > + device_lock(dev); > > > + if (dev->bus && dev->bus->async_shutdown_end) { > > > + if (initcall_debug) > > > + dev_info(dev, > > > + "async_shutdown_end called\n"); > > > + dev->bus->async_shutdown_end(dev); > > > + } > > > + device_unlock(dev); > > > + if (parent) > > > + device_unlock(parent); > > > + put_device(dev); > > > + put_device(parent); > > > + } > > > } > > > > > > /* > > > diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h > > > index a039ab809753..f582c9d21515 100644 > > > --- a/include/linux/device/bus.h > > > +++ b/include/linux/device/bus.h > > > @@ -49,6 +49,16 @@ struct fwnode_handle; > > > * will never get called until they do. > > > * @remove: Called when a device removed from this bus. > > > * @shutdown: Called at shut-down time to quiesce the device. > > > + * @async_shutdown_start: Called at the shutdown-time to start > > > + * the shutdown process on the device. > > > + * This entry point will be called only > > > + * when the bus driver has indicated it would > > > + * like to participate in asynchronous shutdown > > > + * completion. > > > + * @async_shutdown_end: Called at shutdown-time to complete the shutdown > > > + * process of the device. This entry point will be called > > > + * only when the bus drive has indicated it would like to > > > + * participate in the asynchronous shutdown completion. > > > > I'm going to repeat my point here, but only once. > > > > I see no reason to do async shutdown this way, instead of adding a > > flag for drivers to opt in for calling their existing shutdown > > callbacks asynchronously, in analogy with the async suspend and resume > > implementation. > > There's a lot of code here that mere mortals like myself don't > understand very well, so here's my meager understanding of how > async suspend works and what you're suggesting to make this a > little more concrete. > > Devices have this async_suspend bit: > > struct device { > struct dev_pm_info { > unsigned int async_suspend:1; > > Drivers call device_enable_async_suspend() to set async_suspend if > they want it. The system suspend path is something like this: > > suspend_enter > dpm_suspend_noirq(PMSG_SUSPEND) > dpm_noirq_suspend_devices(PMSG_SUSPEND) > pm_transition = PMSG_SUSPEND > while (!list_empty(&dpm_late_early_list)) > device_suspend_noirq(dev) > dpm_async_fn(dev, async_suspend_noirq) > if (is_async(dev)) > async_schedule_dev(async_suspend_noirq) # async path > > async_suspend_noirq # called asynchronously > __device_suspend_noirq(dev, PMSG_SUSPEND, true) > callback = pm_noirq_op(PMSG_SUSPEND) # .suspend_noirq() > dpm_run_callback(callback) # async call > > __device_suspend_noirq(dev, pm_transition, false) # sync path > callback = pm_noirq_op(PMSG_SUSPEND) # .suspend_noirq() > dpm_run_callback(callback) # sync call > > async_synchronize_full # wait > > If a driver has called device_enable_async_suspend(), we'll use the > async_schedule_dev() path to schedule the appropriate .suspend_noirq() > method. After scheduling it via the async path or directly calling it > via the sync path, the async_synchronize_full() waits for completion > of all the async methods. > > I assume your suggestion is to do something like this: > > struct device { > struct dev_pm_info { > unsigned int async_suspend:1; > + unsigned int async_shutdown:1; > > + void device_enable_async_shutdown(struct device *dev) > + dev->power.async_shutdown = true; > > device_shutdown > while (!list_empty(&devices_kset->list)) > - dev->...->shutdown() > + if (is_async_shutdown(dev)) > + async_schedule_dev(async_shutdown) # async path > + > + async_shutdown # called asynchronously > + dev->...->shutdown() > + > + else > + dev->...->shutdown() # sync path > + > + async_synchronize_full # wait Yes, that's the idea IIUC.
Rafeal, On Wed, May 18, 2022 at 11:01 AM Rafael J. Wysocki <rafael@kernel.org> wrote: > > On Wed, May 18, 2022 at 7:50 PM Bjorn Helgaas <helgaas@kernel.org> wrote: > > > > On Wed, May 18, 2022 at 01:38:49PM +0200, Rafael J. Wysocki wrote: > > > On Wed, May 18, 2022 at 12:08 AM Tanjore Suresh <tansuresh@google.com> wrote: > > > > > > > > This changes the bus driver interface with additional entry points > > > > to enable devices to implement asynchronous shutdown. The existing > > > > synchronous interface to shutdown is unmodified and retained for > > > > backward compatibility. > > > > > > > > This changes the common device shutdown code to enable devices to > > > > participate in asynchronous shutdown implementation. > > > > > > > > Signed-off-by: Tanjore Suresh <tansuresh@google.com> > > > > --- > > > > drivers/base/core.c | 38 +++++++++++++++++++++++++++++++++++++- > > > > include/linux/device/bus.h | 12 ++++++++++++ > > > > 2 files changed, 49 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/base/core.c b/drivers/base/core.c > > > > index 3d6430eb0c6a..ba267ae70a22 100644 > > > > --- a/drivers/base/core.c > > > > +++ b/drivers/base/core.c > > > > @@ -4479,6 +4479,7 @@ EXPORT_SYMBOL_GPL(device_change_owner); > > > > void device_shutdown(void) > > > > { > > > > struct device *dev, *parent; > > > > + LIST_HEAD(async_shutdown_list); > > > > > > > > wait_for_device_probe(); > > > > device_block_probing(); > > > > @@ -4523,7 +4524,13 @@ void device_shutdown(void) > > > > dev_info(dev, "shutdown_pre\n"); > > > > dev->class->shutdown_pre(dev); > > > > } > > > > - if (dev->bus && dev->bus->shutdown) { > > > > + if (dev->bus && dev->bus->async_shutdown_start) { > > > > + if (initcall_debug) > > > > + dev_info(dev, "async_shutdown_start\n"); > > > > + dev->bus->async_shutdown_start(dev); > > > > + list_add_tail(&dev->kobj.entry, > > > > + &async_shutdown_list); > > > > + } else if (dev->bus && dev->bus->shutdown) { > > > > if (initcall_debug) > > > > dev_info(dev, "shutdown\n"); > > > > dev->bus->shutdown(dev); > > > > @@ -4543,6 +4550,35 @@ void device_shutdown(void) > > > > spin_lock(&devices_kset->list_lock); > > > > } > > > > spin_unlock(&devices_kset->list_lock); > > > > + > > > > + /* > > > > + * Second pass spin for only devices, that have configured > > > > + * Asynchronous shutdown. > > > > + */ > > > > + while (!list_empty(&async_shutdown_list)) { > > > > + dev = list_entry(async_shutdown_list.next, struct device, > > > > + kobj.entry); > > > > + parent = get_device(dev->parent); > > > > + get_device(dev); > > > > + /* > > > > + * Make sure the device is off the list > > > > + */ > > > > + list_del_init(&dev->kobj.entry); > > > > + if (parent) > > > > + device_lock(parent); > > > > + device_lock(dev); > > > > + if (dev->bus && dev->bus->async_shutdown_end) { > > > > + if (initcall_debug) > > > > + dev_info(dev, > > > > + "async_shutdown_end called\n"); > > > > + dev->bus->async_shutdown_end(dev); > > > > + } > > > > + device_unlock(dev); > > > > + if (parent) > > > > + device_unlock(parent); > > > > + put_device(dev); > > > > + put_device(parent); > > > > + } > > > > } > > > > > > > > /* > > > > diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h > > > > index a039ab809753..f582c9d21515 100644 > > > > --- a/include/linux/device/bus.h > > > > +++ b/include/linux/device/bus.h > > > > @@ -49,6 +49,16 @@ struct fwnode_handle; > > > > * will never get called until they do. > > > > * @remove: Called when a device removed from this bus. > > > > * @shutdown: Called at shut-down time to quiesce the device. > > > > + * @async_shutdown_start: Called at the shutdown-time to start > > > > + * the shutdown process on the device. > > > > + * This entry point will be called only > > > > + * when the bus driver has indicated it would > > > > + * like to participate in asynchronous shutdown > > > > + * completion. > > > > + * @async_shutdown_end: Called at shutdown-time to complete the shutdown > > > > + * process of the device. This entry point will be called > > > > + * only when the bus drive has indicated it would like to > > > > + * participate in the asynchronous shutdown completion. > > > > > > I'm going to repeat my point here, but only once. > > > > > > I see no reason to do async shutdown this way, instead of adding a > > > flag for drivers to opt in for calling their existing shutdown > > > callbacks asynchronously, in analogy with the async suspend and resume > > > implementation. > > > > There's a lot of code here that mere mortals like myself don't > > understand very well, so here's my meager understanding of how > > async suspend works and what you're suggesting to make this a > > little more concrete. > > > > Devices have this async_suspend bit: > > > > struct device { > > struct dev_pm_info { > > unsigned int async_suspend:1; > > > > Drivers call device_enable_async_suspend() to set async_suspend if > > they want it. The system suspend path is something like this: > > > > suspend_enter > > dpm_suspend_noirq(PMSG_SUSPEND) > > dpm_noirq_suspend_devices(PMSG_SUSPEND) > > pm_transition = PMSG_SUSPEND > > while (!list_empty(&dpm_late_early_list)) > > device_suspend_noirq(dev) > > dpm_async_fn(dev, async_suspend_noirq) > > if (is_async(dev)) > > async_schedule_dev(async_suspend_noirq) # async path > > > > async_suspend_noirq # called asynchronously > > __device_suspend_noirq(dev, PMSG_SUSPEND, true) > > callback = pm_noirq_op(PMSG_SUSPEND) # .suspend_noirq() > > dpm_run_callback(callback) # async call > > > > __device_suspend_noirq(dev, pm_transition, false) # sync path > > callback = pm_noirq_op(PMSG_SUSPEND) # .suspend_noirq() > > dpm_run_callback(callback) # sync call > > > > async_synchronize_full # wait > > > > If a driver has called device_enable_async_suspend(), we'll use the > > async_schedule_dev() path to schedule the appropriate .suspend_noirq() > > method. After scheduling it via the async path or directly calling it > > via the sync path, the async_synchronize_full() waits for completion > > of all the async methods. > > > > I assume your suggestion is to do something like this: > > > > struct device { > > struct dev_pm_info { > > unsigned int async_suspend:1; > > + unsigned int async_shutdown:1; > > > > + void device_enable_async_shutdown(struct device *dev) > > + dev->power.async_shutdown = true; > > > > device_shutdown > > while (!list_empty(&devices_kset->list)) > > - dev->...->shutdown() > > + if (is_async_shutdown(dev)) > > + async_schedule_dev(async_shutdown) # async path > > + > > + async_shutdown # called asynchronously > > + dev->...->shutdown() > > + > > + else > > + dev->...->shutdown() # sync path > > + > > + async_synchronize_full # wait > > Yes, that's the idea IIUC. Thanks for the clarification, I misunderstood your earlier comment, thanks for explaining and clarification. Let me evaluate and get back to you as soon as possible. Thanks sureshtk
[Beginning of thread: https://lore.kernel.org/r/20220517220816.1635044-2-tansuresh@google.com] On Wed, May 18, 2022 at 12:50:02PM -0500, Bjorn Helgaas wrote: > Devices have this async_suspend bit: > > struct device { > struct dev_pm_info { > unsigned int async_suspend:1; > > Drivers call device_enable_async_suspend() to set async_suspend if > they want it. The system suspend path is something like this: > > suspend_enter > dpm_suspend_noirq(PMSG_SUSPEND) > dpm_noirq_suspend_devices(PMSG_SUSPEND) > pm_transition = PMSG_SUSPEND > while (!list_empty(&dpm_late_early_list)) > device_suspend_noirq(dev) > dpm_async_fn(dev, async_suspend_noirq) > if (is_async(dev)) > async_schedule_dev(async_suspend_noirq) # async path > > async_suspend_noirq # called asynchronously > __device_suspend_noirq(dev, PMSG_SUSPEND, true) > callback = pm_noirq_op(PMSG_SUSPEND) # .suspend_noirq() > dpm_run_callback(callback) # async call > > __device_suspend_noirq(dev, pm_transition, false) # sync path > callback = pm_noirq_op(PMSG_SUSPEND) # .suspend_noirq() > dpm_run_callback(callback) # sync call > > async_synchronize_full # wait > > If a driver has called device_enable_async_suspend(), we'll use the > async_schedule_dev() path to schedule the appropriate .suspend_noirq() > method. After scheduling it via the async path or directly calling it > via the sync path, the async_synchronize_full() waits for completion > of all the async methods. Correct me if I'm wrong: in the suspend scenario, there are several phases, and async_synchronize_full() ensures that one phase finishes before the next phase starts. For example: dpm_suspend_end dpm_suspend_late # phase 1 while (!list_empty(&dpm_suspended_list)) device_suspend_late async_synchronize_full # finish phase 1 dpm_suspend_noirq # phase 2 dpm_noirq_suspend_devices while (!list_empty(&dpm_late_early_list)) device_suspend_noirq async_synchronize_full The device .suspend_late() and .suspend_noirq() methods may all be started asynchronously. So far there's nothing to order them within the phase, but async_synchronize_full() ensures that all the .suspend_late() methods finish before the .suspend_noirq() methods start. Obviously we do want a child's method to complete before we run the parent's method. If I understand correctly, that parent/child synchronization is done by a different method: __device_suspend_late() and __device_suspend_noirq() call dpm_wait_for_subordinate(), which waits for &dev->power.completion for all children: __device_suspend_late dpm_wait_for_subordinate dpm_wait_for_children # wait for children .suspend_late() device_for_each_child(dev, &async, dpm_wait_fn) dpm_wait_fn dpm_wait wait_for_completion(&dev->power.completion) dpm_run_callback # run parent method, e.g., ops->suspend_late complete_all(&dev->power.completion) # note completion of parent > I assume your suggestion is to do something like this: > > struct device { > struct dev_pm_info { > unsigned int async_suspend:1; > + unsigned int async_shutdown:1; > > + void device_enable_async_shutdown(struct device *dev) > + dev->power.async_shutdown = true; > > device_shutdown > while (!list_empty(&devices_kset->list)) > - dev->...->shutdown() > + if (is_async_shutdown(dev)) > + async_schedule_dev(async_shutdown) # async path > + > + async_shutdown # called asynchronously > + dev->...->shutdown() > + > + else > + dev->...->shutdown() # sync path > + > + async_synchronize_full # wait In the shutdown case, I think we still probably need the async_synchronize_full() to ensure that all the .shutdown() methods complete before we turn the power off, reboot, or kexec. But I think we also need a mechanism like dev->power.completion to make sure all the child .shutdown() methods complete before we run a parent's .shutdown(). There's not much overlap between the suspend path and the shutdown path (probably none at all), so it's tempting to use the existing dev->power.completion for shutdown as well. But I don't think that's feasible because dev->power.completion is tied up with dev->power.async_suspend, which is set by device_enable_async_suspend(). That's a different concept than async shutdown, and drivers will want one without the other. Does this make sense? Bjorn
On Tue, Aug 2, 2022 at 11:35 PM Bjorn Helgaas <helgaas@kernel.org> wrote: > > [Beginning of thread: https://lore.kernel.org/r/20220517220816.1635044-2-tansuresh@google.com] > On Wed, May 18, 2022 at 12:50:02PM -0500, Bjorn Helgaas wrote: > > > Devices have this async_suspend bit: > > > > struct device { > > struct dev_pm_info { > > unsigned int async_suspend:1; > > > > Drivers call device_enable_async_suspend() to set async_suspend if > > they want it. The system suspend path is something like this: > > > > suspend_enter > > dpm_suspend_noirq(PMSG_SUSPEND) > > dpm_noirq_suspend_devices(PMSG_SUSPEND) > > pm_transition = PMSG_SUSPEND > > while (!list_empty(&dpm_late_early_list)) > > device_suspend_noirq(dev) > > dpm_async_fn(dev, async_suspend_noirq) > > if (is_async(dev)) > > async_schedule_dev(async_suspend_noirq) # async path > > > > async_suspend_noirq # called asynchronously > > __device_suspend_noirq(dev, PMSG_SUSPEND, true) > > callback = pm_noirq_op(PMSG_SUSPEND) # .suspend_noirq() > > dpm_run_callback(callback) # async call > > > > __device_suspend_noirq(dev, pm_transition, false) # sync path > > callback = pm_noirq_op(PMSG_SUSPEND) # .suspend_noirq() > > dpm_run_callback(callback) # sync call > > > > async_synchronize_full # wait > > > > If a driver has called device_enable_async_suspend(), we'll use the > > async_schedule_dev() path to schedule the appropriate .suspend_noirq() > > method. After scheduling it via the async path or directly calling it > > via the sync path, the async_synchronize_full() waits for completion > > of all the async methods. > > Correct me if I'm wrong: in the suspend scenario, there are several > phases, and async_synchronize_full() ensures that one phase finishes > before the next phase starts. For example: > > dpm_suspend_end > dpm_suspend_late # phase 1 > while (!list_empty(&dpm_suspended_list)) > device_suspend_late > async_synchronize_full # finish phase 1 > dpm_suspend_noirq # phase 2 > dpm_noirq_suspend_devices > while (!list_empty(&dpm_late_early_list)) > device_suspend_noirq > async_synchronize_full > > The device .suspend_late() and .suspend_noirq() methods may all be > started asynchronously. So far there's nothing to order them within > the phase, but async_synchronize_full() ensures that all the > .suspend_late() methods finish before the .suspend_noirq() methods > start. > > Obviously we do want a child's method to complete before we run the > parent's method. If I understand correctly, that parent/child > synchronization is done by a different method: __device_suspend_late() > and __device_suspend_noirq() call dpm_wait_for_subordinate(), which > waits for &dev->power.completion for all children: > > __device_suspend_late > dpm_wait_for_subordinate > dpm_wait_for_children # wait for children .suspend_late() > device_for_each_child(dev, &async, dpm_wait_fn) > dpm_wait_fn > dpm_wait > wait_for_completion(&dev->power.completion) > dpm_run_callback # run parent method, e.g., ops->suspend_late > complete_all(&dev->power.completion) # note completion of parent > > > I assume your suggestion is to do something like this: > > > > struct device { > > struct dev_pm_info { > > unsigned int async_suspend:1; > > + unsigned int async_shutdown:1; > > > > + void device_enable_async_shutdown(struct device *dev) > > + dev->power.async_shutdown = true; > > > > device_shutdown > > while (!list_empty(&devices_kset->list)) > > - dev->...->shutdown() > > + if (is_async_shutdown(dev)) > > + async_schedule_dev(async_shutdown) # async path > > + > > + async_shutdown # called asynchronously > > + dev->...->shutdown() > > + > > + else > > + dev->...->shutdown() # sync path > > + > > + async_synchronize_full # wait > > In the shutdown case, I think we still probably need the > async_synchronize_full() to ensure that all the .shutdown() methods > complete before we turn the power off, reboot, or kexec. > > But I think we also need a mechanism like dev->power.completion to > make sure all the child .shutdown() methods complete before we run a > parent's .shutdown(). > > There's not much overlap between the suspend path and the shutdown > path (probably none at all), so it's tempting to use the existing > dev->power.completion for shutdown as well. > > But I don't think that's feasible because dev->power.completion is > tied up with dev->power.async_suspend, which is set by > device_enable_async_suspend(). That's a different concept than async > shutdown, and drivers will want one without the other. > > Does this make sense? Well, why don't we change the code so that dev->power.completion is not tied to dev->power.async_suspend, but can be also used (analogously) if something like dev->async_shutdown is set? My point is that we know how to suspend devices asynchronously (the fact that there are multiple phases is not that important IMV), so why don't we design the async shutdown analogously?
diff --git a/drivers/base/core.c b/drivers/base/core.c index 3d6430eb0c6a..ba267ae70a22 100644 --- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -4479,6 +4479,7 @@ EXPORT_SYMBOL_GPL(device_change_owner); void device_shutdown(void) { struct device *dev, *parent; + LIST_HEAD(async_shutdown_list); wait_for_device_probe(); device_block_probing(); @@ -4523,7 +4524,13 @@ void device_shutdown(void) dev_info(dev, "shutdown_pre\n"); dev->class->shutdown_pre(dev); } - if (dev->bus && dev->bus->shutdown) { + if (dev->bus && dev->bus->async_shutdown_start) { + if (initcall_debug) + dev_info(dev, "async_shutdown_start\n"); + dev->bus->async_shutdown_start(dev); + list_add_tail(&dev->kobj.entry, + &async_shutdown_list); + } else if (dev->bus && dev->bus->shutdown) { if (initcall_debug) dev_info(dev, "shutdown\n"); dev->bus->shutdown(dev); @@ -4543,6 +4550,35 @@ void device_shutdown(void) spin_lock(&devices_kset->list_lock); } spin_unlock(&devices_kset->list_lock); + + /* + * Second pass spin for only devices, that have configured + * Asynchronous shutdown. + */ + while (!list_empty(&async_shutdown_list)) { + dev = list_entry(async_shutdown_list.next, struct device, + kobj.entry); + parent = get_device(dev->parent); + get_device(dev); + /* + * Make sure the device is off the list + */ + list_del_init(&dev->kobj.entry); + if (parent) + device_lock(parent); + device_lock(dev); + if (dev->bus && dev->bus->async_shutdown_end) { + if (initcall_debug) + dev_info(dev, + "async_shutdown_end called\n"); + dev->bus->async_shutdown_end(dev); + } + device_unlock(dev); + if (parent) + device_unlock(parent); + put_device(dev); + put_device(parent); + } } /* diff --git a/include/linux/device/bus.h b/include/linux/device/bus.h index a039ab809753..f582c9d21515 100644 --- a/include/linux/device/bus.h +++ b/include/linux/device/bus.h @@ -49,6 +49,16 @@ struct fwnode_handle; * will never get called until they do. * @remove: Called when a device removed from this bus. * @shutdown: Called at shut-down time to quiesce the device. + * @async_shutdown_start: Called at the shutdown-time to start + * the shutdown process on the device. + * This entry point will be called only + * when the bus driver has indicated it would + * like to participate in asynchronous shutdown + * completion. + * @async_shutdown_end: Called at shutdown-time to complete the shutdown + * process of the device. This entry point will be called + * only when the bus drive has indicated it would like to + * participate in the asynchronous shutdown completion. * * @online: Called to put the device back online (after offlining it). * @offline: Called to put the device offline for hot-removal. May fail. @@ -93,6 +103,8 @@ struct bus_type { void (*sync_state)(struct device *dev); void (*remove)(struct device *dev); void (*shutdown)(struct device *dev); + void (*async_shutdown_start)(struct device *dev); + void (*async_shutdown_end)(struct device *dev); int (*online)(struct device *dev); int (*offline)(struct device *dev);
This changes the bus driver interface with additional entry points to enable devices to implement asynchronous shutdown. The existing synchronous interface to shutdown is unmodified and retained for backward compatibility. This changes the common device shutdown code to enable devices to participate in asynchronous shutdown implementation. Signed-off-by: Tanjore Suresh <tansuresh@google.com> --- drivers/base/core.c | 38 +++++++++++++++++++++++++++++++++++++- include/linux/device/bus.h | 12 ++++++++++++ 2 files changed, 49 insertions(+), 1 deletion(-)