| Message ID | BANLkTi=7cM2dXniHM4mnXs46KaTc05hh-Q@mail.gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Fri, 24 Jun 2011 22:49:56 -0600 Grant Likely <grant.likely@secretlab.ca> wrote: > [cc'ing linux kernel since I discuss driver core issues] > [cc'ing greg and kay, 'cause I've included a patch I'd like you to > look at (see end of email)] > > On Fri, Jun 24, 2011 at 8:10 AM, Marc Zyngier <marc.zyngier@arm.com> wrote: > > Add support for populating early platform devices from the device > > tree, by walking the tree and adding nodes whose 'compatible' > > property matches the 'class' string passed as a parameter. > > > > This allows devices to be probed long before the whole device > > infrastructure is available. > > > > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> > > --- > > drivers/of/platform.c | 26 ++++++++++++++++++++++++++ > > include/linux/of_platform.h | 1 + > > 2 files changed, 27 insertions(+), 0 deletions(-) > > > > diff --git a/drivers/of/platform.c b/drivers/of/platform.c > > index e75af39..2a323ee 100644 > > --- a/drivers/of/platform.c > > +++ b/drivers/of/platform.c > > @@ -458,4 +458,30 @@ int of_platform_populate(struct device_node *root, > > of_node_put(root); > > return rc; > > } > > + > > +/** > > + * of_early_platform_populate() - Populate early platform devices from DT > > + * @class: string to compare to the 'compatible' attributes > > + * > > + * This function walks the device tree and register devices whose > > + * 'compatible' property matches the 'class' parameter. > > + * > > + * Returns 0 on success, < 0 on failure. > > + */ > > +int of_early_platform_populate(const char *class) > > +{ > > + struct platform_device *pdev; > > + struct device_node *np = NULL; > > + > > + while ((np = of_find_compatible_node(np, NULL, class))) { > > for_each_compatible_node() > > > + pdev = of_device_alloc(np, NULL, NULL); > > + if (!pdev) > > + return -ENOMEM; > > + list_del(&pdev->dev.devres_head); > > + memset(&pdev->dev.devres_head, 0, sizeof(pdev->dev.devres_head)); > > + early_platform_add_devices(&pdev, 1); > > I'm not sure this will work reliably. The of_platform semantics are > still slightly different from 'regular' platform devices (which I do > intend to fix though), so it may cause problems with how the device > name gets assigned. I'd need to dig into it though. > > > + } > > + > > + return 0; > > +} > > Hmmm, I'd really rather not go down the path of having different > 'classes' of devices that need to be registered at different times. > There just isn't a really good generic way to know which devices > should be the 'early' ones, it gets hairy with regard to making sure > devices don't get registered twice, and it doesn't actually solve the > problem that there is no way to handle dependencies between devices in > the Linux device model. > > What I /want/ to do is allow drivers to defer initialization at .probe > time if some of the resources it needs aren't yet available. > Unfortunately, that doesn't work so well for interrupt controllers > since irq numbers are expected to be correctly populated in the > platform device resource table. What complicates things further is > that most gpio controllers are doubling as irq controllers nowdays, > and those are typically modelled with platform devices themselves. While I totally agree with all the above, this patch tries to address a slightly different problem. On top of device/device dependencies, there is also a number of implicit dependencies. In the case I'm currently trying to solve, the kernel expects a timer to be up and running when hitting the delay loop calibration. At that stage, it is impossible to register a platform device, hence the use (abuse?) of early platform devices. The current ARM code relies on the timers *not* being a standard device, and being directly setup by an board specific method. The SMP timers are even worse, as they are directly called by the core code, meaning that we can only have *one* implementation at a time in the kernel. So the early platform stuff is a potential solution for that, though there is no way it would handle any kind of dependency. What I dream of is to have the full device/driver infrastructure available much earlier, before the rest of the kernel starts relying on some hardware being up and running... Cheers, M.
On Sat, Jun 25, 2011 at 12:11:42PM +0100, Marc Zyngier wrote: > On Fri, 24 Jun 2011 22:49:56 -0600 > Grant Likely <grant.likely@secretlab.ca> wrote: > > > [cc'ing linux kernel since I discuss driver core issues] > > [cc'ing greg and kay, 'cause I've included a patch I'd like you to > > look at (see end of email)] > > > > On Fri, Jun 24, 2011 at 8:10 AM, Marc Zyngier <marc.zyngier@arm.com> wrote: > > > Add support for populating early platform devices from the device > > > tree, by walking the tree and adding nodes whose 'compatible' > > > property matches the 'class' string passed as a parameter. > > > > > > This allows devices to be probed long before the whole device > > > infrastructure is available. > > > > > > Signed-off-by: Marc Zyngier <marc.zyngier@arm.com> > > > --- > > > drivers/of/platform.c | 26 ++++++++++++++++++++++++++ > > > include/linux/of_platform.h | 1 + > > > 2 files changed, 27 insertions(+), 0 deletions(-) > > > > > > diff --git a/drivers/of/platform.c b/drivers/of/platform.c > > > index e75af39..2a323ee 100644 > > > --- a/drivers/of/platform.c > > > +++ b/drivers/of/platform.c > > > @@ -458,4 +458,30 @@ int of_platform_populate(struct device_node *root, > > > of_node_put(root); > > > return rc; > > > } > > > + > > > +/** > > > + * of_early_platform_populate() - Populate early platform devices from DT > > > + * @class: string to compare to the 'compatible' attributes > > > + * > > > + * This function walks the device tree and register devices whose > > > + * 'compatible' property matches the 'class' parameter. > > > + * > > > + * Returns 0 on success, < 0 on failure. > > > + */ > > > +int of_early_platform_populate(const char *class) > > > +{ > > > + struct platform_device *pdev; > > > + struct device_node *np = NULL; > > > + > > > + while ((np = of_find_compatible_node(np, NULL, class))) { > > > > for_each_compatible_node() > > > > > + pdev = of_device_alloc(np, NULL, NULL); > > > + if (!pdev) > > > + return -ENOMEM; > > > + list_del(&pdev->dev.devres_head); > > > + memset(&pdev->dev.devres_head, 0, sizeof(pdev->dev.devres_head)); > > > + early_platform_add_devices(&pdev, 1); > > > > I'm not sure this will work reliably. The of_platform semantics are > > still slightly different from 'regular' platform devices (which I do > > intend to fix though), so it may cause problems with how the device > > name gets assigned. I'd need to dig into it though. > > > > > + } > > > + > > > + return 0; > > > +} > > > > Hmmm, I'd really rather not go down the path of having different > > 'classes' of devices that need to be registered at different times. > > There just isn't a really good generic way to know which devices > > should be the 'early' ones, it gets hairy with regard to making sure > > devices don't get registered twice, and it doesn't actually solve the > > problem that there is no way to handle dependencies between devices in > > the Linux device model. > > > > What I /want/ to do is allow drivers to defer initialization at .probe > > time if some of the resources it needs aren't yet available. > > Unfortunately, that doesn't work so well for interrupt controllers > > since irq numbers are expected to be correctly populated in the > > platform device resource table. What complicates things further is > > that most gpio controllers are doubling as irq controllers nowdays, > > and those are typically modelled with platform devices themselves. > > While I totally agree with all the above, this patch tries to address a > slightly different problem. On top of device/device dependencies, there > is also a number of implicit dependencies. > > In the case I'm currently trying to solve, the kernel expects a timer > to be up and running when hitting the delay loop calibration. At that > stage, it is impossible to register a platform device, hence the use > (abuse?) of early platform devices. :-) Unfortunately I never did get a chance to read through your entire patch set, so I missed this. > The current ARM code relies on the timers *not* being a standard > device, and being directly setup by an board specific method. The SMP > timers are even worse, as they are directly called by the core code, > meaning that we can only have *one* implementation at a time in the > kernel. > > So the early platform stuff is a potential solution for that, though > there is no way it would handle any kind of dependency. What I dream of > is to have the full device/driver infrastructure available much > earlier, before the rest of the kernel starts relying on some hardware > being up and running... My suggestion: don't use platform_device for this. I think it is entirely the wrong model. Keep the timers *not* standard devices. Instead, use a timer setup function that accepts a list of compatible properties and an initialization hook for each timer type. Since timers have exist, have to be called by core code, and cannot ever be built as modules, the Linux device model really doesn't offer much advantage. It is completely valid and often done to access device tree data from early setup code without any context of a struct device. g.
On 25/06/11 21:44, Grant Likely wrote: > On Sat, Jun 25, 2011 at 12:11:42PM +0100, Marc Zyngier wrote: >> On Fri, 24 Jun 2011 22:49:56 -0600 >> The current ARM code relies on the timers *not* being a standard >> device, and being directly setup by an board specific method. The SMP >> timers are even worse, as they are directly called by the core code, >> meaning that we can only have *one* implementation at a time in the >> kernel. >> >> So the early platform stuff is a potential solution for that, though >> there is no way it would handle any kind of dependency. What I dream of >> is to have the full device/driver infrastructure available much >> earlier, before the rest of the kernel starts relying on some hardware >> being up and running... > > My suggestion: don't use platform_device for this. I think it is > entirely the wrong model. Keep the timers *not* standard devices. > > Instead, use a timer setup function that accepts a list of compatible > properties and an initialization hook for each timer type. Since > timers have exist, have to be called by core code, and cannot ever be > built as modules, the Linux device model really doesn't offer much > advantage. > > It is completely valid and often done to access device tree data from > early setup code without any context of a struct device. Grant, There's a few conflicting aspects we need to reconcile here: - We want to keep the early setup code as simple as possible so it doesn't rely on anything (well, as little as possible) - We want to move driver code out of arch/arm (they often are generic, not specific to a particular architecture) - We want to support DT and non-DT in a similar way (some ARM platforms will never see a DT port) If I follow your advice, I end up with something like the following thing in the core code: extern int timerx_probe(struct of_device_id *id); struct of_device_id timerx_ids[] = { ... }; extern int timery_probe(struct of_device_id *id); struct of_device_id timery_ids[] = { ... }; extern int timerz_probe(struct of_device_id *id); struct of_device_id timerz_ids[] = { ... }; struct arm_timer_probe { struct of_device_if **ids; int (*probe)(struct of_device_id *); }; struct arm_timer_probe arm_timer_probe_list[] = { { .ids = timerx_ids, probe = timerx_probe, }, { .ids = timery_ids, probe = timery_probe, }, { .ids = timerz_ids, probe = timerz_probe, }, { }, }; ... with some additional #ifdef-ery to make that work. This could solve the first two points above, though each timer_probe function has to parse the tree itself to gather resources (code duplication). If you add the non-DT support in the picture, you get an additional, completely separate code path, where the platform code directly calls into the driver code, each platform inventing its own stuff. Again. I think we all agree that early_platform_device are distasteful. They abuse the platform_device and command line. They give you a false sense of infrastructure. But they also offer you: - a clean separation between core code and drivers, with a standardized interface - drivers shared across architectures (sh & shmobile, for example) - use of common code (fetching resources from DT) - a relative independence from the level of DT support (the driver only knows about platform devices). If there are issues in the early platform stuff, I'd rather tackle them instead of just inventing yet another custom mechanism. And if we decide that it is terminally broken, I hope we can agree on something generic enough to satisfy the above requirements. Cheers, M.
diff --git a/drivers/base/core.c b/drivers/base/core.c index bc8729d..83aafff 100644 --- a/drivers/base/core.c +++ b/drivers/base/core.c @@ -588,6 +588,7 @@ void device_initialize(struct device *dev) { dev->kobj.kset = devices_kset; kobject_init(&dev->kobj, &device_ktype); + INIT_LIST_HEAD(&dev->deferred_probe); INIT_LIST_HEAD(&dev->dma_pools); mutex_init(&dev->mutex); lockdep_set_novalidate_class(&dev->mutex); diff --git a/drivers/base/dd.c b/drivers/base/dd.c index 6658da7..3694661 100644 --- a/drivers/base/dd.c +++ b/drivers/base/dd.c @@ -28,6 +28,18 @@ #include "base.h" #include "power/power.h" +/** + * deferred_probe_work_func() - Retry probing devices in the deferred list. + */ +static LIST_HEAD(deferred_probe_list); +static void deferred_probe_work_func(struct work_struct *work) +{ + struct device *dev; + list_for_each_entry(dev, &deferred_probe_list, deferred_probe) { + bus_probe_device(dev); + } +} +static DECLARE_WORK(deferred_probe_work, deferred_probe_work_func); static void driver_bound(struct device *dev) { @@ -41,6 +53,9 @@ static void driver_bound(struct device *dev) __func__, dev->driver->name); klist_add_tail(&dev->p->knode_driver, &dev->driver->p->klist_devices); + if (!list_empty(&dev->deferred_probe)) + list_del_init(&dev->deferred_probe); + schedule_work(&deferred_probe_work); if (dev->bus) blocking_notifier_call_chain(&dev->bus->p->bus_notifier, @@ -142,7 +157,17 @@ probe_failed: driver_sysfs_remove(dev); dev->driver = NULL; - if (ret != -ENODEV && ret != -ENXIO) { + if (ret == -EAGAIN) { + /* + * Probe could not obtain all resources for device and requested + * to be reprobed with the availble drivers at some future point + * in time. Log the deferral request and add the device to the + * deferred probe list. + */ + dev_info(dev, "Driver %s requests probe deferral\n", drv->name); + if (list_empty(&dev->deferred_probe)) + list_add(&dev->deferred_probe, &deferred_probe_list); + } else if (ret != -ENODEV && ret != -ENXIO) { /* driver matched but the probe failed */ printk(KERN_WARNING "%s: probe of %s failed with error %d\n", diff --git a/include/linux/device.h b/include/linux/device.h index c66111a..50cc399 100644 --- a/include/linux/device.h +++ b/include/linux/device.h @@ -506,6 +506,10 @@ struct device_dma_parameters { * @mutex: Mutex to synchronize calls to its driver. * @bus: Type of bus device is on. * @driver: Which driver has allocated this + * @deferred_probe: entry in deferred_probe_list which is used to retry the + * binding of drivers which were unable to get all the resources + * needed by the device; typically because it depends on another + * driver getting probed first. * @platform_data: Platform data specific to the device. * Example: For devices on custom boards, as typical of embedded * and SOC based hardware, Linux often uses platform_data to point @@ -565,6 +569,7 @@ struct device { struct bus_type *bus; /* type of bus device is on */ struct device_driver *driver; /* which driver has allocated this device */ + struct list_head deferred_probe; void *platform_data; /* Platform specific data, device core doesn't touch it */ struct dev_pm_info power;