[PATCH 01/11] drm: Add devm_drm_dev_init/register
Daniel Vetter
daniel at ffwll.ch
Tue Jan 22 19:30:04 UTC 2019
On Tue, Jan 22, 2019 at 8:07 PM Noralf Trønnes <noralf at tronnes.org> wrote:
>
>
>
> Den 22.01.2019 10.32, skrev Daniel Vetter:
> > On Mon, Jan 21, 2019 at 01:21:46PM +0100, Noralf Trønnes wrote:
> >>
> >>
> >> Den 21.01.2019 10.55, skrev Daniel Vetter:
> >>> On Mon, Jan 21, 2019 at 10:10:14AM +0100, Daniel Vetter wrote:
> >>>> On Sun, Jan 20, 2019 at 12:43:08PM +0100, Noralf Trønnes wrote:
> >>>>> This adds resource managed (devres) versions of drm_dev_init() and
> >>>>> drm_dev_register().
> >>>>>
> >>>>> Also added is devm_drm_dev_register_with_fbdev() which sets up generic
> >>>>> fbdev emulation as well.
> >>>>>
> >>>>> devm_drm_dev_register() isn't exported since there are no users.
> >>>>>
> >>>>> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
> >>>>
> >>
> >> <snip>
> >>
> >>>>> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> >>>>> index 381581b01d48..12129772be45 100644
> >>>>> --- a/drivers/gpu/drm/drm_drv.c
> >>>>> +++ b/drivers/gpu/drm/drm_drv.c
> >>>>> @@ -36,6 +36,7 @@
> >>>>>
> >>>>> #include <drm/drm_client.h>
> >>>>> #include <drm/drm_drv.h>
> >>>>> +#include <drm/drm_fb_helper.h>
> >>>>> #include <drm/drmP.h>
> >>>>>
> >>>>> #include "drm_crtc_internal.h"
> >>>>> @@ -871,6 +872,111 @@ void drm_dev_unregister(struct drm_device *dev)
> >>>>> }
> >>>>> EXPORT_SYMBOL(drm_dev_unregister);
> >>>>>
> >>>>> +static void devm_drm_dev_init_release(void *data)
> >>>>> +{
> >>>>> + drm_dev_put(data);
> >>>
> >>> We need drm_dev_unplug() here, or this isn't safe.
> >>
> >> This function is only used to cover the error path if probe fails before
> >> devm_drm_dev_register() is called. devm_drm_dev_register_release() is
> >> the one that calls unplug. There are comments about this in the functions.
> >
> > I think I get a prize for being ignorant and blind :-/
> >
> >>
> >>>
> >>>>> +}
> >>>>> +
> >>>>> +/**
> >>>>> + * devm_drm_dev_init - Resource managed drm_dev_init()
> >>>>> + * @parent: Parent device object
> >>>>> + * @dev: DRM device
> >>>>> + * @driver: DRM driver
> >>>>> + *
> >>>>> + * Managed drm_dev_init(). The DRM device initialized with this function is
> >>>>> + * automatically released on driver detach. You must supply a
> >>>
> >>> I think a bit more clarity here would be good:
> >>>
> >>> "... automatically released on driver unbind by callind drm_dev_unplug()."
> >>>
> >>>>> + * &drm_driver.release callback to control the finalization explicitly.
> >>>
> >>> I think a loud warning for these is in order:
> >>>
> >>> "WARNING:
> >>>
> >>> "In generally it is unsafe to use devm functions for drm structures
> >>> because the lifetimes of &drm_device and the underlying &device do not
> >>> match. This here works because it doesn't immediately free anything, but
> >>> only calls drm_dev_unplug(), which internally decrements the &drm_device
> >>> refcount through drm_dev_put().
> >>>
> >>> "All other drm structures must still be explicitly released in the
> >>> &drm_driver.release callback."
> >>>
> >>> While thinking about this I just realized that with this design we have no
> >>> good place to call drm_atomic_helper_shutdown(). Which we need to, or all
> >>> kinds of things will leak badly (connectors, fb, ...), but there's no
> >>> place to call it:
> >>> - unbind is too early, since we haven't yet called drm_dev_unplug, and the
> >>> drm_dev_unregister in there must be called _before_ we start to shut
> >>> down anything.
> >>> - drm_driver.release is way too late.
> >>>
> >>> Ofc for a real hotunplug there's no point in shutting down the hw (it's
> >>> already gone), but for a driver unload/unbind it would be nice if this
> >>> happens automatically and in the right order.
> >>>
> >>> So not sure what to do here really.
> >>
> >> How about this change: (it breaks the rule of pulling helpers into the
> >> core, so maybe we should put the devm_ functions into the simple KMS
> >> helper instead?)
> >
> > Yeah smells a bit much like midlayer ... What would work is having a pile
> > more devm_ helper functions, so that we onion-unwrap everything correctly,
> > and in the right order. So:
> >
> > - devm_drm_dev_init (always does a drm_dev_put())
> >
> > - devm_drm_poll_enable (shuts down the poll helper with a devm action)
> >
> > - devm_drm_mode_config_reset (does an atomic_helper_shutdown() as it's cleanup action)
> >
> > - devm_drm_dev_register (grabs an additional drm_dev_get() reference so it
> > can call drm_dev_unplug() unconditionally).
> >
>
> Beautiful! I really like this, it's very flexible.
>
> Where should devm_drm_mode_config_reset() live? It will pull in the
> atomic helper...
I think a new drm_devm.c helper would be nice for all this stuff.
Especially since you can't freely mix devm-based setup/cleanup with
normal cleanup I think it'd be good to have it all together in one
place. And perhaps even a code example in the DOC: overview.
> > We'd need to make sure some of the cleanup actions dtrt when the device is
> > gone, but I think we can achieve that by liberally sprinkling
> > drm_dev_enter/exit over them, e.g. the the cleanup action for
> > drm_mode_config_reset would be:
> >
> > {
> > if (drm_dev_enter())
> > return;
> >
> > drm_atomic_helper_shutdown();
> >
> > drm_dev_exit();
> > }
> >
>
> drm_dev_enter() can only be used to check whether the drm_device is
> registered or not, it doesn't say anything about the state of the parent
> device.
>
> All we know is that the device is being unbound from the driver, we
> don't know if it's the device that's being removed or if it's the driver
> that's unregistered.
You're right, both paths will have called drm_dev_unplug by then.
Silly me. I really liked my idea :-)
> I have looked at the various call chains:
>
> driver_unregister ->
> bus_remove_driver ->
> driver_detach ->
> device_release_driver_internal
>
> device_unregister ->
> device_del ->
> bus_remove_device ->
> device_release_driver ->
> device_release_driver_internal
>
> sysfs: unbind_store ->
> device_release_driver ->
> device_release_driver_internal
>
> The only way I've found to differentiate between these in a cleanup
> action is that device_del() uses the bus notifier to signal
> BUS_NOTIFY_DEL_DEVICE before calling bus_remove_device(). Such a
> notifier could be used to set a drm_device->parent_removed flag.
Hm, this might upset Greg KH's code taste ... maybe there's a better
way to do this, but best to prototype a patch with this, send it to
him and ask how to :-)
> Why is it necessary to call drm_atomic_helper_shutdown() here? Doesn't
> everything get disabled when userspace closes? It does in my tinydrm
> world :-)
Iirc fbdev/fbcon can result in leaks ... at least we've had patches
where drivers leaked drm_connector and drm_framebuffer objects, and
they've been fixed by calling drm_atomic_helper_shutdown() in the
unload path. Maybe this is cargo-culting, but it goes way back to
pre-atomic, where drivers called drm_helper_force_disable_all().
If you try to move the fbcon to your tinydrm drivers (con2fb is
apparently the cmdline tool you need, never tried it, I only switch
the kernel's console between fbcon and dummycon and back, not what
fbcon drivers itself), then I think you should be able to reproduce.
And maybe you have a better idea how to deal with this all.
Note also that there's been proposals floating around to only close an
drm_framebuffer, not also remove it (like the current RMFB ioctl
does), with that closing userspace would not necessarily lead to a
full cleanup.
Another thing (which doesn't apply to drm_simple_display_pipe drivers)
is if you have the display on, but no planes showing (i.e. all black).
Then all the fbs will be cleaned up, but drm_connector will be
leaking. That's a case where you need drm_atomic_helper_shutdown()
even if fbcon/fbdev isn't even enabled.
Cheers, Daniel
> > This would be analog to your shutdown parameter below.
> >
> > Essentially I think we can only do the drm_dev_unplug autocleanup in a
> > given driver from devm_drm_dev_register iff all the cleanup actions have
> > been devm-ified, and there's nothing left in it's unbind callback. Because
> > if anything is left in its unbind callback that's a bug, since
> > drm_dev_unregister() (called through drm_dev_unplug) is the very first (or
> > at least one of the very first, before we start cleanup up) functions that
> > need to be called.
> > -Daniel
> >
> >>
> >> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> >> index 12129772be45..7ed9550baff6 100644
> >> --- a/drivers/gpu/drm/drm_drv.c
> >> +++ b/drivers/gpu/drm/drm_drv.c
> >> @@ -34,7 +34,9 @@
> >> #include <linux/slab.h>
> >> #include <linux/srcu.h>
> >>
> >> +#include <drm/drm_atomic_helper.h>
> >> #include <drm/drm_client.h>
> >> +#include <drm/drm_crtc_helper.h>
> >> #include <drm/drm_drv.h>
> >> #include <drm/drm_fb_helper.h>
> >> #include <drm/drmP.h>
> >> @@ -355,17 +357,7 @@ void drm_dev_exit(int idx)
> >> }
> >> EXPORT_SYMBOL(drm_dev_exit);
> >>
> >> -/**
> >> - * drm_dev_unplug - unplug a DRM device
> >> - * @dev: DRM device
> >> - *
> >> - * This unplugs a hotpluggable DRM device, which makes it inaccessible to
> >> - * userspace operations. Entry-points can use drm_dev_enter() and
> >> - * drm_dev_exit() to protect device resources in a race free manner. This
> >> - * essentially unregisters the device like drm_dev_unregister(), but can be
> >> - * called while there are still open users of @dev.
> >> - */
> >> -void drm_dev_unplug(struct drm_device *dev)
> >> +static void __drm_dev_unplug(struct drm_device *dev, bool shutdown)
> >> {
> >> /*
> >> * After synchronizing any critical read section is guaranteed
> >> to see
> >> @@ -378,11 +370,32 @@ void drm_dev_unplug(struct drm_device *dev)
> >>
> >> drm_dev_unregister(dev);
> >>
> >> + if (shutdown)
> >> + drm_kms_helper_poll_fini(dev);
> >> +
> >> mutex_lock(&drm_global_mutex);
> >> - if (dev->open_count == 0)
> >> + if (dev->open_count == 0) {
> >> + if (shutdown)
> >> + drm_atomic_helper_shutdown(dev);
> >> drm_dev_put(dev);
> >> + }
> >> mutex_unlock(&drm_global_mutex);
> >> }
> >> +
> >> +/**
> >> + * drm_dev_unplug - unplug a DRM device
> >> + * @dev: DRM device
> >> + *
> >> + * This unplugs a hotpluggable DRM device, which makes it inaccessible to
> >> + * userspace operations. Entry-points can use drm_dev_enter() and
> >> + * drm_dev_exit() to protect device resources in a race free manner. This
> >> + * essentially unregisters the device like drm_dev_unregister(), but can be
> >> + * called while there are still open users of @dev.
> >> + */
> >> +void drm_dev_unplug(struct drm_device *dev)
> >> +{
> >> + __drm_dev_unplug(dev, false);
> >> +}
> >> EXPORT_SYMBOL(drm_dev_unplug);
> >>
> >> /*
> >> @@ -920,7 +933,7 @@ EXPORT_SYMBOL(devm_drm_dev_init);
> >>
> >> static void devm_drm_dev_register_release(void *data)
> >> {
> >> - drm_dev_unplug(data);
> >> + __drm_dev_unplug(data, true);
> >> }
> >>
> >> static int devm_drm_dev_register(struct drm_device *dev)
> >>
> >>
> >> I realised that we should take a ref on the parent device so it can be
> >> accessed by the DRM_DEV_ functions after unplug.
> >>
> >>
> >> Noralf.
> >>
> >>
> >>>
> >>>>> + *
> >>>>> + * Note: This function must be used together with
> >>>>> + * devm_drm_dev_register_with_fbdev().
> >>>>> + *
> >>>>> + * RETURNS:
> >>>>> + * 0 on success, or error code on failure.
> >>>>> + */
> >>>>> +int devm_drm_dev_init(struct device *parent,
> >>>>> + struct drm_device *dev,
> >>>>> + struct drm_driver *driver)
> >>>>> +{
> >>>>> + int ret;
> >>>>> +
> >>>>> + if (WARN_ON(!parent || !driver->release))
> >>>>> + return -EINVAL;
> >>>>> +
> >>>>> + ret = drm_dev_init(dev, driver, parent);
> >>>>> + if (ret)
> >>>>> + return ret;
> >>>>> +
> >>>>> + /*
> >>>>> + * This is a temporary release action that is used if probing fails
> >>>>> + * before devm_drm_dev_register() is called.
> >>>>> + */
> >>>>> + ret = devm_add_action(parent, devm_drm_dev_init_release, dev);
> >>>>> + if (ret)
> >>>>> + devm_drm_dev_init_release(dev);
> >>>>> +
> >>>>> + return ret;
> >>>>> +}
> >>>>> +EXPORT_SYMBOL(devm_drm_dev_init);
> >>>>> +
> >>>>> +static void devm_drm_dev_register_release(void *data)
> >>>>> +{
> >>>>> + drm_dev_unplug(data);
> >>>>> +}
> >>>>> +
> >>>>> +static int devm_drm_dev_register(struct drm_device *dev)
> >>>>> +{
> >>>>> + int ret;
> >>>>> +
> >>>>> + ret = drm_dev_register(dev, 0);
> >>>>> + if (ret)
> >>>>> + return ret;
> >>>>> +
> >>>>> + /*
> >>>>> + * This has now served it's purpose, remove it to not mess up ref
> >>>>> + * counting.
> >>>>> + */
> >>>>> + devm_remove_action(dev->dev, devm_drm_dev_init_release, dev);
> >>>>> +
> >>>>> + ret = devm_add_action(dev->dev, devm_drm_dev_register_release, dev);
> >>>>> + if (ret)
> >>>>> + devm_drm_dev_register_release(dev);
> >>>>> +
> >>>>> + return ret;
> >>>>> +}
> >>>>> +
> >>>>> +/**
> >>>>> + * devm_drm_dev_register_with_fbdev - Resource managed drm_dev_register()
> >>>>> + * including generic fbdev emulation
> >>>>> + * @dev: DRM device to register
> >>>>> + * @fbdev_bpp: Preferred bits per pixel for fbdev (optional)
> >>>>> + *
> >>>>> + * Managed drm_dev_register() that also calls drm_fbdev_generic_setup().
> >>>>> + * The DRM device registered with this function is automatically unregistered on
> >>>>> + * driver detach using drm_dev_unplug().
> >>>>> + *
> >>>>> + * Note: This function must be used together with devm_drm_dev_init().
> >>>>> + *
> >>>>> + * For testing driver detach can be triggered manually by writing to the driver
> >>>>> + * 'unbind' file.
> >>>>> + *
> >>>>> + * RETURNS:
> >>>>> + * 0 on success, negative error code on failure.
> >>>>> + */
> >>>>> +int devm_drm_dev_register_with_fbdev(struct drm_device *dev,
> >>>>> + unsigned int fbdev_bpp)
> >>>>> +{
> >>>>> + int ret;
> >>>>> +
> >>>>> + ret = devm_drm_dev_register(dev);
> >>>>> + if (ret)
> >>>>> + return ret;
> >>>>> +
> >>>>> + drm_fbdev_generic_setup(dev, fbdev_bpp);
> >>>>> +
> >>>>> + return 0;
> >>>>> +}
> >>>>> +EXPORT_SYMBOL(devm_drm_dev_register_with_fbdev);
> >>>>> +
> >>>>> /**
> >>>>> * drm_dev_set_unique - Set the unique name of a DRM device
> >>>>> * @dev: device of which to set the unique name
> >>>>> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
> >>>>> index 35af23f5fa0d..c3f0477f2e7f 100644
> >>>>> --- a/include/drm/drm_drv.h
> >>>>> +++ b/include/drm/drm_drv.h
> >>>>> @@ -628,6 +628,12 @@ struct drm_device *drm_dev_alloc(struct drm_driver *driver,
> >>>>> int drm_dev_register(struct drm_device *dev, unsigned long flags);
> >>>>> void drm_dev_unregister(struct drm_device *dev);
> >>>>>
> >>>>> +int devm_drm_dev_init(struct device *parent,
> >>>>> + struct drm_device *dev,
> >>>>> + struct drm_driver *driver);
> >>>>> +int devm_drm_dev_register_with_fbdev(struct drm_device *dev,
> >>>>> + unsigned int fbdev_bpp);
> >>>>> +
> >>>>> void drm_dev_get(struct drm_device *dev);
> >>>>> void drm_dev_put(struct drm_device *dev);
> >>>>> void drm_put_dev(struct drm_device *dev);
> >>>>> --
> >>>>> 2.20.1
> >>>>>
> >>>>> _______________________________________________
> >>>>> dri-devel mailing list
> >>>>> dri-devel at lists.freedesktop.org
> >>>>> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> >>>>
> >>>> --
> >>>> Daniel Vetter
> >>>> Software Engineer, Intel Corporation
> >>>> http://blog.ffwll.ch
> >>>
> >
--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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