[PATCH] drm/doc: Update docs about device instance setup
Laurent Pinchart
laurent.pinchart at ideasonboard.com
Tue Sep 29 06:28:15 PDT 2015
Hi Daniel,
Thank you for the patch.
On Monday 28 September 2015 21:46:35 Daniel Vetter wrote:
> ->load is deprecated, bus functions are deprecated and everyone
> should use drm_dev_alloc®ister.
>
> So update the .tmpl (and pull a bunch of the overview docs into the
> sourcecode to increase chances that it'll stay in sync in the future)
> and add notes to functions which are deprecated. I didn't bother to
> clean up and document the unload sequence similarly since that one is
> still a bit a mess: drm_dev_unregister does way too much,
> drm_unplug_dev does what _unregister should be doing but then has the
> complication of promising something it doesn't actually do (it doesn't
> unplug existing open fds for instance, only prevents new ones).
>
> Motivated since I don't want to hunt every new driver for usage of
> drm_platform_init any more ;-)
>
> v2: Reword the deprecation note for ->load a bit, using Laurent's
> suggestion as an example (but making the wording a bit stronger even).
> Fix spelling in commit message.
>
> Cc: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
> Cc: David Herrmann <dh.herrmann at gmail.com>
> Acked-by: David Herrmann <dh.herrmann at gmail.com>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> ---
> Documentation/DocBook/drm.tmpl | 99 +++++++--------------------------------
> drivers/gpu/drm/drm_drv.c | 55 +++++++++++++++++++++--
> drivers/gpu/drm/drm_pci.c | 11 +++++
> drivers/gpu/drm/drm_platform.c | 3 ++
> 4 files changed, 83 insertions(+), 85 deletions(-)
>
> diff --git a/Documentation/DocBook/drm.tmpl b/Documentation/DocBook/drm.tmpl
> index 5395cde6905e..6d24ebb97cda 100644
> --- a/Documentation/DocBook/drm.tmpl
> +++ b/Documentation/DocBook/drm.tmpl
> @@ -138,14 +138,10 @@
> <para>
> At the core of every DRM driver is a
> <structname>drm_driver</structname> structure. Drivers typically statically
> initialize a drm_driver structure, - and then pass it to one of the
> <function>drm_*_init()</function> functions - to register it with the
> DRM subsystem.
> - </para>
> - <para>
> - Newer drivers that no longer require a
> <structname>drm_bus</structname> - structure can alternatively use the
> low-level device initialization and - registration functions such as
> <function>drm_dev_alloc()</function> and -
> <function>drm_dev_register()</function> directly.
> + and then pass it to <function>drm_dev_alloc()</function> to allocate
> a + device instance. After the device instance is fully initialized it
> can be + registered (which makes it accessible from userspace) using +
> <function>drm_dev_register()</function>.
> </para>
> <para>
> The <structname>drm_driver</structname> structure contains static
> @@ -296,83 +292,12 @@ char *date;</synopsis>
> </sect3>
> </sect2>
> <sect2>
> - <title>Device Registration</title>
> - <para>
> - A number of functions are provided to help with device
> registration. - The functions deal with PCI and platform devices,
> respectively. - </para>
> -!Edrivers/gpu/drm/drm_pci.c
> -!Edrivers/gpu/drm/drm_platform.c
> - <para>
> - New drivers that no longer rely on the services provided by the
> - <structname>drm_bus</structname> structure can call the low-level
> - device registration functions directly. The
> - <function>drm_dev_alloc()</function> function can be used to
> allocate - and initialize a new <structname>drm_device</structname>
> structure. - Drivers will typically want to perform some additional
> setup on this - structure, such as allocating driver-specific data
> and storing a - pointer to it in the DRM device's
> <structfield>dev_private</structfield> - field. Drivers should also
> set the device's unique name using the -
> <function>drm_dev_set_unique()</function> function. After it has been -
> set up a device can be registered with the DRM subsystem by calling -
> <function>drm_dev_register()</function>. This will cause the device to
> - be exposed to userspace and will call the driver's
> - <structfield>.load()</structfield> implementation. When a device is
> - removed, the DRM device can safely be unregistered and freed by
> calling - <function>drm_dev_unregister()</function> followed by a
> call to - <function>drm_dev_unref()</function>.
> - </para>
> + <title>Device Instance and Driver Handling</title>
> +!Pdrivers/gpu/drm/drm_drv.c driver instance overview
> !Edrivers/gpu/drm/drm_drv.c
> </sect2>
> <sect2>
> <title>Driver Load</title>
> - <para>
> - The <methodname>load</methodname> method is the driver and device
> - initialization entry point. The method is responsible for
> allocating and - initializing driver private data, performing resource
> allocation and - mapping (e.g. acquiring
> - clocks, mapping registers or allocating command buffers),
> initializing - the memory manager (<xref
> linkend="drm-memory-management"/>), installing - the IRQ handler
> (<xref linkend="drm-irq-registration"/>), setting up - vertical
> blanking handling (<xref linkend="drm-vertical-blank"/>), mode - setting
> (<xref linkend="drm-mode-setting"/>) and initial output
> - configuration (<xref linkend="drm-kms-init"/>).
> - </para>
> - <note><para>
> - If compatibility is a concern (e.g. with drivers converted over
> from - User Mode Setting to Kernel Mode Setting), care must be taken
> to prevent - device initialization and control that is incompatible
> with currently - active userspace drivers. For instance, if user
> level mode setting - drivers are in use, it would be problematic to
> perform output discovery - & configuration at load time.
> Likewise, if user-level drivers - unaware of memory management are
> in use, memory management and command - buffer setup may need to be
> omitted. These requirements are - driver-specific, and care needs to
> be taken to keep both old and new - applications and libraries
> working.
> - </para></note>
> - <synopsis>int (*load) (struct drm_device *, unsigned long
> flags);</synopsis> - <para>
> - The method takes two arguments, a pointer to the newly created
> - <structname>drm_device</structname> and flags. The flags are used to
> - pass the <structfield>driver_data</structfield> field of the device id
> - corresponding to the device passed to <function>drm_*_init()</function>.
> - Only PCI devices currently use this, USB and platform DRM drivers have
> - their <methodname>load</methodname> method called with flags to 0.
> - </para>
> - <sect3>
> - <title>Driver Private Data</title>
> - <para>
> - The driver private hangs off the main
> - <structname>drm_device</structname> structure and can be used for
> - tracking various device-specific bits of information, like
> register
> - offsets, command buffer status, register state for
> suspend/resume, etc.
> - At load time, a driver may simply allocate one and set
> -
> <structname>drm_device</structname>.<structfield>dev_priv</structfield> -
> appropriately; it should be freed and
> -
> <structname>drm_device</structname>.<structfield>dev_priv</structfield> -
> set to NULL when the driver is unloaded.
> - </para>
> - </sect3>
Shouldn't we keep the "Driver Private Data" section ?
> <sect3 id="drm-irq-registration">
> <title>IRQ Registration</title>
> <para>
> @@ -465,6 +390,18 @@ char *date;</synopsis>
> </para>
> </sect3>
> </sect2>
> + <sect2>
> + <title>Bus-specific Device Registration and PCI Support</title>
> + <para>
> + A number of functions are provided to help with device
> registration. + The functions deal with PCI and platform devices
> respectively and are + only provided for historical reasons. These are all
> deprecated and + shouldn't be used in new drivers. Besides that there's a
> few
> + helpers for pci drivers.
> + </para>
> +!Edrivers/gpu/drm/drm_pci.c
> +!Edrivers/gpu/drm/drm_platform.c
> + </sect2>
> </sect1>
>
> <!-- Internals: memory management -->
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index 9ad823fcde87..031c69b71547 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -397,15 +397,51 @@ void drm_minor_release(struct drm_minor *minor)
> }
>
> /**
> + * DOC: driver instance overview
> + *
> + * A device instance for a drm driver is represented by struct &drm_device.
> This
> + * is allocated with drm_dev_alloc(), usually from bus-specific ->probe()
> + * callbacks implemented by the driver. The driver then needs to initialize
> all
> + * the various subsystems for the drm device like memory management, vblank
> + * handling, modesetting support and intial output configuration plus
> obviously
> + * initialize all the corresponding hardware bits. An important part of
> this is
> + * also calling drm_dev_set_unique() to set the userspace-visible unique
> name of
> + * this device instance. Finally when everything is up and running and
> ready for
> + * userspace the device instance can be published using drm_dev_register().
> + *
> + * There is also deprecated support for initalizing device instances using
> + * bus-specific helpers and the ->load() callback. But due to
> + * backwards-compatibility needs the device instance has to be published
> too
> + * early, which requires unpretty global locking to make safe and is
> therefore
> + * only support for existing drivers not yet converted to the new scheme.
> + *
> + * When cleaning up a device instance everything needs to be done in
> revers:
s/revers/reverse/
> + * First unpublish the device instance with drm_dev_unregister(). Then
> clean up
> + * any other resources allocated at device initialization and drop the
> driver's
> + * reference to &drm_device using drm_dev_unref().
> + *
> + * Note that the lifetime rules for &drm_device instance has still a lot of
s/has/have/
> + * historical baggage. Hence use the reference counting provided by
> + * drm_dev_ref() and drm_dev_unref() only carefully.
> + *
> + * Also note that embedding of &drm_device is currently not (yet) supported
> (but
> + * it would be easy to add). Drivers can store driver-private data in the
> + * dev_priv field of &drm_device.
> + */
> +
> +/**
> * drm_put_dev - Unregister and release a DRM device
> * @dev: DRM device
> *
> * Called at module unload time or when a PCI device is unplugged.
> *
> - * Use of this function is discouraged. It will eventually go away
> completely.
> - * Please use drm_dev_unregister() and drm_dev_unref() explicitly instead.
> - *
> * Cleans up all DRM device, calling drm_lastclose().
> + *
> + * Note: Use of this function is deprecated. It will eventually go away
> + * completely. Please use drm_dev_unregister() and drm_dev_unref()
> explicitly
> + * instead to make sure that the device isn't userspace accessible any more
> + * while teardown is in progress, to make sure userspace can't access an
I'd s/to make sure/ensuring that/ in order to avoid the double "to make sure"
in the same sentence.
> + * inconsisten state.
s/inconsisten/inconsistent/
> */
> void drm_put_dev(struct drm_device *dev)
> {
> @@ -518,7 +554,9 @@ static void drm_fs_inode_free(struct inode *inode)
> *
> * Allocate and initialize a new DRM device. No device registration is
> done. * Call drm_dev_register() to advertice the device to user space and
> register it - * with other core subsystems.
> + * with other core subsystems. This should be done last in the device
> + * initialization sequence to make sure userspace can't access an
> inconsistent + * state.
> *
> * The initial ref-count of the object is 1. Use drm_dev_ref() and
> * drm_dev_unref() to take and drop further ref-counts.
> @@ -673,6 +711,12 @@ EXPORT_SYMBOL(drm_dev_unref);
> *
> * Never call this twice on any device!
> *
> + * NOTE: To ensure backward compatibility with existing drivers method this
> + * function calls the ->load() method after registering the device nodes,
> + * creating race conditions. Usage of the ->load() methods is therefore +
> * deprecated, drivers must perform all initialization before calling + *
> drm_dev_register().
> + *
> * RETURNS:
> * 0 on success, negative error code on failure.
> */
> @@ -720,6 +764,9 @@ EXPORT_SYMBOL(drm_dev_register);
> * Unregister the DRM device from the system. This does the reverse of
> * drm_dev_register() but does not deallocate the device. The caller must
> call * drm_dev_unref() to drop their final reference.
> + *
> + * This should be called first in the device teardown code to make sure
> + * userspace can't access the device instance any more.
> */
> void drm_dev_unregister(struct drm_device *dev)
> {
> diff --git a/drivers/gpu/drm/drm_pci.c b/drivers/gpu/drm/drm_pci.c
> index 1b1bd42b0368..fcd2a86acd2c 100644
> --- a/drivers/gpu/drm/drm_pci.c
> +++ b/drivers/gpu/drm/drm_pci.c
> @@ -266,6 +266,9 @@ void drm_pci_agp_destroy(struct drm_device *dev)
> * then register the character device and inter module information.
> * Try and register, if we fail to register, backout previous work.
> *
> + * NOTE: This function is deprecated, please use drm_dev_alloc() and
> + * drm_dev_register() instead and remove your ->load() callback.
> + *
> * Return: 0 on success or a negative error code on failure.
> */
> int drm_get_pci_dev(struct pci_dev *pdev, const struct pci_device_id *ent,
> @@ -326,6 +329,10 @@ EXPORT_SYMBOL(drm_get_pci_dev);
> * Initializes a drm_device structures, registering the stubs and
> initializing * the AGP device.
> *
> + * NOTE: This function is deprecated. Modern modesetting drm drivers should
> use + * pci_register_driver() directly, this function only provides
> shadow-binding + * support for old legacy drivers on top of that core pci
> function. + *
> * Return: 0 on success or a negative error code on failure.
> */
> int drm_pci_init(struct drm_driver *driver, struct pci_driver *pdriver)
> @@ -435,6 +442,10 @@ EXPORT_SYMBOL(drm_pci_init);
> *
> * Unregisters one or more devices matched by a PCI driver from the DRM
> * subsystem.
> + *
> + * NOTE: This function is deprecated. Modern modesetting drm drivers should
> use + * pci_unregister_driver() directly, this function only provides
> shadow-binding + * support for old legacy drivers on top of that core pci
> function. */
> void drm_pci_exit(struct drm_driver *driver, struct pci_driver *pdriver)
> {
> diff --git a/drivers/gpu/drm/drm_platform.c b/drivers/gpu/drm/drm_platform.c
> index 5314c9d5fef4..644169e1a029 100644
> --- a/drivers/gpu/drm/drm_platform.c
> +++ b/drivers/gpu/drm/drm_platform.c
> @@ -95,6 +95,9 @@ EXPORT_SYMBOL(drm_platform_set_busid);
> * subsystem, initializing a drm_device structure and calling the driver's
> * .load() function.
> *
> + * NOTE: This function is deprecated, please use drm_dev_alloc() and
> + * drm_dev_register() instead and remove your ->load() callback.
> + *
> * Return: 0 on success or a negative error code on failure.
> */
> int drm_platform_init(struct drm_driver *driver, struct platform_device
> *platform_device)
--
Regards,
Laurent Pinchart
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