linux/Documentation/driver-model/devres.txt

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Devres - Managed Device Resource
================================
Tejun Heo <teheo@suse.de>
First draft 10 January 2007
1. Intro : Huh? Devres?
2. Devres : Devres in a nutshell
3. Devres Group : Group devres'es and release them together
4. Details : Life time rules, calling context, ...
5. Overhead : How much do we have to pay for this?
6. List of managed interfaces : Currently implemented managed interfaces
1. Intro
--------
devres came up while trying to convert libata to use iomap. Each
iomapped address should be kept and unmapped on driver detach. For
example, a plain SFF ATA controller (that is, good old PCI IDE) in
native mode makes use of 5 PCI BARs and all of them should be
maintained.
As with many other device drivers, libata low level drivers have
sufficient bugs in ->remove and ->probe failure path. Well, yes,
that's probably because libata low level driver developers are lazy
bunch, but aren't all low level driver developers? After spending a
day fiddling with braindamaged hardware with no document or
braindamaged document, if it's finally working, well, it's working.
For one reason or another, low level drivers don't receive as much
attention or testing as core code, and bugs on driver detach or
initialization failure don't happen often enough to be noticeable.
Init failure path is worse because it's much less travelled while
needs to handle multiple entry points.
So, many low level drivers end up leaking resources on driver detach
and having half broken failure path implementation in ->probe() which
would leak resources or even cause oops when failure occurs. iomap
adds more to this mix. So do msi and msix.
2. Devres
---------
devres is basically linked list of arbitrarily sized memory areas
associated with a struct device. Each devres entry is associated with
a release function. A devres can be released in several ways. No
matter what, all devres entries are released on driver detach. On
release, the associated release function is invoked and then the
devres entry is freed.
Managed interface is created for resources commonly used by device
drivers using devres. For example, coherent DMA memory is acquired
using dma_alloc_coherent(). The managed version is called
dmam_alloc_coherent(). It is identical to dma_alloc_coherent() except
for the DMA memory allocated using it is managed and will be
automatically released on driver detach. Implementation looks like
the following.
struct dma_devres {
size_t size;
void *vaddr;
dma_addr_t dma_handle;
};
static void dmam_coherent_release(struct device *dev, void *res)
{
struct dma_devres *this = res;
dma_free_coherent(dev, this->size, this->vaddr, this->dma_handle);
}
dmam_alloc_coherent(dev, size, dma_handle, gfp)
{
struct dma_devres *dr;
void *vaddr;
dr = devres_alloc(dmam_coherent_release, sizeof(*dr), gfp);
...
/* alloc DMA memory as usual */
vaddr = dma_alloc_coherent(...);
...
/* record size, vaddr, dma_handle in dr */
dr->vaddr = vaddr;
...
devres_add(dev, dr);
return vaddr;
}
If a driver uses dmam_alloc_coherent(), the area is guaranteed to be
freed whether initialization fails half-way or the device gets
detached. If most resources are acquired using managed interface, a
driver can have much simpler init and exit code. Init path basically
looks like the following.
my_init_one()
{
struct mydev *d;
d = devm_kzalloc(dev, sizeof(*d), GFP_KERNEL);
if (!d)
return -ENOMEM;
d->ring = dmam_alloc_coherent(...);
if (!d->ring)
return -ENOMEM;
if (check something)
return -EINVAL;
...
return register_to_upper_layer(d);
}
And exit path,
my_remove_one()
{
unregister_from_upper_layer(d);
shutdown_my_hardware();
}
As shown above, low level drivers can be simplified a lot by using
devres. Complexity is shifted from less maintained low level drivers
to better maintained higher layer. Also, as init failure path is
shared with exit path, both can get more testing.
3. Devres group
---------------
Devres entries can be grouped using devres group. When a group is
released, all contained normal devres entries and properly nested
groups are released. One usage is to rollback series of acquired
resources on failure. For example,
if (!devres_open_group(dev, NULL, GFP_KERNEL))
return -ENOMEM;
acquire A;
if (failed)
goto err;
acquire B;
if (failed)
goto err;
...
devres_remove_group(dev, NULL);
return 0;
err:
devres_release_group(dev, NULL);
return err_code;
As resource acquisition failure usually means probe failure, constructs
like above are usually useful in midlayer driver (e.g. libata core
layer) where interface function shouldn't have side effect on failure.
For LLDs, just returning error code suffices in most cases.
Each group is identified by void *id. It can either be explicitly
specified by @id argument to devres_open_group() or automatically
created by passing NULL as @id as in the above example. In both
cases, devres_open_group() returns the group's id. The returned id
can be passed to other devres functions to select the target group.
If NULL is given to those functions, the latest open group is
selected.
For example, you can do something like the following.
int my_midlayer_create_something()
{
if (!devres_open_group(dev, my_midlayer_create_something, GFP_KERNEL))
return -ENOMEM;
...
devres_close_group(dev, my_midlayer_create_something);
return 0;
}
void my_midlayer_destroy_something()
{
devres_release_group(dev, my_midlayer_create_something);
}
4. Details
----------
Lifetime of a devres entry begins on devres allocation and finishes
when it is released or destroyed (removed and freed) - no reference
counting.
devres core guarantees atomicity to all basic devres operations and
has support for single-instance devres types (atomic
lookup-and-add-if-not-found). Other than that, synchronizing
concurrent accesses to allocated devres data is caller's
responsibility. This is usually non-issue because bus ops and
resource allocations already do the job.
For an example of single-instance devres type, read pcim_iomap_table()
in lib/devres.c.
All devres interface functions can be called without context if the
right gfp mask is given.
5. Overhead
-----------
Each devres bookkeeping info is allocated together with requested data
area. With debug option turned off, bookkeeping info occupies 16
bytes on 32bit machines and 24 bytes on 64bit (three pointers rounded
up to ull alignment). If singly linked list is used, it can be
reduced to two pointers (8 bytes on 32bit, 16 bytes on 64bit).
Each devres group occupies 8 pointers. It can be reduced to 6 if
singly linked list is used.
Memory space overhead on ahci controller with two ports is between 300
and 400 bytes on 32bit machine after naive conversion (we can
certainly invest a bit more effort into libata core layer).
6. List of managed interfaces
-----------------------------
CLOCK
devm_clk_get()
devm_clk_put()
devm_clk_hw_register()
DMA
dmam_alloc_coherent()
dmam_alloc_noncoherent()
dmam_declare_coherent_memory()
dmam_free_coherent()
dmam_free_noncoherent()
dmam_pool_create()
dmam_pool_destroy()
GPIO
devm_gpiod_get()
devm_gpiod_get_index()
devm_gpiod_get_index_optional()
devm_gpiod_get_optional()
devm_gpiod_put()
devm_gpiochip_add_data()
devm_gpiochip_remove()
devm_gpio_request()
devm_gpio_request_one()
devm_gpio_free()
IIO
devm_iio_device_alloc()
devm_iio_device_free()
devm_iio_device_register()
devm_iio_device_unregister()
devm_iio_kfifo_allocate()
devm_iio_kfifo_free()
devm_iio_trigger_alloc()
devm_iio_trigger_free()
devm_iio_channel_get()
devm_iio_channel_release()
devm_iio_channel_get_all()
devm_iio_channel_release_all()
INPUT
devm_input_allocate_device()
IO region
devm_release_mem_region()
devm_release_region()
devm_release_resource()
devm_request_mem_region()
devm_request_region()
devm_request_resource()
IOMAP
devm_ioport_map()
devm_ioport_unmap()
devm_ioremap()
devm_ioremap_nocache()
devm_ioremap_wc()
lib: devres: Introduce devm_ioremap_resource() The devm_request_and_ioremap() function is very useful and helps avoid a whole lot of boilerplate. However, one issue that keeps popping up is its lack of a specific error code to determine which of the steps that it performs failed. Furthermore, while the function gives an example and suggests what error code to return on failure, a wide variety of error codes are used throughout the tree. In an attempt to fix these problems, this patch adds a new function that drivers can transition to. The devm_ioremap_resource() returns a pointer to the remapped I/O memory on success or an ERR_PTR() encoded error code on failure. Callers can check for failure using IS_ERR() and determine its cause by extracting the error code using PTR_ERR(). devm_request_and_ioremap() is implemented as a wrapper around the new API and return NULL on failure as before. This ensures that backwards compatibility is maintained until all users have been converted to the new API, at which point the old devm_request_and_ioremap() function should be removed. A semantic patch is included which can be used to convert from the old devm_request_and_ioremap() API to the new devm_ioremap_resource() API. Some non-trivial cases may require manual intervention, though. Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de> Cc: Arnd Bergmann <arnd@arndb.de> Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2013-01-21 10:08:54 +00:00
devm_ioremap_resource() : checks resource, requests memory region, ioremaps
devm_iounmap()
pcim_iomap()
pcim_iomap_regions() : do request_region() and iomap() on multiple BARs
pcim_iomap_table() : array of mapped addresses indexed by BAR
pcim_iounmap()
IRQ
devm_free_irq()
devm_request_any_context_irq()
devm_request_irq()
devm_request_threaded_irq()
LED
devm_led_classdev_register()
devm_led_classdev_unregister()
MDIO
devm_mdiobus_alloc()
devm_mdiobus_alloc_size()
devm_mdiobus_free()
MEM
devm_free_pages()
devm_get_free_pages()
devm_kasprintf()
devm_kcalloc()
devm_kfree()
devm_kmalloc()
devm_kmalloc_array()
devm_kmemdup()
devm_kstrdup()
devm_kvasprintf()
devm_kzalloc()
MFD
devm_mfd_add_devices()
PCI
pcim_enable_device() : after success, all PCI ops become managed
pcim_pin_device() : keep PCI device enabled after release
PHY
devm_usb_get_phy()
devm_usb_put_phy()
Pin control subsystem changes for kernel 3.5: - Generic Device Tree bindings and hooks for drivers so we can move over modern drivers to using this. - Device Tree bindings for Tegra SoCs. - Funneling some devicetree helper code for the drivers/of subsystem. - New pin control drivers for: - Freescale MXS - Freescale i.MX51 - Freescale i.MX53 - All of these use Device Tree bindings. - Dummy pinctrl handles for stepwise migration to pinctrl, akin to dummy regulators. - Minor non-urgent fixes and improvments. -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQIcBAABAgAGBQJPuiZMAAoJEEEQszewGV1zMK4P/RP+RvKs3KnFaAUF/tM2QSll /65BW8SJlaXrbMv5IC4iBvUx1sH/fDNtNjTHIwwlNBlrxPl6TVecvZZq+yBnl7yp Wue0A/xdD0nsD7O/85khVE4WnDJbWpgOdX/9CTVbc6tmTAsb9pGBH2120dtLdcLe X+GRKnf5D05ySHaGKO8j0PB1MLjF/SV3GhGfrYpn0dtW/XVWNmRczLgm0p11qhMd kOLoqjcJUp/p3HYtUjKKnwj/3z0d88YjegsiSelTp9Gdnjp/3c2LrRN91mXdIiMc IGZrp+AQWQ0zg3QrH91gAD7V+f+URrd+IK2EU5PdBO1fqNXgaotGujsX0lqnwycN 8PbXnrUhMhtM4oVjUdLioTP98wIN8Y5tTDoPoVUPtA3921aCVQoE/Pf9/VXBwzEZ O/nmW0hz7e1OraEq4a/vsD715iuxV92lQzJpzMWYjySFyIGur/VCLLWQo95WWK5d Foiif1FTuN+1ueONlI5JHqhFp1HZs0ldVDxR/V8G+ueUNlgQmlypgC3lI++WjXnt uaQS6Hq0NlOKivhlu/uJ098ft7gf2utJLSBOfKPoILgyfksvEGfegJ8tql2YW/vS 42d0jQGrnhi4nctxzGN3zmr4Ys0BU97JP/9Rq+ZbPUL+SDF7e3y4pv+uTLI4ip6v fyHZTFW6CTXbBD3k1qy9 =RgIp -----END PGP SIGNATURE----- Merge tag 'pinctrl-for-v3.5' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl Pull pin control subsystem changes from Linus Walleij: - Generic Device Tree bindings and hooks for drivers so we can move over modern drivers to using this. - Device Tree bindings for Tegra SoCs. - Funneling some devicetree helper code for the drivers/of subsystem. - New pin control drivers for: * Freescale MXS * Freescale i.MX51 * Freescale i.MX53 All of these use Device Tree bindings. - Dummy pinctrl handles for stepwise migration to pinctrl, akin to dummy regulators. - Minor non-urgent fixes and improvments. Fix up trivial conflicts in Documentation/driver-model/devres.txt and drivers/pinctrl/core.c, * tag 'pinctrl-for-v3.5' of git://git.kernel.org/pub/scm/linux/kernel/git/linusw/linux-pinctrl: (46 commits) pinctrl: pinctrl-imx: add imx51 pinctrl driver pinctrl: pinctrl-imx: add imx53 pinctrl driver pinctrl: pinctrl-pxa3xx: remove empty pinmux disable function pinctrl: pinctrl-mxs: remove empty pinmux disable function pinctrl: pinctrl-imx: remove empty pinmux disable function pinctrl: make pinmux disable function optional pinctrl: a minor error checking improvement for pinconf pinctrl: mxs: skip gpio nodes for group creation pinctrl: mxs: create group for pin config node pinctrl: (cosmetic) fix two entries in DocBook comments pinctrl: add more info to error msgs in pin_request pinctrl: add pinctrl-mxs support pinctrl: pinctrl-imx: add imx6q pinctrl driver pinctrl: pinctrl-imx: add imx pinctrl core driver dt: add of_get_child_count helper function pinctrl: support gpio request deferred probing pinctrl: add pinctrl_provide_dummies interface for platforms to use pinctrl: enhance reporting of errors when loading from DT pinctrl: add kerneldoc for pinctrl_ops device tree functions pinctrl: propagate map validation errors ...
2012-05-21 23:58:23 +00:00
PINCTRL
devm_pinctrl_get()
devm_pinctrl_put()
devm_pinctrl_register()
devm_pinctrl_unregister()
PWM
devm_pwm_get()
devm_pwm_put()
REGULATOR
devm_regulator_bulk_get()
devm_regulator_get()
devm_regulator_put()
devm_regulator_register()
SLAVE DMA ENGINE
devm_acpi_dma_controller_register()
SPI
devm_spi_register_master()