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linux-next/Documentation/driver-model/devres.txt
Linus Torvalds 43a0a98aa8 ARM: SoC driver updates for v4.8
Driver updates for ARM SoCs.
 
 A slew of changes this release cycle. The reset driver tree, that we merge
 through arm-soc for historical reasons, is also sizable this time around.
 
 Among the changes:
 
  - clps711x: Treewide changes to compatible strings, merged here for simplicity.
  - Qualcomm: SCM firmware driver cleanups, move to platform driver
  - ux500: Major cleanups, removal of old mach-specific infrastructure.
  - Atmel external bus memory driver
  - Move of brcmstb platform to the rest of bcm
  - PMC driver updates for tegra, various fixes and improvements
  - Samsung platform driver updates to support 64-bit Exynos platforms
  - Reset controller cleanups moving to devm_reset_controller_register() APIs
  - Reset controller driver for Amlogic Meson
  - Reset controller driver for Hisilicon hi6220
  - ARM SCPI power domain support
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Merge tag 'armsoc-drivers' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc

Pull ARM SoC driver updates from Olof Johansson:
 "Driver updates for ARM SoCs.

  A slew of changes this release cycle.  The reset driver tree, that we
  merge through arm-soc for historical reasons, is also sizable this
  time around.

  Among the changes:

   - clps711x: Treewide changes to compatible strings, merged here for simplicity.
   - Qualcomm: SCM firmware driver cleanups, move to platform driver
   - ux500: Major cleanups, removal of old mach-specific infrastructure.
   - Atmel external bus memory driver
   - Move of brcmstb platform to the rest of bcm
   - PMC driver updates for tegra, various fixes and improvements
   - Samsung platform driver updates to support 64-bit Exynos platforms
   - Reset controller cleanups moving to devm_reset_controller_register() APIs
   - Reset controller driver for Amlogic Meson
   - Reset controller driver for Hisilicon hi6220
   - ARM SCPI power domain support"

* tag 'armsoc-drivers' of git://git.kernel.org/pub/scm/linux/kernel/git/arm/arm-soc: (100 commits)
  ARM: ux500: consolidate base platform files
  ARM: ux500: move soc_id driver to drivers/soc
  ARM: ux500: call ux500_setup_id later
  ARM: ux500: consolidate soc_device code in id.c
  ARM: ux500: remove cpu_is_u* helpers
  ARM: ux500: use CLK_OF_DECLARE()
  ARM: ux500: move l2x0 init to .init_irq
  mfd: db8500 stop passing around platform data
  ASoC: ab8500-codec: remove platform data based probe
  ARM: ux500: move ab8500_regulator_plat_data into driver
  ARM: ux500: remove unused regulator data
  soc: raspberrypi-power: add CONFIG_OF dependency
  firmware: scpi: add CONFIG_OF dependency
  video: clps711x-fb: Changing the compatibility string to match with the smallest supported chip
  input: clps711x-keypad: Changing the compatibility string to match with the smallest supported chip
  pwm: clps711x: Changing the compatibility string to match with the smallest supported chip
  serial: clps711x: Changing the compatibility string to match with the smallest supported chip
  irqchip: clps711x: Changing the compatibility string to match with the smallest supported chip
  clocksource: clps711x: Changing the compatibility string to match with the smallest supported chip
  clk: clps711x: Changing the compatibility string to match with the smallest supported chip
  ...
2016-08-01 18:36:01 -04:00

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9.3 KiB
Plaintext

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()
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()
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()
RESET
devm_reset_control_get()
devm_reset_controller_register()
SLAVE DMA ENGINE
devm_acpi_dma_controller_register()
SPI
devm_spi_register_master()
WATCHDOG
devm_watchdog_register_device()