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| author | Linus Torvalds <torvalds@linux-foundation.org> | 2026-08-19 10:09:22 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2026-08-19 10:09:22 -0700 |
| commit | f4cdf7ca9a1fdcca413157df19753f388a5a224e (patch) | |
| tree | 60a31895b2446cd7fa27514e8c2843534a0de0da /Documentation/driver-api/driver-model/device.rst | |
| download | linux-stable-f4cdf7ca9a1fdcca413157df19753f388a5a224e.tar.gz linux-stable-f4cdf7ca9a1fdcca413157df19753f388a5a224e.zip | |
Merge tag 'media/v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-mediagrafted
Pull media updates from Mauro Carvalho Chehab:
- v4l2-core: added ISP statistics support and per-block validation
- v4l2-core: Allow unknown HDR10 white point and luminance
- New camera sensors: Sony IMX678 and IMX471m, Himax HM1092 IR sensor
- New codec: Milos: VPU v2.0 codec support
- isp driver: gained support for Dreamchip RPPX1 ISP framework
- vsp1 driver: gained support for RZ/T2H and RZ/N2H
- Novalake driver: gained CVS support for new NVL hardware
- dvb-core: fix feed leak on failed DMX_ADD_PID
- several driver fixes, cleanups and minor improvements
* tag 'media/v7.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (308 commits)
media: ipu-bridge: check all DMI entries when overriding sensor rotation
media: v4l2-async: avoid deleting unlinked ASC entry on link error
media: rzg2l-cru: Align bytesperline to hardware DMA stride requirement
media: intel/ipu6: fix async notifier cleanup leak on parse error
media: staging/ipu7: fix async notifier UAF on probe error path
media: amd: isp4: fix self-deadlock in isp4sd_pwron_and_init() error path
media: amd: isp4: release partial allocations in isp4if_alloc_fw_gpumem()
media: rcar-isp: Fix VSPX reference leaks
media: rcar-isp: Release ISPCORE resources
media: i2c: imx415: Release runtime PM reference on VBLANK error
media: i2c: imx415: Return test pattern write errors
media: renesas: vsp1: Declare index variables in for loop statement
media: renesas: vsp1: Make reset control optional to support platforms without a reset line
media: dt-bindings: media: renesas,vsp1: Document RZ/T2H and RZ/N2H SoCs
media: dt-bindings: media: renesas,fcp: Document RZ/T2H and RZ/N2H SoCs
media: nxp: imx8-isi: Add additional 32-bit RGB format support
media: nxp: imx8-isi: Add 16-bit raw Bayer format support
media: nxp: imx8-isi: Implement per-stream reference counting for multiplexed streams
media: nxp: imx8-isi: Use BIT_ULL() for 64-bit stream masks
media: nxp: imx8-isi: Correct color map between V4L2 and ISI
...
Diffstat (limited to 'Documentation/driver-api/driver-model/device.rst')
| -rw-r--r-- | Documentation/driver-api/driver-model/device.rst | 120 |
1 files changed, 120 insertions, 0 deletions
diff --git a/Documentation/driver-api/driver-model/device.rst b/Documentation/driver-api/driver-model/device.rst new file mode 100644 index 000000000..0833be568 --- /dev/null +++ b/Documentation/driver-api/driver-model/device.rst @@ -0,0 +1,120 @@ +========================== +The Basic Device Structure +========================== + +See the kerneldoc for the struct device. + + +Programming Interface +~~~~~~~~~~~~~~~~~~~~~ +The bus driver that discovers the device uses this to register the +device with the core:: + + int device_register(struct device * dev); + +The bus should initialize the following fields: + + - parent + - name + - bus_id + - bus + +A device is removed from the core when its reference count goes to +0. The reference count can be adjusted using:: + + struct device * get_device(struct device * dev); + void put_device(struct device * dev); + +get_device() will return a pointer to the struct device passed to it +if the reference is not already 0 (if it's in the process of being +removed already). + +A driver can access the lock in the device structure using:: + + void lock_device(struct device * dev); + void unlock_device(struct device * dev); + + +Attributes +~~~~~~~~~~ + +:: + + struct device_attribute { + struct attribute attr; + ssize_t (*show)(struct device *dev, struct device_attribute *attr, + char *buf); + ssize_t (*store)(struct device *dev, struct device_attribute *attr, + const char *buf, size_t count); + }; + +Attributes of devices can be exported by a device driver through sysfs. + +Please see Documentation/filesystems/sysfs.rst for more information +on how sysfs works. + +As explained in Documentation/core-api/kobject.rst, device attributes must be +created before the KOBJ_ADD uevent is generated. The only way to realize +that is by defining an attribute group. + +Attributes are declared using a macro called DEVICE_ATTR:: + + #define DEVICE_ATTR(name,mode,show,store) + +Example::: + + static DEVICE_ATTR(type, 0444, type_show, NULL); + static DEVICE_ATTR(power, 0644, power_show, power_store); + +Helper macros are available for common values of mode, so the above examples +can be simplified to::: + + static DEVICE_ATTR_RO(type); + static DEVICE_ATTR_RW(power); + +This declares two structures of type struct device_attribute with respective +names 'dev_attr_type' and 'dev_attr_power'. These two attributes can be +organized as follows into a group:: + + static struct attribute *dev_attrs[] = { + &dev_attr_type.attr, + &dev_attr_power.attr, + NULL, + }; + + static struct attribute_group dev_group = { + .attrs = dev_attrs, + }; + + static const struct attribute_group *dev_groups[] = { + &dev_group, + NULL, + }; + +A helper macro is available for the common case of a single group, so the +above two structures can be declared using::: + + ATTRIBUTE_GROUPS(dev); + +This array of groups can then be associated with a device by setting the +group pointer in struct device before device_register() is invoked:: + + dev->groups = dev_groups; + device_register(dev); + +The device_register() function will use the 'groups' pointer to create the +device attributes and the device_unregister() function will use this pointer +to remove the device attributes. + +Word of warning: While the kernel allows device_create_file() and +device_remove_file() to be called on a device at any time, userspace has +strict expectations on when attributes get created. When a new device is +registered in the kernel, a uevent is generated to notify userspace (like +udev) that a new device is available. If attributes are added after the +device is registered, then userspace won't get notified and userspace will +not know about the new attributes. + +This is important for device driver that need to publish additional +attributes for a device at driver probe time. If the device driver simply +calls device_create_file() on the device structure passed to it, then +userspace will never be notified of the new attributes. |
