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author | Mauro Carvalho Chehab <mchehab+samsung@kernel.org> | 2019-06-27 16:36:04 -0300 |
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committer | Mauro Carvalho Chehab <mchehab+samsung@kernel.org> | 2019-07-15 11:03:03 -0300 |
commit | 4745dc8abb0a0a9851c07265eea01d844886d5c8 (patch) | |
tree | 06ef361f1770e804f9bce85fb440328a6125187d /Documentation/driver-api/phy/phy.rst | |
parent | 65388dad1bbb51a4eb6cc91b9fa865b57646fb67 (diff) | |
download | linux-stable-4745dc8abb0a0a9851c07265eea01d844886d5c8.tar.gz linux-stable-4745dc8abb0a0a9851c07265eea01d844886d5c8.tar.bz2 linux-stable-4745dc8abb0a0a9851c07265eea01d844886d5c8.zip |
docs: phy: place documentation under driver-api
This subsystem-specific documentation belongs to the
driver-api.
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Diffstat (limited to 'Documentation/driver-api/phy/phy.rst')
-rw-r--r-- | Documentation/driver-api/phy/phy.rst | 197 |
1 files changed, 197 insertions, 0 deletions
diff --git a/Documentation/driver-api/phy/phy.rst b/Documentation/driver-api/phy/phy.rst new file mode 100644 index 000000000000..457c3e0f86d6 --- /dev/null +++ b/Documentation/driver-api/phy/phy.rst @@ -0,0 +1,197 @@ +============= +PHY subsystem +============= + +:Author: Kishon Vijay Abraham I <kishon@ti.com> + +This document explains the Generic PHY Framework along with the APIs provided, +and how-to-use. + +Introduction +============ + +*PHY* is the abbreviation for physical layer. It is used to connect a device +to the physical medium e.g., the USB controller has a PHY to provide functions +such as serialization, de-serialization, encoding, decoding and is responsible +for obtaining the required data transmission rate. Note that some USB +controllers have PHY functionality embedded into it and others use an external +PHY. Other peripherals that use PHY include Wireless LAN, Ethernet, +SATA etc. + +The intention of creating this framework is to bring the PHY drivers spread +all over the Linux kernel to drivers/phy to increase code re-use and for +better code maintainability. + +This framework will be of use only to devices that use external PHY (PHY +functionality is not embedded within the controller). + +Registering/Unregistering the PHY provider +========================================== + +PHY provider refers to an entity that implements one or more PHY instances. +For the simple case where the PHY provider implements only a single instance of +the PHY, the framework provides its own implementation of of_xlate in +of_phy_simple_xlate. If the PHY provider implements multiple instances, it +should provide its own implementation of of_xlate. of_xlate is used only for +dt boot case. + +:: + + #define of_phy_provider_register(dev, xlate) \ + __of_phy_provider_register((dev), NULL, THIS_MODULE, (xlate)) + + #define devm_of_phy_provider_register(dev, xlate) \ + __devm_of_phy_provider_register((dev), NULL, THIS_MODULE, + (xlate)) + +of_phy_provider_register and devm_of_phy_provider_register macros can be used to +register the phy_provider and it takes device and of_xlate as +arguments. For the dt boot case, all PHY providers should use one of the above +2 macros to register the PHY provider. + +Often the device tree nodes associated with a PHY provider will contain a set +of children that each represent a single PHY. Some bindings may nest the child +nodes within extra levels for context and extensibility, in which case the low +level of_phy_provider_register_full() and devm_of_phy_provider_register_full() +macros can be used to override the node containing the children. + +:: + + #define of_phy_provider_register_full(dev, children, xlate) \ + __of_phy_provider_register(dev, children, THIS_MODULE, xlate) + + #define devm_of_phy_provider_register_full(dev, children, xlate) \ + __devm_of_phy_provider_register_full(dev, children, + THIS_MODULE, xlate) + + void devm_of_phy_provider_unregister(struct device *dev, + struct phy_provider *phy_provider); + void of_phy_provider_unregister(struct phy_provider *phy_provider); + +devm_of_phy_provider_unregister and of_phy_provider_unregister can be used to +unregister the PHY. + +Creating the PHY +================ + +The PHY driver should create the PHY in order for other peripheral controllers +to make use of it. The PHY framework provides 2 APIs to create the PHY. + +:: + + struct phy *phy_create(struct device *dev, struct device_node *node, + const struct phy_ops *ops); + struct phy *devm_phy_create(struct device *dev, + struct device_node *node, + const struct phy_ops *ops); + +The PHY drivers can use one of the above 2 APIs to create the PHY by passing +the device pointer and phy ops. +phy_ops is a set of function pointers for performing PHY operations such as +init, exit, power_on and power_off. + +Inorder to dereference the private data (in phy_ops), the phy provider driver +can use phy_set_drvdata() after creating the PHY and use phy_get_drvdata() in +phy_ops to get back the private data. + +4. Getting a reference to the PHY + +Before the controller can make use of the PHY, it has to get a reference to +it. This framework provides the following APIs to get a reference to the PHY. + +:: + + struct phy *phy_get(struct device *dev, const char *string); + struct phy *phy_optional_get(struct device *dev, const char *string); + struct phy *devm_phy_get(struct device *dev, const char *string); + struct phy *devm_phy_optional_get(struct device *dev, + const char *string); + struct phy *devm_of_phy_get_by_index(struct device *dev, + struct device_node *np, + int index); + +phy_get, phy_optional_get, devm_phy_get and devm_phy_optional_get can +be used to get the PHY. In the case of dt boot, the string arguments +should contain the phy name as given in the dt data and in the case of +non-dt boot, it should contain the label of the PHY. The two +devm_phy_get associates the device with the PHY using devres on +successful PHY get. On driver detach, release function is invoked on +the devres data and devres data is freed. phy_optional_get and +devm_phy_optional_get should be used when the phy is optional. These +two functions will never return -ENODEV, but instead returns NULL when +the phy cannot be found.Some generic drivers, such as ehci, may use multiple +phys and for such drivers referencing phy(s) by name(s) does not make sense. In +this case, devm_of_phy_get_by_index can be used to get a phy reference based on +the index. + +It should be noted that NULL is a valid phy reference. All phy +consumer calls on the NULL phy become NOPs. That is the release calls, +the phy_init() and phy_exit() calls, and phy_power_on() and +phy_power_off() calls are all NOP when applied to a NULL phy. The NULL +phy is useful in devices for handling optional phy devices. + +Releasing a reference to the PHY +================================ + +When the controller no longer needs the PHY, it has to release the reference +to the PHY it has obtained using the APIs mentioned in the above section. The +PHY framework provides 2 APIs to release a reference to the PHY. + +:: + + void phy_put(struct phy *phy); + void devm_phy_put(struct device *dev, struct phy *phy); + +Both these APIs are used to release a reference to the PHY and devm_phy_put +destroys the devres associated with this PHY. + +Destroying the PHY +================== + +When the driver that created the PHY is unloaded, it should destroy the PHY it +created using one of the following 2 APIs:: + + void phy_destroy(struct phy *phy); + void devm_phy_destroy(struct device *dev, struct phy *phy); + +Both these APIs destroy the PHY and devm_phy_destroy destroys the devres +associated with this PHY. + +PM Runtime +========== + +This subsystem is pm runtime enabled. So while creating the PHY, +pm_runtime_enable of the phy device created by this subsystem is called and +while destroying the PHY, pm_runtime_disable is called. Note that the phy +device created by this subsystem will be a child of the device that calls +phy_create (PHY provider device). + +So pm_runtime_get_sync of the phy_device created by this subsystem will invoke +pm_runtime_get_sync of PHY provider device because of parent-child relationship. +It should also be noted that phy_power_on and phy_power_off performs +phy_pm_runtime_get_sync and phy_pm_runtime_put respectively. +There are exported APIs like phy_pm_runtime_get, phy_pm_runtime_get_sync, +phy_pm_runtime_put, phy_pm_runtime_put_sync, phy_pm_runtime_allow and +phy_pm_runtime_forbid for performing PM operations. + +PHY Mappings +============ + +In order to get reference to a PHY without help from DeviceTree, the framework +offers lookups which can be compared to clkdev that allow clk structures to be +bound to devices. A lookup can be made be made during runtime when a handle to +the struct phy already exists. + +The framework offers the following API for registering and unregistering the +lookups:: + + int phy_create_lookup(struct phy *phy, const char *con_id, + const char *dev_id); + void phy_remove_lookup(struct phy *phy, const char *con_id, + const char *dev_id); + +DeviceTree Binding +================== + +The documentation for PHY dt binding can be found @ +Documentation/devicetree/bindings/phy/phy-bindings.txt |