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author | Kishon Vijay Abraham I <kishon@ti.com> | 2013-09-27 10:23:25 +0400 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2013-09-28 04:35:41 +0400 |
commit | ff764963479a1b18721ab96e531404c50fefe8b1 (patch) | |
tree | e696248868cbb6ab2ac2159058c72631b620b136 /Documentation/phy.txt | |
parent | 6741448eb01a1844b78c83fa8faf0c95524fc09b (diff) | |
download | linux-ff764963479a1b18721ab96e531404c50fefe8b1.tar.xz |
drivers: phy: add generic PHY framework
The PHY framework provides a set of APIs for the PHY drivers to
create/destroy a PHY and APIs for the PHY users to obtain a reference to the
PHY with or without using phandle. For dt-boot, the PHY drivers should
also register *PHY provider* with the framework.
PHY drivers should create the PHY by passing id and ops like init, exit,
power_on and power_off. This framework is also pm runtime enabled.
The documentation for the generic PHY framework is added in
Documentation/phy.txt and the documentation for dt binding can be found at
Documentation/devicetree/bindings/phy/phy-bindings.txt
Cc: Tomasz Figa <t.figa@samsung.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Acked-by: Felipe Balbi <balbi@ti.com>
Tested-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation/phy.txt')
-rw-r--r-- | Documentation/phy.txt | 166 |
1 files changed, 166 insertions, 0 deletions
diff --git a/Documentation/phy.txt b/Documentation/phy.txt new file mode 100644 index 000000000000..0103e4b15b0e --- /dev/null +++ b/Documentation/phy.txt @@ -0,0 +1,166 @@ + PHY SUBSYSTEM + Kishon Vijay Abraham I <kishon@ti.com> + +This document explains the Generic PHY Framework along with the APIs provided, +and how-to-use. + +1. 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). + +2. 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), THIS_MODULE, (xlate)) + +#define devm_of_phy_provider_register(dev, xlate) \ + __devm_of_phy_provider_register((dev), 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. + +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. + +3. 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, const struct phy_ops *ops, + struct phy_init_data *init_data); +struct phy *devm_phy_create(struct device *dev, const struct phy_ops *ops, + struct phy_init_data *init_data); + +The PHY drivers can use one of the above 2 APIs to create the PHY by passing +the device pointer, phy ops and init_data. +phy_ops is a set of function pointers for performing PHY operations such as +init, exit, power_on and power_off. *init_data* is mandatory to get a reference +to the PHY in the case of non-dt boot. See section *Board File Initialization* +on how init_data should be used. + +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 *devm_phy_get(struct device *dev, const char *string); + +phy_get and devm_phy_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 only difference between the two APIs is that devm_phy_get associates the +device with the PHY using devres on successful PHY get. On driver detach, +release function is invoked on the the devres data and devres data is freed. + +5. 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. + +6. 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. + +7. 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. + +8. Board File Initialization + +Certain board file initialization is necessary in order to get a reference +to the PHY in the case of non-dt boot. +Say we have a single device that implements 3 PHYs that of USB, SATA and PCIe, +then in the board file the following initialization should be done. + +struct phy_consumer consumers[] = { + PHY_CONSUMER("dwc3.0", "usb"), + PHY_CONSUMER("pcie.0", "pcie"), + PHY_CONSUMER("sata.0", "sata"), +}; +PHY_CONSUMER takes 2 parameters, first is the device name of the controller +(PHY consumer) and second is the port name. + +struct phy_init_data init_data = { + .consumers = consumers, + .num_consumers = ARRAY_SIZE(consumers), +}; + +static const struct platform_device pipe3_phy_dev = { + .name = "pipe3-phy", + .id = -1, + .dev = { + .platform_data = { + .init_data = &init_data, + }, + }, +}; + +then, while doing phy_create, the PHY driver should pass this init_data + phy_create(dev, ops, pdata->init_data); + +and the controller driver (phy consumer) should pass the port name along with +the device to get a reference to the PHY + phy_get(dev, "pcie"); + +9. DeviceTree Binding + +The documentation for PHY dt binding can be found @ +Documentation/devicetree/bindings/phy/phy-bindings.txt |