3 ====================================
4 Samsung USB 2.0 PHY adaptation layer
5 ====================================
10 The architecture of the USB 2.0 PHY module in Samsung SoCs is similar
11 among many SoCs. In spite of the similarities it proved difficult to
12 create a one driver that would fit all these PHY controllers. Often
13 the differences were minor and were found in particular bits of the
14 registers of the PHY. In some rare cases the order of register writes or
15 the PHY powering up process had to be altered. This adaptation layer is
16 a compromise between having separate drivers and having a single driver
17 with added support for many special cases.
23 This is the main file of the adaptation layer. This file contains
24 the probe function and provides two callbacks to the Generic PHY
25 Framework. This two callbacks are used to power on and power off the
26 phy. They carry out the common work that has to be done on all version
27 of the PHY module. Depending on which SoC was chosen they execute SoC
28 specific callbacks. The specific SoC version is selected by choosing
29 the appropriate compatible string. In addition, this file contains
30 struct of_device_id definitions for particular SoCs.
33 This is the include file. It declares the structures used by this
34 driver. In addition it should contain extern declarations for
35 structures that describe particular SoCs.
40 To support a new SoC a new file should be added to the drivers/phy
41 directory. Each SoC's configuration is stored in an instance of the
42 struct samsung_usb2_phy_config::
44 struct samsung_usb2_phy_config {
45 const struct samsung_usb2_common_phy *phys;
46 int (*rate_to_clk)(unsigned long, u32 *);
47 unsigned int num_phys;
51 The num_phys is the number of phys handled by the driver. `*phys` is an
52 array that contains the configuration for each phy. The has_mode_switch
53 property is a boolean flag that determines whether the SoC has USB host
54 and device on a single pair of pins. If so, a special register has to
55 be modified to change the internal routing of these pins between a USB
56 device or host module.
58 For example the configuration for Exynos 4210 is following::
60 const struct samsung_usb2_phy_config exynos4210_usb2_phy_config = {
62 .num_phys = EXYNOS4210_NUM_PHYS,
63 .phys = exynos4210_phys,
64 .rate_to_clk = exynos4210_rate_to_clk,
67 - `int (*rate_to_clk)(unsigned long, u32 *)`
69 The rate_to_clk callback is to convert the rate of the clock
70 used as the reference clock for the PHY module to the value
71 that should be written in the hardware register.
73 The exynos4210_phys configuration array is as follows::
75 static const struct samsung_usb2_common_phy exynos4210_phys[] = {
78 .id = EXYNOS4210_DEVICE,
79 .power_on = exynos4210_power_on,
80 .power_off = exynos4210_power_off,
84 .id = EXYNOS4210_HOST,
85 .power_on = exynos4210_power_on,
86 .power_off = exynos4210_power_off,
90 .id = EXYNOS4210_HSIC0,
91 .power_on = exynos4210_power_on,
92 .power_off = exynos4210_power_off,
96 .id = EXYNOS4210_HSIC1,
97 .power_on = exynos4210_power_on,
98 .power_off = exynos4210_power_off,
103 - `int (*power_on)(struct samsung_usb2_phy_instance *);`
104 `int (*power_off)(struct samsung_usb2_phy_instance *);`
106 These two callbacks are used to power on and power off the phy
107 by modifying appropriate registers.
109 Final change to the driver is adding appropriate compatible value to the
110 phy-samsung-usb2.c file. In case of Exynos 4210 the following lines were
111 added to the struct of_device_id samsung_usb2_phy_of_match[] array::
113 #ifdef CONFIG_PHY_EXYNOS4210_USB2
115 .compatible = "samsung,exynos4210-usb2-phy",
116 .data = &exynos4210_usb2_phy_config,
120 To add further flexibility to the driver the Kconfig file enables to
121 include support for selected SoCs in the compiled driver. The Kconfig
122 entry for Exynos 4210 is following::
124 config PHY_EXYNOS4210_USB2
125 bool "Support for Exynos 4210"
126 depends on PHY_SAMSUNG_USB2
127 depends on CPU_EXYNOS4210
129 Enable USB PHY support for Exynos 4210. This option requires that
130 Samsung USB 2.0 PHY driver is enabled and means that support for this
131 particular SoC is compiled in the driver. In case of Exynos 4210 four
132 phys are available - device, host, HSCI0 and HSCI1.
134 The newly created file that supports the new SoC has to be also added to the
135 Makefile. In case of Exynos 4210 the added line is following::
137 obj-$(CONFIG_PHY_EXYNOS4210_USB2) += phy-exynos4210-usb2.o
139 After completing these steps the support for the new SoC should be ready.