--- /dev/null
+.------------------------------------------------------------------------------+
+| Samsung USB 2.0 PHY adaptation layer |
++-----------------------------------------------------------------------------+'
+
+| 1. Description
++----------------
+
+The architecture of the USB 2.0 PHY module in Samsung SoCs is similar
+among many SoCs. In spite of the similarities it proved difficult to
+create a one driver that would fit all these PHY controllers. Often
+the differences were minor and were found in particular bits of the
+registers of the PHY. In some rare cases the order of register writes or
+the PHY powering up process had to be altered. This adaptation layer is
+a compromise between having separate drivers and having a single driver
+with added support for many special cases.
+
+| 2. Files description
++----------------------
+
+- phy-samsung-usb2.c
+ This is the main file of the adaptation layer. This file contains
+ the probe function and provides two callbacks to the Generic PHY
+ Framework. This two callbacks are used to power on and power off the
+ phy. They carry out the common work that has to be done on all version
+ of the PHY module. Depending on which SoC was chosen they execute SoC
+ specific callbacks. The specific SoC version is selected by choosing
+ the appropriate compatible string. In addition, this file contains
+ struct of_device_id definitions for particular SoCs.
+
+- phy-samsung-usb2.h
+ This is the include file. It declares the structures used by this
+ driver. In addition it should contain extern declarations for
+ structures that describe particular SoCs.
+
+| 3. Supporting SoCs
++--------------------
+
+To support a new SoC a new file should be added to the drivers/phy
+directory. Each SoC's configuration is stored in an instance of the
+struct samsung_usb2_phy_config.
+
+struct samsung_usb2_phy_config {
+ const struct samsung_usb2_common_phy *phys;
+ int (*rate_to_clk)(unsigned long, u32 *);
+ unsigned int num_phys;
+ bool has_mode_switch;
+};
+
+The num_phys is the number of phys handled by the driver. *phys is an
+array that contains the configuration for each phy. The has_mode_switch
+property is a boolean flag that determines whether the SoC has USB host
+and device on a single pair of pins. If so, a special register has to
+be modified to change the internal routing of these pins between a USB
+device or host module.
+
+For example the configuration for Exynos 4210 is following:
+
+const struct samsung_usb2_phy_config exynos4210_usb2_phy_config = {
+ .has_mode_switch = 0,
+ .num_phys = EXYNOS4210_NUM_PHYS,
+ .phys = exynos4210_phys,
+ .rate_to_clk = exynos4210_rate_to_clk,
+}
+
+- int (*rate_to_clk)(unsigned long, u32 *)
+ The rate_to_clk callback is to convert the rate of the clock
+ used as the reference clock for the PHY module to the value
+ that should be written in the hardware register.
+
+The exynos4210_phys configuration array is as follows:
+
+static const struct samsung_usb2_common_phy exynos4210_phys[] = {
+ {
+ .label = "device",
+ .id = EXYNOS4210_DEVICE,
+ .power_on = exynos4210_power_on,
+ .power_off = exynos4210_power_off,
+ },
+ {
+ .label = "host",
+ .id = EXYNOS4210_HOST,
+ .power_on = exynos4210_power_on,
+ .power_off = exynos4210_power_off,
+ },
+ {
+ .label = "hsic0",
+ .id = EXYNOS4210_HSIC0,
+ .power_on = exynos4210_power_on,
+ .power_off = exynos4210_power_off,
+ },
+ {
+ .label = "hsic1",
+ .id = EXYNOS4210_HSIC1,
+ .power_on = exynos4210_power_on,
+ .power_off = exynos4210_power_off,
+ },
+ {},
+};
+
+- int (*power_on)(struct samsung_usb2_phy_instance *);
+- int (*power_off)(struct samsung_usb2_phy_instance *);
+ These two callbacks are used to power on and power off the phy
+ by modifying appropriate registers.
+
+Final change to the driver is adding appropriate compatible value to the
+phy-samsung-usb2.c file. In case of Exynos 4210 the following lines were
+added to the struct of_device_id samsung_usb2_phy_of_match[] array:
+
+#ifdef CONFIG_PHY_EXYNOS4210_USB2
+ {
+ .compatible = "samsung,exynos4210-usb2-phy",
+ .data = &exynos4210_usb2_phy_config,
+ },
+#endif
+
+To add further flexibility to the driver the Kconfig file enables to
+include support for selected SoCs in the compiled driver. The Kconfig
+entry for Exynos 4210 is following:
+
+config PHY_EXYNOS4210_USB2
+ bool "Support for Exynos 4210"
+ depends on PHY_SAMSUNG_USB2
+ depends on CPU_EXYNOS4210
+ help
+ Enable USB PHY support for Exynos 4210. This option requires that
+ Samsung USB 2.0 PHY driver is enabled and means that support for this
+ particular SoC is compiled in the driver. In case of Exynos 4210 four
+ phys are available - device, host, HSCI0 and HSCI1.
+
+The newly created file that supports the new SoC has to be also added to the
+Makefile. In case of Exynos 4210 the added line is following:
+
+obj-$(CONFIG_PHY_EXYNOS4210_USB2) += phy-exynos4210-usb2.o
+
+After completing these steps the support for the new SoC should be ready.
Code Review / kvmfornfv.git / blobdiff