docs: phy: convert samsung-usb2.txt to ReST format
In order to merge it into a Sphinx book, we need first to convert to ReST. While this is not part of any book, mark it as :orphan:, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>alistair/sunxi64-5.4-dsi
Mauro Carvalho Chehab
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@ -1,9 +1,11 @@
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.------------------------------------------------------------------------------+
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| Samsung USB 2.0 PHY adaptation layer |
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+-----------------------------------------------------------------------------+'
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:orphan:
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| 1. Description
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+----------------
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====================================
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Samsung USB 2.0 PHY adaptation layer
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====================================
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1. Description
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--------------
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The architecture of the USB 2.0 PHY module in Samsung SoCs is similar
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among many SoCs. In spite of the similarities it proved difficult to
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@ -14,8 +16,8 @@ the PHY powering up process had to be altered. This adaptation layer is
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a compromise between having separate drivers and having a single driver
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with added support for many special cases.
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| 2. Files description
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+----------------------
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2. Files description
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--------------------
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- phy-samsung-usb2.c
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This is the main file of the adaptation layer. This file contains
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@ -32,44 +34,45 @@ with added support for many special cases.
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driver. In addition it should contain extern declarations for
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structures that describe particular SoCs.
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| 3. Supporting SoCs
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+--------------------
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3. Supporting SoCs
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------------------
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To support a new SoC a new file should be added to the drivers/phy
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directory. Each SoC's configuration is stored in an instance of the
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struct samsung_usb2_phy_config.
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struct samsung_usb2_phy_config::
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struct samsung_usb2_phy_config {
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struct samsung_usb2_phy_config {
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const struct samsung_usb2_common_phy *phys;
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int (*rate_to_clk)(unsigned long, u32 *);
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unsigned int num_phys;
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bool has_mode_switch;
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};
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};
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The num_phys is the number of phys handled by the driver. *phys is an
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The num_phys is the number of phys handled by the driver. `*phys` is an
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array that contains the configuration for each phy. The has_mode_switch
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property is a boolean flag that determines whether the SoC has USB host
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and device on a single pair of pins. If so, a special register has to
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be modified to change the internal routing of these pins between a USB
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device or host module.
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For example the configuration for Exynos 4210 is following:
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For example the configuration for Exynos 4210 is following::
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const struct samsung_usb2_phy_config exynos4210_usb2_phy_config = {
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const struct samsung_usb2_phy_config exynos4210_usb2_phy_config = {
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.has_mode_switch = 0,
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.num_phys = EXYNOS4210_NUM_PHYS,
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.phys = exynos4210_phys,
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.rate_to_clk = exynos4210_rate_to_clk,
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}
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}
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- `int (*rate_to_clk)(unsigned long, u32 *)`
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- int (*rate_to_clk)(unsigned long, u32 *)
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The rate_to_clk callback is to convert the rate of the clock
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used as the reference clock for the PHY module to the value
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that should be written in the hardware register.
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The exynos4210_phys configuration array is as follows:
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The exynos4210_phys configuration array is as follows::
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static const struct samsung_usb2_common_phy exynos4210_phys[] = {
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static const struct samsung_usb2_common_phy exynos4210_phys[] = {
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{
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.label = "device",
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.id = EXYNOS4210_DEVICE,
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@ -95,29 +98,30 @@ static const struct samsung_usb2_common_phy exynos4210_phys[] = {
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.power_off = exynos4210_power_off,
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},
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{},
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};
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};
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- `int (*power_on)(struct samsung_usb2_phy_instance *);`
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`int (*power_off)(struct samsung_usb2_phy_instance *);`
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- int (*power_on)(struct samsung_usb2_phy_instance *);
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- int (*power_off)(struct samsung_usb2_phy_instance *);
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These two callbacks are used to power on and power off the phy
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by modifying appropriate registers.
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Final change to the driver is adding appropriate compatible value to the
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phy-samsung-usb2.c file. In case of Exynos 4210 the following lines were
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added to the struct of_device_id samsung_usb2_phy_of_match[] array:
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added to the struct of_device_id samsung_usb2_phy_of_match[] array::
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#ifdef CONFIG_PHY_EXYNOS4210_USB2
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#ifdef CONFIG_PHY_EXYNOS4210_USB2
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{
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.compatible = "samsung,exynos4210-usb2-phy",
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.data = &exynos4210_usb2_phy_config,
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},
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#endif
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#endif
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To add further flexibility to the driver the Kconfig file enables to
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include support for selected SoCs in the compiled driver. The Kconfig
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entry for Exynos 4210 is following:
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entry for Exynos 4210 is following::
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config PHY_EXYNOS4210_USB2
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config PHY_EXYNOS4210_USB2
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bool "Support for Exynos 4210"
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depends on PHY_SAMSUNG_USB2
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depends on CPU_EXYNOS4210
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@ -128,8 +132,8 @@ config PHY_EXYNOS4210_USB2
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phys are available - device, host, HSCI0 and HSCI1.
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The newly created file that supports the new SoC has to be also added to the
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Makefile. In case of Exynos 4210 the added line is following:
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Makefile. In case of Exynos 4210 the added line is following::
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obj-$(CONFIG_PHY_EXYNOS4210_USB2) += phy-exynos4210-usb2.o
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obj-$(CONFIG_PHY_EXYNOS4210_USB2) += phy-exynos4210-usb2.o
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After completing these steps the support for the new SoC should be ready.
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@ -14083,7 +14083,7 @@ M: Sylwester Nawrocki <s.nawrocki@samsung.com>
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L: linux-kernel@vger.kernel.org
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S: Supported
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F: Documentation/devicetree/bindings/phy/samsung-phy.txt
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F: Documentation/phy/samsung-usb2.txt
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F: Documentation/phy/samsung-usb2.rst
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F: drivers/phy/samsung/phy-exynos4210-usb2.c
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F: drivers/phy/samsung/phy-exynos4x12-usb2.c
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F: drivers/phy/samsung/phy-exynos5250-usb2.c
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