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authorLinus Torvalds <torvalds@linux-foundation.org>2013-11-07 09:19:48 +0900
committerLinus Torvalds <torvalds@linux-foundation.org>2013-11-07 09:19:48 +0900
commitc287322c3aadf45ee15339bffdbc2e9117b9cc7a (patch)
tree47e4a8583a9c8cb11186815760fb9e600e43449f /Documentation
parentbe408cd3e1fef73e9408b196a79b9934697fe3b1 (diff)
parent7d49f0bac41ee9b012af1efe2f725d91a87a8fe9 (diff)
downloadlinux-c287322c3aadf45ee15339bffdbc2e9117b9cc7a.tar.bz2
Merge tag 'usb-3.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb
Pull USB driver update from Greg KH: "Here's the big USB driver update for 3.13-rc1. It includes the usual xhci changes, EHCI updates to get the scheduling of USB transactions working better, and a raft of gadget and musb updates as well. All of this has been in linux-next for a while with no reported issues" * tag 'usb-3.13-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb: (305 commits) USB: Maintainers change for usb serial drivers usb: usbtest: support container id descriptor test usb: usbtest: support superspeed device capbility descriptor test usb: usbtest: support usb2 extension descriptor test usb: chipidea: only get vbus regulator for non-peripheral mode USB: ehci-atmel: add usb_clk for transition to CCF usb: cdc-wdm: ignore speed change notifications USB: cdc-wdm: support back-to-back USB_CDC_NOTIFY_RESPONSE_AVAILABLE notifications usbatm: Fix dynamic_debug / ratelimited atm_dbg and atm_rldbg macros printk: pr_debug_ratelimited: check state first to reduce "callbacks suppressed" messages usb: usbtest: support bos descriptor test for usb 3.0 USB: phy: samsung: Support multiple PHYs of same type usb: wusbcore: change WA_SEGS_MAX to a legal value usb: wusbcore: add a quirk for Alereon HWA device isoc behavior usb: wusbcore: combine multiple isoc frames in a single transfer request. usb: wusbcore: set the RPIPE wMaxPacketSize value correctly usb: chipidea: host: more enhancement when ci->hcd is NULL usb: ohci: remove ep93xx bus glue platform driver usb: usbtest: fix checkpatch warning as sizeof code style UWB: clean up attribute use by using ATTRIBUTE_GROUPS() ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/ABI/testing/configfs-usb-gadget-mass-storage31
-rw-r--r--Documentation/devicetree/bindings/phy/phy-bindings.txt66
-rw-r--r--Documentation/devicetree/bindings/phy/samsung-phy.txt22
-rw-r--r--Documentation/devicetree/bindings/usb/msm-hsusb.txt17
-rw-r--r--Documentation/devicetree/bindings/usb/omap-usb.txt39
-rw-r--r--Documentation/devicetree/bindings/usb/usb-nop-xceiv.txt7
-rw-r--r--Documentation/devicetree/bindings/usb/usb-phy.txt6
-rw-r--r--Documentation/devicetree/bindings/video/exynos_dp.txt17
-rw-r--r--Documentation/phy.txt166
-rw-r--r--Documentation/pps/pps.txt15
10 files changed, 355 insertions, 31 deletions
diff --git a/Documentation/ABI/testing/configfs-usb-gadget-mass-storage b/Documentation/ABI/testing/configfs-usb-gadget-mass-storage
new file mode 100644
index 000000000000..ad72a37ee9ff
--- /dev/null
+++ b/Documentation/ABI/testing/configfs-usb-gadget-mass-storage
@@ -0,0 +1,31 @@
+What: /config/usb-gadget/gadget/functions/mass_storage.name
+Date: Oct 2013
+KenelVersion: 3.13
+Description:
+ The attributes:
+
+ stall - Set to permit function to halt bulk endpoints.
+ Disabled on some USB devices known not to work
+ correctly. You should set it to true.
+ num_buffers - Number of pipeline buffers. Valid numbers
+ are 2..4. Available only if
+ CONFIG_USB_GADGET_DEBUG_FILES is set.
+
+What: /config/usb-gadget/gadget/functions/mass_storage.name/lun.name
+Date: Oct 2013
+KenelVersion: 3.13
+Description:
+ The attributes:
+
+ file - The path to the backing file for the LUN.
+ Required if LUN is not marked as removable.
+ ro - Flag specifying access to the LUN shall be
+ read-only. This is implied if CD-ROM emulation
+ is enabled as well as when it was impossible
+ to open "filename" in R/W mode.
+ removable - Flag specifying that LUN shall be indicated as
+ being removable.
+ cdrom - Flag specifying that LUN shall be reported as
+ being a CD-ROM.
+ nofua - Flag specifying that FUA flag
+ in SCSI WRITE(10,12)
diff --git a/Documentation/devicetree/bindings/phy/phy-bindings.txt b/Documentation/devicetree/bindings/phy/phy-bindings.txt
new file mode 100644
index 000000000000..8ae844fc0c60
--- /dev/null
+++ b/Documentation/devicetree/bindings/phy/phy-bindings.txt
@@ -0,0 +1,66 @@
+This document explains only the device tree data binding. For general
+information about PHY subsystem refer to Documentation/phy.txt
+
+PHY device node
+===============
+
+Required Properties:
+#phy-cells: Number of cells in a PHY specifier; The meaning of all those
+ cells is defined by the binding for the phy node. The PHY
+ provider can use the values in cells to find the appropriate
+ PHY.
+
+For example:
+
+phys: phy {
+ compatible = "xxx";
+ reg = <...>;
+ .
+ .
+ #phy-cells = <1>;
+ .
+ .
+};
+
+That node describes an IP block (PHY provider) that implements 2 different PHYs.
+In order to differentiate between these 2 PHYs, an additonal specifier should be
+given while trying to get a reference to it.
+
+PHY user node
+=============
+
+Required Properties:
+phys : the phandle for the PHY device (used by the PHY subsystem)
+phy-names : the names of the PHY corresponding to the PHYs present in the
+ *phys* phandle
+
+Example 1:
+usb1: usb_otg_ss@xxx {
+ compatible = "xxx";
+ reg = <xxx>;
+ .
+ .
+ phys = <&usb2_phy>, <&usb3_phy>;
+ phy-names = "usb2phy", "usb3phy";
+ .
+ .
+};
+
+This node represents a controller that uses two PHYs, one for usb2 and one for
+usb3.
+
+Example 2:
+usb2: usb_otg_ss@xxx {
+ compatible = "xxx";
+ reg = <xxx>;
+ .
+ .
+ phys = <&phys 1>;
+ phy-names = "usbphy";
+ .
+ .
+};
+
+This node represents a controller that uses one of the PHYs of the PHY provider
+device defined previously. Note that the phy handle has an additional specifier
+"1" to differentiate between the two PHYs.
diff --git a/Documentation/devicetree/bindings/phy/samsung-phy.txt b/Documentation/devicetree/bindings/phy/samsung-phy.txt
new file mode 100644
index 000000000000..c0fccaa1671e
--- /dev/null
+++ b/Documentation/devicetree/bindings/phy/samsung-phy.txt
@@ -0,0 +1,22 @@
+Samsung S5P/EXYNOS SoC series MIPI CSIS/DSIM DPHY
+-------------------------------------------------
+
+Required properties:
+- compatible : should be "samsung,s5pv210-mipi-video-phy";
+- reg : offset and length of the MIPI DPHY register set;
+- #phy-cells : from the generic phy bindings, must be 1;
+
+For "samsung,s5pv210-mipi-video-phy" compatible PHYs the second cell in
+the PHY specifier identifies the PHY and its meaning is as follows:
+ 0 - MIPI CSIS 0,
+ 1 - MIPI DSIM 0,
+ 2 - MIPI CSIS 1,
+ 3 - MIPI DSIM 1.
+
+Samsung EXYNOS SoC series Display Port PHY
+-------------------------------------------------
+
+Required properties:
+- compatible : should be "samsung,exynos5250-dp-video-phy";
+- reg : offset and length of the Display Port PHY register set;
+- #phy-cells : from the generic PHY bindings, must be 0;
diff --git a/Documentation/devicetree/bindings/usb/msm-hsusb.txt b/Documentation/devicetree/bindings/usb/msm-hsusb.txt
new file mode 100644
index 000000000000..5ea26c631e3a
--- /dev/null
+++ b/Documentation/devicetree/bindings/usb/msm-hsusb.txt
@@ -0,0 +1,17 @@
+MSM SoC HSUSB controllers
+
+EHCI
+
+Required properties:
+- compatible: Should contain "qcom,ehci-host"
+- regs: offset and length of the register set in the memory map
+- usb-phy: phandle for the PHY device
+
+Example EHCI controller device node:
+
+ ehci: ehci@f9a55000 {
+ compatible = "qcom,ehci-host";
+ reg = <0xf9a55000 0x400>;
+ usb-phy = <&usb_otg>;
+ };
+
diff --git a/Documentation/devicetree/bindings/usb/omap-usb.txt b/Documentation/devicetree/bindings/usb/omap-usb.txt
index 9088ab09e200..090e5e22bd2b 100644
--- a/Documentation/devicetree/bindings/usb/omap-usb.txt
+++ b/Documentation/devicetree/bindings/usb/omap-usb.txt
@@ -3,9 +3,6 @@ OMAP GLUE AND OTHER OMAP SPECIFIC COMPONENTS
OMAP MUSB GLUE
- compatible : Should be "ti,omap4-musb" or "ti,omap3-musb"
- ti,hwmods : must be "usb_otg_hs"
- - ti,has-mailbox : to specify that omap uses an external mailbox
- (in control module) to communicate with the musb core during device connect
- and disconnect.
- multipoint : Should be "1" indicating the musb controller supports
multipoint. This is a MUSB configuration-specific setting.
- num-eps : Specifies the number of endpoints. This is also a
@@ -19,6 +16,9 @@ OMAP MUSB GLUE
- power : Should be "50". This signifies the controller can supply up to
100mA when operating in host mode.
- usb-phy : the phandle for the PHY device
+ - phys : the phandle for the PHY device (used by generic PHY framework)
+ - phy-names : the names of the PHY corresponding to the PHYs present in the
+ *phy* phandle.
Optional properties:
- ctrl-module : phandle of the control module this glue uses to write to
@@ -28,11 +28,12 @@ SOC specific device node entry
usb_otg_hs: usb_otg_hs@4a0ab000 {
compatible = "ti,omap4-musb";
ti,hwmods = "usb_otg_hs";
- ti,has-mailbox;
multipoint = <1>;
num-eps = <16>;
ram-bits = <12>;
ctrl-module = <&omap_control_usb>;
+ phys = <&usb2_phy>;
+ phy-names = "usb2-phy";
};
Board specific device node entry
@@ -78,22 +79,22 @@ omap_dwc3 {
OMAP CONTROL USB
Required properties:
- - compatible: Should be "ti,omap-control-usb"
+ - compatible: Should be one of
+ "ti,control-phy-otghs" - if it has otghs_control mailbox register as on OMAP4.
+ "ti,control-phy-usb2" - if it has Power down bit in control_dev_conf register
+ e.g. USB2_PHY on OMAP5.
+ "ti,control-phy-pipe3" - if it has DPLL and individual Rx & Tx power control
+ e.g. USB3 PHY and SATA PHY on OMAP5.
+ "ti,control-phy-dra7usb2" - if it has power down register like USB2 PHY on
+ DRA7 platform.
- reg : Address and length of the register set for the device. It contains
- the address of "control_dev_conf" and "otghs_control" or "phy_power_usb"
- depending upon omap4 or omap5.
- - reg-names: The names of the register addresses corresponding to the registers
- filled in "reg".
- - ti,type: This is used to differentiate whether the control module has
- usb mailbox or usb3 phy power. omap4 has usb mailbox in control module to
- notify events to the musb core and omap5 has usb3 phy power register to
- power on usb3 phy. Should be "1" if it has mailbox and "2" if it has usb3
- phy power.
+ the address of "otghs_control" for control-phy-otghs or "power" register
+ for other types.
+ - reg-names: should be "otghs_control" control-phy-otghs and "power" for
+ other types.
omap_control_usb: omap-control-usb@4a002300 {
- compatible = "ti,omap-control-usb";
- reg = <0x4a002300 0x4>,
- <0x4a00233c 0x4>;
- reg-names = "control_dev_conf", "otghs_control";
- ti,type = <1>;
+ compatible = "ti,control-phy-otghs";
+ reg = <0x4a00233c 0x4>;
+ reg-names = "otghs_control";
};
diff --git a/Documentation/devicetree/bindings/usb/usb-nop-xceiv.txt b/Documentation/devicetree/bindings/usb/usb-nop-xceiv.txt
index d7e272671c7e..1bd37faba05b 100644
--- a/Documentation/devicetree/bindings/usb/usb-nop-xceiv.txt
+++ b/Documentation/devicetree/bindings/usb/usb-nop-xceiv.txt
@@ -15,7 +15,7 @@ Optional properties:
- vcc-supply: phandle to the regulator that provides RESET to the PHY.
-- reset-supply: phandle to the regulator that provides power to the PHY.
+- reset-gpios: Should specify the GPIO for reset.
Example:
@@ -25,10 +25,9 @@ Example:
clocks = <&osc 0>;
clock-names = "main_clk";
vcc-supply = <&hsusb1_vcc_regulator>;
- reset-supply = <&hsusb1_reset_regulator>;
+ reset-gpios = <&gpio1 7 GPIO_ACTIVE_LOW>;
};
hsusb1_phy is a NOP USB PHY device that gets its clock from an oscillator
and expects that clock to be configured to 19.2MHz by the NOP PHY driver.
-hsusb1_vcc_regulator provides power to the PHY and hsusb1_reset_regulator
-controls RESET.
+hsusb1_vcc_regulator provides power to the PHY and GPIO 7 controls RESET.
diff --git a/Documentation/devicetree/bindings/usb/usb-phy.txt b/Documentation/devicetree/bindings/usb/usb-phy.txt
index 61496f5cb095..c0245c888982 100644
--- a/Documentation/devicetree/bindings/usb/usb-phy.txt
+++ b/Documentation/devicetree/bindings/usb/usb-phy.txt
@@ -5,6 +5,8 @@ OMAP USB2 PHY
Required properties:
- compatible: Should be "ti,omap-usb2"
- reg : Address and length of the register set for the device.
+ - #phy-cells: determine the number of cells that should be given in the
+ phandle while referencing this phy.
Optional properties:
- ctrl-module : phandle of the control module used by PHY driver to power on
@@ -16,6 +18,7 @@ usb2phy@4a0ad080 {
compatible = "ti,omap-usb2";
reg = <0x4a0ad080 0x58>;
ctrl-module = <&omap_control_usb>;
+ #phy-cells = <0>;
};
OMAP USB3 PHY
@@ -25,6 +28,8 @@ Required properties:
- reg : Address and length of the register set for the device.
- reg-names: The names of the register addresses corresponding to the registers
filled in "reg".
+ - #phy-cells: determine the number of cells that should be given in the
+ phandle while referencing this phy.
Optional properties:
- ctrl-module : phandle of the control module used by PHY driver to power on
@@ -39,4 +44,5 @@ usb3phy@4a084400 {
<0x4a084c00 0x40>;
reg-names = "phy_rx", "phy_tx", "pll_ctrl";
ctrl-module = <&omap_control_usb>;
+ #phy-cells = <0>;
};
diff --git a/Documentation/devicetree/bindings/video/exynos_dp.txt b/Documentation/devicetree/bindings/video/exynos_dp.txt
index 84f10c16cb38..3289d76a21d0 100644
--- a/Documentation/devicetree/bindings/video/exynos_dp.txt
+++ b/Documentation/devicetree/bindings/video/exynos_dp.txt
@@ -6,10 +6,10 @@ We use two nodes:
-dptx-phy node(defined inside dp-controller node)
For the DP-PHY initialization, we use the dptx-phy node.
-Required properties for dptx-phy:
- -reg:
+Required properties for dptx-phy: deprecated, use phys and phy-names
+ -reg: deprecated
Base address of DP PHY register.
- -samsung,enable-mask:
+ -samsung,enable-mask: deprecated
The bit-mask used to enable/disable DP PHY.
For the Panel initialization, we read data from dp-controller node.
@@ -27,6 +27,10 @@ Required properties for dp-controller:
from common clock binding: Shall be "dp".
-interrupt-parent:
phandle to Interrupt combiner node.
+ -phys:
+ from general PHY binding: the phandle for the PHY device.
+ -phy-names:
+ from general PHY binding: Should be "dp".
-samsung,color-space:
input video data format.
COLOR_RGB = 0, COLOR_YCBCR422 = 1, COLOR_YCBCR444 = 2
@@ -68,11 +72,8 @@ SOC specific portion:
clocks = <&clock 342>;
clock-names = "dp";
- dptx-phy {
- reg = <0x10040720>;
- samsung,enable-mask = <1>;
- };
-
+ phys = <&dp_phy>;
+ phy-names = "dp";
};
Board Specific portion:
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
diff --git a/Documentation/pps/pps.txt b/Documentation/pps/pps.txt
index d35dcdd82ff6..c03b1be5eb15 100644
--- a/Documentation/pps/pps.txt
+++ b/Documentation/pps/pps.txt
@@ -66,6 +66,21 @@ In LinuxPPS the PPS sources are simply char devices usually mapped
into files /dev/pps0, /dev/pps1, etc..
+PPS with USB to serial devices
+------------------------------
+
+It is possible to grab the PPS from an USB to serial device. However,
+you should take into account the latencies and jitter introduced by
+the USB stack. Users has reported clock instability around +-1ms when
+synchronized with PPS through USB. This isn't suited for time server
+synchronization.
+
+If your device doesn't report PPS, you can check that the feature is
+supported by its driver. Most of the time, you only need to add a call
+to usb_serial_handle_dcd_change after checking the DCD status (see
+ch341 and pl2303 examples).
+
+
Coding example
--------------