diff options
72 files changed, 4122 insertions, 787 deletions
diff --git a/Documentation/ABI/testing/configfs-usb-gadget b/Documentation/ABI/testing/configfs-usb-gadget index 37559a06393..95a36589a66 100644 --- a/Documentation/ABI/testing/configfs-usb-gadget +++ b/Documentation/ABI/testing/configfs-usb-gadget @@ -62,6 +62,40 @@ KernelVersion: 3.11 Description: This group contains functions available to this USB gadget. +What: /config/usb-gadget/gadget/functions/<func>.<inst>/interface.<n> +Date: May 2014 +KernelVersion: 3.16 +Description: + This group contains "Feature Descriptors" specific for one + gadget's USB interface or one interface group described + by an IAD. + + The attributes: + + compatible_id - 8-byte string for "Compatible ID" + sub_compatible_id - 8-byte string for "Sub Compatible ID" + +What: /config/usb-gadget/gadget/functions/<func>.<inst>/interface.<n>/<property> +Date: May 2014 +KernelVersion: 3.16 +Description: + This group contains "Extended Property Descriptors" specific for one + gadget's USB interface or one interface group described + by an IAD. + + The attributes: + + type - value 1..7 for interpreting the data + 1: unicode string + 2: unicode string with environment variable + 3: binary + 4: little-endian 32-bit + 5: big-endian 32-bit + 6: unicode string with a symbolic link + 7: multiple unicode strings + data - blob of data to be interpreted depending on + type + What: /config/usb-gadget/gadget/strings Date: Jun 2013 KernelVersion: 3.11 @@ -79,3 +113,14 @@ Description: product - gadget's product description manufacturer - gadget's manufacturer description +What: /config/usb-gadget/gadget/os_desc +Date: May 2014 +KernelVersion: 3.16 +Description: + This group contains "OS String" extension handling attributes. + + use - flag turning "OS Desctiptors" support on/off + b_vendor_code - one-byte value used for custom per-device and + per-interface requests + qw_sign - an identifier to be reported as "OS String" + proper diff --git a/Documentation/DocBook/Makefile b/Documentation/DocBook/Makefile index b444f2e8fe3..bec06659e0e 100644 --- a/Documentation/DocBook/Makefile +++ b/Documentation/DocBook/Makefile @@ -14,7 +14,8 @@ DOCBOOKS := z8530book.xml device-drivers.xml \ genericirq.xml s390-drivers.xml uio-howto.xml scsi.xml \ 80211.xml debugobjects.xml sh.xml regulator.xml \ alsa-driver-api.xml writing-an-alsa-driver.xml \ - tracepoint.xml drm.xml media_api.xml w1.xml + tracepoint.xml drm.xml media_api.xml w1.xml \ + writing_musb_glue_layer.xml include Documentation/DocBook/media/Makefile diff --git a/Documentation/DocBook/writing_musb_glue_layer.tmpl b/Documentation/DocBook/writing_musb_glue_layer.tmpl new file mode 100644 index 00000000000..837eca77f27 --- /dev/null +++ b/Documentation/DocBook/writing_musb_glue_layer.tmpl @@ -0,0 +1,873 @@ +<?xml version="1.0" encoding="UTF-8"?> +<!DOCTYPE book PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN" + "http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd" []> + +<book id="Writing-MUSB-Glue-Layer"> + <bookinfo> + <title>Writing an MUSB Glue Layer</title> + + <authorgroup> + <author> + <firstname>Apelete</firstname> + <surname>Seketeli</surname> + <affiliation> + <address> + <email>apelete at seketeli.net</email> + </address> + </affiliation> + </author> + </authorgroup> + + <copyright> + <year>2014</year> + <holder>Apelete Seketeli</holder> + </copyright> + + <legalnotice> + <para> + This documentation is free software; you can redistribute it + and/or modify it under the terms of the GNU General Public + License as published by the Free Software Foundation; either + version 2 of the License, or (at your option) any later version. + </para> + + <para> + This documentation is distributed in the hope that it will be + useful, but WITHOUT ANY WARRANTY; without even the implied + warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. + See the GNU General Public License for more details. + </para> + + <para> + You should have received a copy of the GNU General Public License + along with this documentation; if not, write to the Free Software + Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA + 02111-1307 USA + </para> + + <para> + For more details see the file COPYING in the Linux kernel source + tree. + </para> + </legalnotice> + </bookinfo> + +<toc></toc> + + <chapter id="introduction"> + <title>Introduction</title> + <para> + The Linux MUSB subsystem is part of the larger Linux USB + subsystem. It provides support for embedded USB Device Controllers + (UDC) that do not use Universal Host Controller Interface (UHCI) + or Open Host Controller Interface (OHCI). + </para> + <para> + Instead, these embedded UDC rely on the USB On-the-Go (OTG) + specification which they implement at least partially. The silicon + reference design used in most cases is the Multipoint USB + Highspeed Dual-Role Controller (MUSB HDRC) found in the Mentor + Graphics Inventra™ design. + </para> + <para> + As a self-taught exercise I have written an MUSB glue layer for + the Ingenic JZ4740 SoC, modelled after the many MUSB glue layers + in the kernel source tree. This layer can be found at + drivers/usb/musb/jz4740.c. In this documentation I will walk + through the basics of the jz4740.c glue layer, explaining the + different pieces and what needs to be done in order to write your + own device glue layer. + </para> + </chapter> + + <chapter id="linux-musb-basics"> + <title>Linux MUSB Basics</title> + <para> + To get started on the topic, please read USB On-the-Go Basics (see + Resources) which provides an introduction of USB OTG operation at + the hardware level. A couple of wiki pages by Texas Instruments + and Analog Devices also provide an overview of the Linux kernel + MUSB configuration, albeit focused on some specific devices + provided by these companies. Finally, getting acquainted with the + USB specification at USB home page may come in handy, with + practical instance provided through the Writing USB Device Drivers + documentation (again, see Resources). + </para> + <para> + Linux USB stack is a layered architecture in which the MUSB + controller hardware sits at the lowest. The MUSB controller driver + abstract the MUSB controller hardware to the Linux USB stack. + </para> + <programlisting> + ------------------------ + | | <------- drivers/usb/gadget + | Linux USB Core Stack | <------- drivers/usb/host + | | <------- drivers/usb/core + ------------------------ + ⬍ + -------------------------- + | | <------ drivers/usb/musb/musb_gadget.c + | MUSB Controller driver | <------ drivers/usb/musb/musb_host.c + | | <------ drivers/usb/musb/musb_core.c + -------------------------- + ⬍ + --------------------------------- + | MUSB Platform Specific Driver | + | | <-- drivers/usb/musb/jz4740.c + | aka "Glue Layer" | + --------------------------------- + ⬍ + --------------------------------- + | MUSB Controller Hardware | + --------------------------------- + </programlisting> + <para> + As outlined above, the glue layer is actually the platform + specific code sitting in between the controller driver and the + controller hardware. + </para> + <para> + Just like a Linux USB driver needs to register itself with the + Linux USB subsystem, the MUSB glue layer needs first to register + itself with the MUSB controller driver. This will allow the + controller driver to know about which device the glue layer + supports and which functions to call when a supported device is + detected or released; remember we are talking about an embedded + controller chip here, so no insertion or removal at run-time. + </para> + <para> + All of this information is passed to the MUSB controller driver + through a platform_driver structure defined in the glue layer as: + </para> + <programlisting linenumbering="numbered"> +static struct platform_driver jz4740_driver = { + .probe = jz4740_probe, + .remove = jz4740_remove, + .driver = { + .name = "musb-jz4740", + }, +}; + </programlisting> + <para> + The probe and remove function pointers are called when a matching + device is detected and, respectively, released. The name string + describes the device supported by this glue layer. In the current + case it matches a platform_device structure declared in + arch/mips/jz4740/platform.c. Note that we are not using device + tree bindings here. + </para> + <para> + In order to register itself to the controller driver, the glue + layer goes through a few steps, basically allocating the + controller hardware resources and initialising a couple of + circuits. To do so, it needs to keep track of the information used + throughout these steps. This is done by defining a private + jz4740_glue structure: + </para> + <programlisting linenumbering="numbered"> +struct jz4740_glue { + struct device *dev; + struct platform_device *musb; + struct clk *clk; +}; + </programlisting> + <para> + The dev and musb members are both device structure variables. The + first one holds generic information about the device, since it's + the basic device structure, and the latter holds information more + closely related to the subsystem the device is registered to. The + clk variable keeps information related to the device clock + operation. + </para> + <para> + Let's go through the steps of the probe function that leads the + glue layer to register itself to the controller driver. + </para> + <para> + N.B.: For the sake of readability each function will be split in + logical parts, each part being shown as if it was independent from + the others. + </para> + <programlisting linenumbering="numbered"> +static int jz4740_probe(struct platform_device *pdev) +{ + struct platform_device *musb; + struct jz4740_glue *glue; + struct clk *clk; + int ret; + + glue = devm_kzalloc(&pdev->dev, sizeof(*glue), GFP_KERNEL); + if (!glue) + return -ENOMEM; + + musb = platform_device_alloc("musb-hdrc", PLATFORM_DEVID_AUTO); + if (!musb) { + dev_err(&pdev->dev, "failed to allocate musb device\n"); + return -ENOMEM; + } + + clk = devm_clk_get(&pdev->dev, "udc"); + if (IS_ERR(clk)) { + dev_err(&pdev->dev, "failed to get clock\n"); + ret = PTR_ERR(clk); + goto err_platform_device_put; + } + + ret = clk_prepare_enable(clk); + if (ret) { + dev_err(&pdev->dev, "failed to enable clock\n"); + goto err_platform_device_put; + } + + musb->dev.parent = &pdev->dev; + + glue->dev = &pdev->dev; + glue->musb = musb; + glue->clk = clk; + + return 0; + +err_platform_device_put: + platform_device_put(musb); + return ret; +} + </programlisting> + <para> + The first few lines of the probe function allocate and assign the + glue, musb and clk variables. The GFP_KERNEL flag (line 8) allows + the allocation process to sleep and wait for memory, thus being + usable in a blocking situation. The PLATFORM_DEVID_AUTO flag (line + 12) allows automatic allocation and management of device IDs in + order to avoid device namespace collisions with explicit IDs. With + devm_clk_get() (line 18) the glue layer allocates the clock -- the + <literal>devm_</literal> prefix indicates that clk_get() is + managed: it automatically frees the allocated clock resource data + when the device is released -- and enable it. + </para> + <para> + Then comes the registration steps: + </para> + <programlisting linenumbering="numbered"> +static int jz4740_probe(struct platform_device *pdev) +{ + struct musb_hdrc_platform_data *pdata = &jz4740_musb_platform_data; + + pdata->platform_ops = &jz4740_musb_ops; + + platform_set_drvdata(pdev, glue); + + ret = platform_device_add_resources(musb, pdev->resource, + pdev->num_resources); + if (ret) { + dev_err(&pdev->dev, "failed to add resources\n"); + goto err_clk_disable; + } + + ret = platform_device_add_data(musb, pdata, sizeof(*pdata)); + if (ret) { + dev_err(&pdev->dev, "failed to add platform_data\n"); + goto err_clk_disable; + } + + return 0; + +err_clk_disable: + clk_disable_unprepare(clk); +err_platform_device_put: + platform_device_put(musb); + return ret; +} + </programlisting> + <para> + The first step is to pass the device data privately held by the + glue layer on to the controller driver through + platform_set_drvdata() (line 7). Next is passing on the device + resources information, also privately held at that point, through + platform_device_add_resources() (line 9). + </para> + <para> + Finally comes passing on the platform specific data to the + controller driver (line 16). Platform data will be discussed in + <link linkend="device-platform-data">Chapter 4</link>, but here + we are looking at the platform_ops function pointer (line 5) in + musb_hdrc_platform_data structure (line 3). This function + pointer allows the MUSB controller driver to know which function + to call for device operation: + </para> + <programlisting linenumbering="numbered"> +static const struct musb_platform_ops jz4740_musb_ops = { + .init = jz4740_musb_init, + .exit = jz4740_musb_exit, +}; + </programlisting> + <para> + Here we have the minimal case where only init and exit functions + are called by the controller driver when needed. Fact is the + JZ4740 MUSB controller is a basic controller, lacking some + features found in other controllers, otherwise we may also have + pointers to a few other functions like a power management function + or a function to switch between OTG and non-OTG modes, for + instance. + </para> + <para> + At that point of the registration process, the controller driver + actually calls the init function: + </para> + <programlisting linenumbering="numbered"> +static int jz4740_musb_init(struct musb *musb) +{ + musb->xceiv = usb_get_phy(USB_PHY_TYPE_USB2); + if (!musb->xceiv) { + pr_err("HS UDC: no transceiver configured\n"); + return -ENODEV; + } + + /* Silicon does not implement ConfigData register. + * Set dyn_fifo to avoid reading EP config from hardware. + */ + musb->dyn_fifo = true; + + musb->isr = jz4740_musb_interrupt; + + return 0; +} + </programlisting> + <para> + The goal of jz4740_musb_init() is to get hold of the transceiver + driver data of the MUSB controller hardware and pass it on to the + MUSB controller driver, as usual. The transceiver is the circuitry + inside the controller hardware responsible for sending/receiving + the USB data. Since it is an implementation of the physical layer + of the OSI model, the transceiver is also referred to as PHY. + </para> + <para> + Getting hold of the MUSB PHY driver data is done with + usb_get_phy() which returns a pointer to the structure + containing the driver instance data. The next couple of + instructions (line 12 and 14) are used as a quirk and to setup + IRQ handling respectively. Quirks and IRQ handling will be + discussed later in <link linkend="device-quirks">Chapter + 5</link> and <link linkend="handling-irqs">Chapter 3</link>. + </para> + <programlisting linenumbering="numbered"> +static int jz4740_musb_exit(struct musb *musb) +{ + usb_put_phy(musb->xceiv); + + return 0; +} + </programlisting> + <para> + Acting as the counterpart of init, the exit function releases the + MUSB PHY driver when the controller hardware itself is about to be + released. + </para> + <para> + Again, note that init and exit are fairly simple in this case due + to the basic set of features of the JZ4740 controller hardware. + When writing an musb glue layer for a more complex controller + hardware, you might need to take care of more processing in those + two functions. + </para> + <para> + Returning from the init function, the MUSB controller driver jumps + back into the probe function: + </para> + <programlisting linenumbering="numbered"> +static int jz4740_probe(struct platform_device *pdev) +{ + ret = platform_device_add(musb); + if (ret) { + dev_err(&pdev->dev, "failed to register musb device\n"); + goto err_clk_disable; + } + + return 0; + +err_clk_disable: + clk_disable_unprepare(clk); +err_platform_device_put: + platform_device_put(musb); + return ret; +} + </programlisting> + <para> + This is the last part of the device registration process where the + glue layer adds the controller hardware device to Linux kernel + device hierarchy: at this stage, all known information about the + device is passed on to the Linux USB core stack. + </para> + <programlisting linenumbering="numbered"> +static int jz4740_remove(struct platform_device *pdev) +{ + struct jz4740_glue *glue = platform_get_drvdata(pdev); + + platform_device_unregister(glue->musb); + clk_disable_unprepare(glue->clk); + + return 0; +} + </programlisting> + <para> + Acting as the counterpart of probe, the remove function unregister + the MUSB controller hardware (line 5) and disable the clock (line + 6), allowing it to be gated. + </para> + </chapter> + + <chapter id="handling-irqs"> + <title>Handling IRQs</title> + <para> + Additionally to the MUSB controller hardware basic setup and + registration, the glue layer is also responsible for handling the + IRQs: + </para> + <programlisting linenumbering="numbered"> +static irqreturn_t jz4740_musb_interrupt(int irq, void *__hci) +{ + unsigned long flags; + irqreturn_t retval = IRQ_NONE; + s |