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This patch contains UDM-design.txt, which is document containing general description of the driver model. The remaining files contains descriptions of conversion process of particular subsystems. Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
192 lines
7.2 KiB
Plaintext
192 lines
7.2 KiB
Plaintext
The U-Boot Driver Model Project
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===============================
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I/O system analysis
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===================
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Marek Vasut <marek.vasut@gmail.com>
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2012-02-20
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I) Overview
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-----------
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The console input and output is currently done using the STDIO subsystem in
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U-Boot. The design of this subsystem is already flexible enough to be easily
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converted to new driver model approach. Minor changes will need to be done
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though.
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Each device that wants to register with STDIO subsystem has to define struct
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stdio_dev, defined in include/stdio_dev.h and containing the following fields:
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struct stdio_dev {
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int flags; /* Device flags: input/output/system */
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int ext; /* Supported extensions */
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char name[16]; /* Device name */
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/* GENERAL functions */
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int (*start) (void); /* To start the device */
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int (*stop) (void); /* To stop the device */
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/* OUTPUT functions */
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void (*putc) (const char c); /* To put a char */
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void (*puts) (const char *s); /* To put a string (accelerator) */
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/* INPUT functions */
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int (*tstc) (void); /* To test if a char is ready... */
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int (*getc) (void); /* To get that char */
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/* Other functions */
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void *priv; /* Private extensions */
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struct list_head list;
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};
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Currently used flags are DEV_FLAGS_INPUT, DEV_FLAGS_OUTPUT and DEV_FLAGS_SYSTEM,
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extensions being only one, the DEV_EXT_VIDEO.
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The private extensions are now used as a per-device carrier of private data and
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finally list allows this structure to be a member of linked list of STDIO
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devices.
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The STDIN, STDOUT and STDERR routing is handled by environment variables
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"stdin", "stdout" and "stderr". By configuring the variable to the name of a
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driver, functions of such driver are called to execute that particular
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operation.
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II) Approach
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------------
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1) Similarity of serial, video and keyboard drivers
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---------------------------------------------------
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All of these drivers can be unified under the STDIO subsystem if modified
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slightly. The serial drivers basically define both input and output functions
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and need function to configure baudrate. The keyboard drivers provide only
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input. On the other hand, video drivers provide output, but need to be
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configured in certain way. This configuration might be dynamic, therefore the
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STDIO has to be modified to provide such flexibility.
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2) Unification of serial, video and keyboard drivers
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----------------------------------------------------
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Every STDIO device would register a structure containing operation it supports
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with the STDIO core by calling:
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int stdio_device_register(struct instance *i, struct stdio_device_ops *o);
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The structure being defined as follows:
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struct stdio_device_ops {
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void (*putc)(struct instance *i, const char c);
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void (*puts)(struct instance *i, const char *s); /* OPTIONAL */
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int (*tstc)(struct instance *i);
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int (*getc)(struct instance *i);
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int (*init)(struct instance *i);
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int (*exit)(struct instance *i);
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int (*conf)(struct instance *i, enum stdio_config c, const void *data);
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};
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The "putc()" function will emit a character, the "puts()" function will emit a
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string. If both of these are set to NULL, the device is considered STDIN only,
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aka input only device.
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The "getc()" retrieves a character from a STDIN device, while "tstc()" tests
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if there is a character in the buffer of STDIN device. In case these two are
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set to NULL, this device is STDOUT / STDERR device.
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Setting all "putc()", "puts()", "getc()" and "tstc()" calls to NULL isn't an
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error condition, though such device does nothing. By instroducing tests for
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these functions being NULL, the "flags" and "ext" fields from original struct
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stdio_dev can be eliminated.
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The "init()" and "exit()" calls are replacement for "start()" and "exit()"
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calls in the old approach. The "priv" part of the old struct stdio_dev will be
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replaced by common private data in the driver model and the struct list_head
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list will be eliminated by introducing common STDIO core, that tracks all the
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STDIO devices.
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Lastly, the "conf()" call will allow the user to configure various options of
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the driver. The enum stdio_config contains all possible configuration options
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available to the STDIO devices, const void *data being the argument to be
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configured. Currently, the enum stdio_config will contain at least the
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following options:
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enum stdio_config {
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STDIO_CONFIG_SERIAL_BAUDRATE,
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};
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3) Transformation of stdio routing
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----------------------------------
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By allowing multiple instances of drivers, the environment variables "stdin",
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"stdout" and "stderr" can no longer be set to the name of the driver.
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Therefore the STDIO core, tracking all of the STDIO devices in the system will
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need to have a small amount of internal data for each device:
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struct stdio_device_node {
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struct instance *i;
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struct stdio_device_ops *ops;
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uint8_t id;
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uint8_t flags;
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struct list_head list;
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}
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The "id" is the order of the instance of the same driver. The "flags" variable
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allows multiple drivers to be used at the same time and even for different
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purpose. The following flags will be defined:
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STDIO_FLG_STDIN ..... This device will be used as an input device. All input
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from all devices with this flag set will be received
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and passed to the upper layers.
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STDIO_FLG_STDOUT .... This device will be used as an output device. All
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output sent to stdout will be routed to all devices
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with this flag set.
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STDIO_FLG_STDERR .... This device will be used as an standard error output
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device. All output sent to stderr will be routed to
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all devices with this flag set.
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The "list" member of this structure allows to have a linked list of all
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registered STDIO devices.
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III) Analysis of in-tree drivers
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--------------------------------
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For in-depth analysis of serial port drivers, refer to [ UDM-serial.txt ].
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For in-depth analysis of keyboard drivers, refer to [ UDM-keyboard.txt ].
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For in-depth analysis of video drivers, refer to [ UDM-video.txt ].
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1) arch/blackfin/cpu/jtag-console.c
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-----------------------------------
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This driver is a classic STDIO driver, no problem with conversion is expected.
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2) board/mpl/pati/pati.c
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------------------------
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This driver registers with the STDIO framework, though it uses a lot of ad-hoc
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stuff which will need to be sorted out.
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3) board/netphone/phone_console.c
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---------------------------------
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This driver is a classic STDIO driver, no problem with conversion is expected.
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4) drivers/net/netconsole.c
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---------------------------
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This driver is a classic STDIO driver, no problem with conversion is expected.
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IV) Other involved files (To be removed)
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----------------------------------------
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common/cmd_console.c
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common/cmd_log.c
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common/cmd_terminal.c
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common/console.c
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common/fdt_support.c
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common/iomux.c
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common/lcd.c
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common/serial.c
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common/stdio.c
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common/usb_kbd.c
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doc/README.iomux
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