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Diffstat (limited to 'doc/driver-model/UDM-serial.txt')
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diff --git a/doc/driver-model/UDM-serial.txt b/doc/driver-model/UDM-serial.txt new file mode 100644 index 00000000000..e9c274d451d --- /dev/null +++ b/doc/driver-model/UDM-serial.txt @@ -0,0 +1,191 @@ +The U-Boot Driver Model Project +=============================== +Serial I/O analysis +=================== +Marek Vasut <marek.vasut@gmail.com> +2012-02-20 + +I) Overview +----------- + +The serial port support currently requires the driver to export the following +functions: + + serial_putc() ...... Output a character + serial_puts() ...... Output string, often done using serial_putc() + serial_tstc() ...... Test if incoming character is in a buffer + serial_getc() ...... Retrieve incoming character + serial_setbrg() .... Configure port options + serial_init() ...... Initialize the hardware + +The simpliest implementation, supporting only one port, simply defines these six +functions and calls them. Such calls are scattered all around U-Boot, especiall +serial_putc(), serial_puts(), serial_tstc() and serial_getc(). The serial_init() +and serial_setbrg() are often called from platform-dependent places. + +It's important to consider current implementation of CONFIG_SERIAL_MULTI though. +This resides in common/serial.c and behaves as a multiplexer for serial ports. +This, by calling serial_assign(), allows user to switch I/O from one serial port +to another. Though the environmental variables "stdin", "stdout", "stderr" +remain set to "serial". + +These variables are managed by the IOMUX. This resides in common/iomux.c and +manages all console input/output from U-Boot. For serial port, only one IOMUX is +always registered, called "serial" and the switching of different serial ports +is done by code in common/serial.c. + +On a final note, it's important to mention function default_serial_console(), +which is platform specific and reports the default serial console for the +platform, unless proper environment variable overrides this. + +II) Approach +------------ + +Drivers not using CONFIG_SERIAL_MULTI already will have to be converted to +similar approach. The probe() function of a driver will call a function +registering the driver with a STDIO subsystem core, stdio_device_register(). + +The serial_init() function will now be replaced by probe() function of the +driver, the rest of the components of the driver will be converted to standard +STDIO driver calls. See [ UDM-stdio.txt ] for details. + +The serial_setbrg() function depends on global data pointer. This is wrong, +since there is likely to be user willing to configure different baudrate on two +different serial ports. The function will be replaced with STDIO's "conf()" +call, with STDIO_CONFIG_SERIAL_BAUDRATE argument. + +III) Analysis of in-tree drivers +-------------------------------- + + 1) altera_jtag_uart.c + --------------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 2) altera_uart.c + ---------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 3) arm_dcc.c + ------------ + No support for CONFIG_SERIAL_MULTI. Simple conversion possible, unless used + with CONFIG_ARM_DCC_MULTI. Then it registers another separate IOMUX. + + 4) atmel_usart.c + ---------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 5) mcfuart.c + ------------ + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 6) ns16550.c + ------------ + This driver seems complicated and certain consideration will need to be made + during conversion. This driver is implemented in very universal manner, + therefore it'll be necessary to properly design it's platform_data. + + 7) ns9750_serial.c + ------------------ + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 8) opencores_yanu.c + ------------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 9) s3c4510b_uart.c + ------------------ + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 10) s3c64xx.c + ------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 11) sandbox.c + ------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 12) serial.c + ------------ + This is a complementary part of NS16550 UART driver, see above. + + 13) serial_clps7111.c + --------------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 14) serial_imx.c + ---------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. This driver + might be removed in favor of serial_mxc.c . + + 15) serial_ixp.c + ---------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 16) serial_ks8695.c + ------------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 17) serial_lh7a40x.c + -------------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 18) serial_lpc2292.c + -------------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 19) serial_max3100.c + -------------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 20) serial_mxc.c + ---------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 21) serial_netarm.c + ------------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 22) serial_pl01x.c + ------------------ + No support for CONFIG_SERIAL_MULTI. Simple conversion possible, though this + driver in fact contains two drivers in total. + + 23) serial_pxa.c + ---------------- + This driver is a bit complicated, but due to clean support for + CONFIG_SERIAL_MULTI, there are no expected obstructions throughout the + conversion process. + + 24) serial_s3c24x0.c + -------------------- + This driver, being quite ad-hoc might need some work to bring back to shape. + + 25) serial_s3c44b0.c + -------------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 26) serial_s5p.c + ---------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 27) serial_sa1100.c + ------------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 28) serial_sh.c + --------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 29) serial_xuartlite.c + ---------------------- + No support for CONFIG_SERIAL_MULTI. Simple conversion possible. + + 30) usbtty.c + ------------ + This driver seems very complicated and entangled with USB framework. The + conversion might be complicated here. + + 31) arch/powerpc/cpu/mpc512x/serial.c + ------------------------------------- + This driver supports CONFIG_SERIAL_MULTI. This driver will need to be moved to + proper place. |