mirror of
https://github.com/AsahiLinux/u-boot
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b9f4bc34ac
Since commit 957731ed (ARM: remove broken "lpd7a40x" boards),
lh7a40x cpu and serial driver have become unused. Remove them.
Signed-off-by: Albert ARIBAUD <albert.u.boot@aribaud.net>
187 lines
6.2 KiB
Text
187 lines
6.2 KiB
Text
The U-Boot Driver Model Project
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===============================
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Serial I/O 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 serial port support currently requires the driver to export the following
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functions:
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serial_putc() ...... Output a character
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serial_puts() ...... Output string, often done using serial_putc()
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serial_tstc() ...... Test if incoming character is in a buffer
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serial_getc() ...... Retrieve incoming character
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serial_setbrg() .... Configure port options
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serial_init() ...... Initialize the hardware
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The simpliest implementation, supporting only one port, simply defines these six
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functions and calls them. Such calls are scattered all around U-Boot, especiall
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serial_putc(), serial_puts(), serial_tstc() and serial_getc(). The serial_init()
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and serial_setbrg() are often called from platform-dependent places.
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It's important to consider current implementation of CONFIG_SERIAL_MULTI though.
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This resides in common/serial.c and behaves as a multiplexer for serial ports.
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This, by calling serial_assign(), allows user to switch I/O from one serial port
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to another. Though the environmental variables "stdin", "stdout", "stderr"
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remain set to "serial".
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These variables are managed by the IOMUX. This resides in common/iomux.c and
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manages all console input/output from U-Boot. For serial port, only one IOMUX is
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always registered, called "serial" and the switching of different serial ports
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is done by code in common/serial.c.
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On a final note, it's important to mention function default_serial_console(),
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which is platform specific and reports the default serial console for the
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platform, unless proper environment variable overrides this.
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II) Approach
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------------
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Drivers not using CONFIG_SERIAL_MULTI already will have to be converted to
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similar approach. The probe() function of a driver will call a function
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registering the driver with a STDIO subsystem core, stdio_device_register().
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The serial_init() function will now be replaced by probe() function of the
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driver, the rest of the components of the driver will be converted to standard
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STDIO driver calls. See [ UDM-stdio.txt ] for details.
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The serial_setbrg() function depends on global data pointer. This is wrong,
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since there is likely to be user willing to configure different baudrate on two
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different serial ports. The function will be replaced with STDIO's "conf()"
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call, with STDIO_CONFIG_SERIAL_BAUDRATE argument.
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III) Analysis of in-tree drivers
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--------------------------------
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1) altera_jtag_uart.c
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---------------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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2) altera_uart.c
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----------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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3) arm_dcc.c
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------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible, unless used
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with CONFIG_ARM_DCC_MULTI. Then it registers another separate IOMUX.
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4) atmel_usart.c
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----------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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5) mcfuart.c
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------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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6) ns16550.c
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------------
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This driver seems complicated and certain consideration will need to be made
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during conversion. This driver is implemented in very universal manner,
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therefore it'll be necessary to properly design it's platform_data.
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7) ns9750_serial.c
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------------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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8) opencores_yanu.c
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-------------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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9) s3c4510b_uart.c
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------------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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10) s3c64xx.c
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-------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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11) sandbox.c
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-------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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12) serial.c
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------------
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This is a complementary part of NS16550 UART driver, see above.
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13) serial_clps7111.c
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---------------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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14) serial_imx.c
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----------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible. This driver
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might be removed in favor of serial_mxc.c .
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15) serial_ixp.c
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----------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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16) serial_ks8695.c
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-------------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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17) serial_lpc2292.c
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--------------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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18) serial_max3100.c
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--------------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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19) serial_mxc.c
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----------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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20) serial_netarm.c
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-------------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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21) serial_pl01x.c
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------------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible, though this
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driver in fact contains two drivers in total.
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22) serial_pxa.c
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----------------
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This driver is a bit complicated, but due to clean support for
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CONFIG_SERIAL_MULTI, there are no expected obstructions throughout the
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conversion process.
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23) serial_s3c24x0.c
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--------------------
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This driver, being quite ad-hoc might need some work to bring back to shape.
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24) serial_s3c44b0.c
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--------------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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25) serial_s5p.c
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----------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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26) serial_sa1100.c
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-------------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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27) serial_sh.c
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---------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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28) serial_xuartlite.c
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----------------------
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No support for CONFIG_SERIAL_MULTI. Simple conversion possible.
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29) usbtty.c
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------------
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This driver seems very complicated and entangled with USB framework. The
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conversion might be complicated here.
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30) arch/powerpc/cpu/mpc512x/serial.c
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-------------------------------------
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This driver supports CONFIG_SERIAL_MULTI. This driver will need to be moved to
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proper place.
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