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42 lines
1.8 KiB
Text
42 lines
1.8 KiB
Text
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Fetch serial baudrate from DT
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To support fetching of baudrate from DT, the following is done:-
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The baudrate configured in Kconfig symbol CONFIG_BAUDRATE is taken by default by serial.
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If change of baudrate is required then the Kconfig symbol CONFIG_BAUDRATE needs to
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changed and U-Boot recompilation is required or the U-Boot environment needs to be updated.
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To avoid this, add support to fetch the baudrate directly from the device tree file and
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update the environment.
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The default environment stores the default baudrate value. When default baudrate and dtb
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baudrate are not same glitches are seen on the serial.
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So, the environment also needs to be updated with the dtb baudrate to avoid the glitches on
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the serial which is enabled by OF_SERIAL_BAUD.
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The Kconfig SPL_ENV_SUPPORT needs to be enabled to allow patching in SPL.
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The Kconfig DEFAULT_ENV_IS_RW which is enabled by OF_SERIAL_BAUD with making the environment
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writable.
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The ofnode_read_baud() function parses and fetches the baudrate value from the DT. This value
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is validated and updated to baudrate during serial init. Padding is added at the end of the
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default environment and the dt baudrate is updated with the latest value.
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Example:-
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The serial port options are of the form "bbbbpnf", where "bbbb" is the baud rate, "p" is parity ("n", "o", or "e"),
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"n" is number of bits, and "f" is flow control ("r" for RTS or omit it). Default is "115200n8".
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chosen {
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bootargs = "earlycon console=ttyPS0,115200 clk_ignore_unused root=/dev/ram0 rw init_fatal_sh=1";
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stdout-path = "serial0:115200n8";
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};
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From the chosen node, stdout-path property is obtained as string.
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stdout-path = "serial0:115200n8";
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The string is parsed to get the baudrate 115200. This string is converted to integer and updated to the environment.
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