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[riscv] Write SBI console output to early UART, if enabled

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The early UART is an optional feature used to obtain debug output from
the prefix before iPXE is able to parse the device tree.

Extend this feature to also cover any console output that iPXE
attempts to send to the SBI console, on the basis that the purpose of
the early UART is to provide an output-only device for situations in
which there is no functional SBI console.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2025-06-12 12:57:26 +01:00
parent 41e65df19d
commit 5783a10f72
2 changed files with 31 additions and 0 deletions
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26
src/arch/riscv/prefix/libprefix.S
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@@ -243,6 +243,32 @@ early_uart_sifive_wait_\@:
bltz a1, early_uart_sifive_wait_\@
.endm
/*****************************************************************************
*
* Print single character to early UART (from C code)
*
*****************************************************************************
*
* This function is called by the SBI console driver to output a
* character to the early UART (if enabled).
*
* The standard C ABI applies to this function.
*
* Parameters:
*
* a0 - Character to print
*
* Returns: none
*
*/
.section ".prefix.early_uart_putchar", "ax", @progbits
.globl early_uart_putchar
early_uart_putchar:
print_char_uart
ret
.size early_uart_putchar, . - early_uart_putchar
/*****************************************************************************
*
* Print message to debug console