This adds a serial driver which uses semihosting calls to read and write to the host's console. For convenience, if CONFIG_DM_SERIAL is enabled, we will instantiate a serial driver. This allows users to enable this driver (which has no physical device) without modifying their device trees or board files. We also implement a non-DM driver for SPL, or for much faster output in U-Boot proper.
There are three ways to print to the console:
Method Baud ================== ==== smh_putc in a loop 17 smh_puts 160 smh_write with :tt 2000 ================== ====
These speeds were mesured using a 175 character message with a J-Link adapter. For reference, U-Boot typically prints around 2700 characters during boot on this board. There are two major factors affecting the speed of these functions. First, each breakpoint incurs a delay. Second, each debugger memory transaction incurs a delay. smh_putc has a breakpoint and memory transaction for every character. smh_puts has one breakpoint, but still has to use a transaction for every character. This is because we don't know the length up front, so OpenOCD has to check if each character is nul. smh_write has only one breakpoint and one memory transfer.
DM serial drivers can only implement a putc interface, so we are stuck with the slowest API. Non-DM drivers can implement puts, which is vastly more efficient. When the driver starts up, we try to open :tt. Since this is an extension, this may fail. If it does, we fall back to smh_puts. We don't check :semihosting-features, since there are nonconforming imlementations (OpenOCD) which don't implement it (but *do* implement :tt).
There is no non-blocking I/O available, so we don't implement pending. This will cause __serial_tstc to always return true. If CONFIG_SERIAL_RX_BUFFER is enabled, _serial_tstc will try and read characters forever. To avoid this, we depend on this config being disabled.
Signed-off-by: Sean Anderson sean.anderson@seco.com ---
drivers/serial/Kconfig | 22 ++++++ drivers/serial/Makefile | 1 + drivers/serial/serial.c | 2 + drivers/serial/serial_semihosting.c | 108 ++++++++++++++++++++++++++++ 4 files changed, 133 insertions(+) create mode 100644 drivers/serial/serial_semihosting.c
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig index 345d1881f5..cc20759505 100644 --- a/drivers/serial/Kconfig +++ b/drivers/serial/Kconfig @@ -399,6 +399,15 @@ config DEBUG_UART_SANDBOX start up driver model. The driver will be available until the real driver model serial is running.
+config DEBUG_UART_SEMIHOSTING + bool "semihosting" + depends on SEMIHOSTING_SERIAL + help + Select this to enable the debug UART using the semihosting driver. + This provides basic serial output from the console without needing to + start up driver model. The driver will be available until the real + driver model serial is running. + config DEBUG_UART_SIFIVE bool "SiFive UART" depends on SIFIVE_SERIAL @@ -778,6 +787,19 @@ config SCIF_CONSOLE on systems with RCar or SH SoCs, say Y to this option. If unsure, say N.
+config SEMIHOSTING_SERIAL + bool "Semihosting UART support" + depends on SEMIHOSTING && !SERIAL_RX_BUFFER + help + Select this to enable a serial UART using semihosting. Special halt + instructions will be issued which an external debugger (such as a + JTAG emulator) may interpret. The debugger will display U-Boot's + console output on the host system. + + Enable this option only if you are using a debugger which supports + semihosting. If you are not using a debugger, this driver will halt + the boot. + config UNIPHIER_SERIAL bool "Support for UniPhier on-chip UART" depends on ARCH_UNIPHIER diff --git a/drivers/serial/Makefile b/drivers/serial/Makefile index 52e70aa191..b68b5e7b2b 100644 --- a/drivers/serial/Makefile +++ b/drivers/serial/Makefile @@ -52,6 +52,7 @@ endif obj-$(CONFIG_XILINX_UARTLITE) += serial_xuartlite.o obj-$(CONFIG_SANDBOX_SERIAL) += sandbox.o obj-$(CONFIG_SCIF_CONSOLE) += serial_sh.o +obj-$(CONFIG_SEMIHOSTING_SERIAL) += serial_semihosting.o obj-$(CONFIG_ZYNQ_SERIAL) += serial_zynq.o obj-$(CONFIG_FSL_LPUART) += serial_lpuart.o obj-$(CONFIG_FSL_LINFLEXUART) += serial_linflexuart.o diff --git a/drivers/serial/serial.c b/drivers/serial/serial.c index ebbd21916d..6cdbb89841 100644 --- a/drivers/serial/serial.c +++ b/drivers/serial/serial.c @@ -126,6 +126,7 @@ serial_initfunc(mxc_serial_initialize); serial_initfunc(ns16550_serial_initialize); serial_initfunc(pl01x_serial_initialize); serial_initfunc(pxa_serial_initialize); +serial_initfunc(smh_serial_initialize); serial_initfunc(sh_serial_initialize); serial_initfunc(mtk_serial_initialize);
@@ -180,6 +181,7 @@ int serial_initialize(void) ns16550_serial_initialize(); pl01x_serial_initialize(); pxa_serial_initialize(); + smh_serial_initialize(); sh_serial_initialize(); mtk_serial_initialize();
diff --git a/drivers/serial/serial_semihosting.c b/drivers/serial/serial_semihosting.c new file mode 100644 index 0000000000..44a67c5cb6 --- /dev/null +++ b/drivers/serial/serial_semihosting.c @@ -0,0 +1,108 @@ +// SPDX-License-Identifier: GPL-2.0+ +/* + * Copyright (C) 2022 Sean Anderson sean.anderson@seco.com + */ + +#include <common.h> +#include <dm.h> +#include <serial.h> +#include <semihosting.h> + +#if CONFIG_IS_ENABLED(DM_SERIAL) +static int smh_serial_getc(struct udevice *dev) +{ + return smh_getc(); +} + +static int smh_serial_putc(struct udevice *dev, const char ch) +{ + smh_putc(ch); + return 0; +} + +static const struct dm_serial_ops smh_serial_ops = { + .putc = smh_serial_putc, + .getc = smh_serial_getc, +}; + +U_BOOT_DRIVER(smh_serial) = { + .name = "serial_semihosting", + .id = UCLASS_SERIAL, + .ops = &smh_serial_ops, + .flags = DM_FLAG_PRE_RELOC, +}; + +U_BOOT_DRVINFO(smh_serial) = { + .name = "serial_semihosting", +}; +#else /* DM_SERIAL */ +static int outfd = -ENODEV; + +static int smh_serial_start(void) +{ + outfd = smh_open(":tt", MODE_WRITE); + return 0; +} + +static int smh_serial_stop(void) +{ + if (outfd >= 0) + smh_close(outfd); + return 0; +} + +static void smh_serial_setbrg(void) +{ +} + +static int smh_serial_tstc(void) +{ + return 1; +} + +static void smh_serial_puts(const char *s) +{ + ulong unused; + + if (outfd < 0) + smh_puts(s); + else + smh_write(outfd, s, strlen(s), &unused); +} + +static struct serial_device smh_serial_drv = { + .name = "serial_smh", + .start = smh_serial_start, + .stop = smh_serial_stop, + .setbrg = smh_serial_setbrg, + .getc = smh_getc, + .tstc = smh_serial_tstc, + .putc = smh_putc, + .puts = smh_serial_puts, +}; + +void smh_serial_initialize(void) +{ + serial_register(&smh_serial_drv); +} + +struct serial_device *default_serial_console(void) +{ + return &smh_serial_drv; +} +#endif + +#ifdef CONFIG_DEBUG_UART_SEMIHOSTING +#include <debug_uart.h> + +static inline void _debug_uart_init(void) +{ +} + +static inline void _debug_uart_putc(int c) +{ + smh_putc(c); +} + +DEBUG_UART_FUNCS +#endif