Re: [PATCH v3 16/29] serial: Add semihosting driver

Hi Sean,

On Tue, 22 Mar 2022 at 15:00, Sean Anderson sean.anderson@seco.com wrote:

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 170 smh_puts 1600 smh_write with :tt 20000 ================== =====

These speeds were measured 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 implementations (OpenOCD) which don't implement it (but *do* implement :tt).

Some semihosting implementations (QEMU) don't handle READC properly. To work around this, we try to use open/read (much like for stdin) if possible.

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

(no changes since v2)

Changes in v2:

• Fix baud numbers being off by 10
• Fix typos in commit message
• Rename non-DM driver struct to match format of other drivers

drivers/serial/Kconfig | 22 +++++ drivers/serial/Makefile | 1 + drivers/serial/serial.c | 2 + drivers/serial/serial_semihosting.c | 147 ++++++++++++++++++++++++++++ include/serial.h | 1 + 5 files changed, 173 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..7c7c5d9455 --- /dev/null +++ b/drivers/serial/serial_semihosting.c @@ -0,0 +1,147 @@ +// 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>

+/**

• • struct smh_serial_priv - Semihosting serial private data
• • @infd: stdin file descriptor (or error)
• */

+struct smh_serial_priv {

•   int infd;
  

•   int outfd;
  

+};

+#if CONFIG_IS_ENABLED(DM_SERIAL) +static int smh_serial_getc(struct udevice *dev) +{

•   char ch = 0;
  

•   struct smh_serial_priv *priv = dev_get_priv(dev);
  

•   if (priv->infd < 0)
  

•           return smh_getc();
  

•   smh_read(priv->infd, &ch, sizeof(ch));
  

•   return ch;
  

+}

+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,
  

+};

+static int smh_serial_probe(struct udevice *dev) +{

•   struct smh_serial_priv *priv = dev_get_priv(dev);
  

•   priv->infd = smh_open(":tt", MODE_READ);
  

•   return 0;
  

+}

+U_BOOT_DRIVER(smh_serial) = {

•   .name   = "serial_semihosting",
  

•   .id     = UCLASS_SERIAL,
  

•   .probe  = smh_serial_probe,
  

•   .priv_auto = sizeof(struct smh_serial_priv),
  

•   .ops    = &smh_serial_ops,
  

•   .flags  = DM_FLAG_PRE_RELOC,
  

+};

+U_BOOT_DRVINFO(smh_serial) = {

•   .name = "serial_semihosting",
  

+}; +#else /* DM_SERIAL */ +static int infd = -ENODEV; +static int outfd = -ENODEV;

+static int smh_serial_start(void) +{

•   infd = smh_open(":tt", MODE_READ);
  

•   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_getc(void) +{

•   char ch = 0;
  

•   if (infd < 0)
  

•           return smh_getc();
  

•   smh_read(infd, &ch, sizeof(ch));
  

•   return ch;
  

+}

+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);
  

+}

+struct serial_device serial_smh_device = {

•   .name   = "serial_smh",
  

•   .start  = smh_serial_start,
  

•   .stop   = smh_serial_stop,
  

•   .setbrg = smh_serial_setbrg,
  

•   .getc   = smh_serial_getc,
  

•   .tstc   = smh_serial_tstc,
  

•   .putc   = smh_putc,
  

•   .puts   = smh_serial_puts,
  

+};

+void smh_serial_initialize(void) +{

•   serial_register(&serial_smh_device);
  

+}

+__weak struct serial_device *default_serial_console(void) +{

•   return &serial_smh_device;
  

+} +#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 diff --git a/include/serial.h b/include/serial.h index 19a8c0c67d..2681d26c82 100644 --- a/include/serial.h +++ b/include/serial.h @@ -23,6 +23,7 @@ struct serial_device { void default_serial_puts(const char *s);

extern struct serial_device serial_smc_device; +extern struct serial_device serial_smh_device; extern struct serial_device serial_scc_device; extern struct serial_device *default_serial_console(void);

-- 2.25.1