Implement the callbacks required for an NBCON console [0] on the amba-pl011 console driver. The codes for legacy console are retained, and the module parameter (use_nbcon) allows switching between legacy and NBCON. The default is off (use legacy console) for now. Referred to the NBCON implementation work for 8250 [1] and imx [2]. The normal-priority write_thread checks for console ownership each time a character is printed. write_atomic holds the console ownership until the entire string is printed. UART register operations are protected from other contexts by uart_port_lock, except for a final flush(nbcon_atomic_flush_unsafe) on panic. The patch has been verified to correctly handle the output and competition of messages with different priorities and flushing panic message to console after nmi panic using ARM64 QEMU and a physical machine(A64FX). [0] https://lore.kernel.org/all/ZuRRTbapH0DCj334@xxxxxxxxxxxxxxx/ [1] https://lore.kernel.org/all/20240913140538.221708-1-john.ogness@xxxxxxxxxxxxx/T/ [2] https://lore.kernel.org/linux-arm-kernel/20240913-serial-imx-nbcon-v3-1-4c627302335b@xxxxxxxxxx/T/ Signed-off-by: Toshiyuki Sato <fj6611ie@xxxxxxxxxxxxxxxxx> --- drivers/tty/serial/amba-pl011.c | 113 ++++++++++++++++++++++++++++++++ 1 file changed, 113 insertions(+) diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c index 69b7a3e1e..52fab3170 100644 --- a/drivers/tty/serial/amba-pl011.c +++ b/drivers/tty/serial/amba-pl011.c @@ -41,6 +41,7 @@ #include <linux/sizes.h> #include <linux/io.h> #include <linux/acpi.h> +#include <linux/moduleparam.h> #define UART_NR 14 @@ -263,6 +264,7 @@ struct uart_amba_port { char type[12]; bool rs485_tx_started; unsigned int rs485_tx_drain_interval; /* usecs */ + bool console_line_ended; #ifdef CONFIG_DMA_ENGINE /* DMA stuff */ unsigned int dmacr; /* dma control reg */ @@ -274,6 +276,10 @@ struct uart_amba_port { #endif }; +/* if non-zero, the console is nbcon. */ +static int use_nbcon; +module_param(use_nbcon, int, 0444); + static unsigned int pl011_tx_empty(struct uart_port *port); static unsigned int pl011_reg_to_offset(const struct uart_amba_port *uap, @@ -2305,6 +2311,7 @@ static void pl011_console_putchar(struct uart_port *port, unsigned char ch) while (pl011_read(uap, REG_FR) & UART01x_FR_TXFF) cpu_relax(); pl011_write(ch, uap, REG_DR); + uap->console_line_ended = (ch == '\n'); } static void @@ -2411,6 +2418,8 @@ static int pl011_console_setup(struct console *co, char *options) if (ret) return ret; + uap->console_line_ended = true; + if (dev_get_platdata(uap->port.dev)) { struct amba_pl011_data *plat; @@ -2494,6 +2503,106 @@ static int pl011_console_match(struct console *co, char *name, int idx, return -ENODEV; } +static void +pl011_console_write_atomic(struct console *co, struct nbcon_write_context *wctxt) +{ + struct uart_amba_port *uap = amba_ports[co->index]; + unsigned int old_cr = 0; + + if (!nbcon_enter_unsafe(wctxt)) + return; + + clk_enable(uap->clk); + + if (!uap->vendor->always_enabled) { + old_cr = pl011_read(uap, REG_CR); + pl011_write((old_cr & ~UART011_CR_CTSEN) | (UART01x_CR_UARTEN | UART011_CR_TXE), + uap, REG_CR); + } + + if (!uap->console_line_ended) + uart_console_write(&uap->port, "\n", 1, pl011_console_putchar); + uart_console_write(&uap->port, wctxt->outbuf, wctxt->len, pl011_console_putchar); + + while ((pl011_read(uap, REG_FR) ^ uap->vendor->inv_fr) & uap->vendor->fr_busy) + cpu_relax(); + + if (!uap->vendor->always_enabled) + pl011_write(old_cr, uap, REG_CR); + + clk_disable(uap->clk); + + nbcon_exit_unsafe(wctxt); +} + +static void +pl011_console_write_thread(struct console *co, struct nbcon_write_context *wctxt) +{ + struct uart_amba_port *uap = amba_ports[co->index]; + unsigned int old_cr = 0; + + if (!nbcon_enter_unsafe(wctxt)) + return; + + clk_enable(uap->clk); + + if (!uap->vendor->always_enabled) { + old_cr = pl011_read(uap, REG_CR); + pl011_write((old_cr & ~UART011_CR_CTSEN) | (UART01x_CR_UARTEN | UART011_CR_TXE), + uap, REG_CR); + } + + if (nbcon_exit_unsafe(wctxt)) { + int i; + unsigned int len = READ_ONCE(wctxt->len); + + for (i = 0; i < len; i++) { + if (!nbcon_enter_unsafe(wctxt)) + break; + uart_console_write(&uap->port, wctxt->outbuf + i, 1, pl011_console_putchar); + if (!nbcon_exit_unsafe(wctxt)) + break; + } + } + + while (!nbcon_enter_unsafe(wctxt)) + nbcon_reacquire_nobuf(wctxt); + + while ((pl011_read(uap, REG_FR) ^ uap->vendor->inv_fr) & uap->vendor->fr_busy) + cpu_relax(); + + if (!uap->vendor->always_enabled) + pl011_write(old_cr, uap, REG_CR); + + clk_disable(uap->clk); + + nbcon_exit_unsafe(wctxt); +} + +static void +pl011_console_device_lock(struct console *co, unsigned long *flags) +{ + __uart_port_lock_irqsave(&amba_ports[co->index]->port, flags); +} + +static void +pl011_console_device_unlock(struct console *co, unsigned long flags) +{ + __uart_port_unlock_irqrestore(&amba_ports[co->index]->port, flags); +} + +static void +pl011_console_switch_to_nbcon(struct console *co) +{ + co->write = NULL; + co->write_atomic = pl011_console_write_atomic; + co->write_thread = pl011_console_write_thread; + co->device_lock = pl011_console_device_lock; + co->device_unlock = pl011_console_device_unlock; + co->flags = CON_PRINTBUFFER | CON_ANYTIME | CON_NBCON; + pr_info("Serial: switched to nbcon\n"); +} + static struct uart_driver amba_reg; static struct console amba_console = { .name = "ttyAMA", @@ -2737,6 +2846,10 @@ static int pl011_register_port(struct uart_amba_port *uap) pl011_write(0xffff, uap, REG_ICR); if (!amba_reg.state) { + /* Replaces the console descriptor if NBCON is selected. */ + if (amba_reg.cons && use_nbcon) + pl011_console_switch_to_nbcon(amba_reg.cons); + ret = uart_register_driver(&amba_reg); if (ret < 0) { dev_err(uap->port.dev, -- 2.34.1
