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Message-ID: <2025010845-deceiver-imaginary-ea04@gregkh>
Date: Wed, 8 Jan 2025 09:13:12 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Toshiyuki Sato <fj6611ie@...jp.fujitsu.com>
Cc: Russell King <linux@...linux.org.uk>, Jiri Slaby <jirislaby@...nel.org>,
linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] serial: amba-pl011: Implement nbcon console
On Wed, Jan 08, 2025 at 12:47:30AM +0000, Toshiyuki Sato wrote:
> 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@pathway.suse.cz/
> [1] https://lore.kernel.org/all/20240913140538.221708-1-john.ogness@linutronix.de/T/
> [2] https://lore.kernel.org/linux-arm-kernel/20240913-serial-imx-nbcon-v3-1-4c627302335b@geanix.com/T/
>
> Signed-off-by: Toshiyuki Sato <fj6611ie@...jp.fujitsu.com>
> ---
> 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);
Why is a module parameter needed here? That feels wrong and not
scalable at all. What happens if you have multiple devices, which one
is nbcon and which isn't?
> +
> 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");
dev_info()?
thanks,
greg k-h
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