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Message-Id: <20250108004730.2302996-1-fj6611ie@aa.jp.fujitsu.com>
Date: Wed, 8 Jan 2025 00:47:30 +0000
From: Toshiyuki Sato <fj6611ie@...jp.fujitsu.com>
To: Russell King <linux@...linux.org.uk>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jirislaby@...nel.org>
Cc: linux-kernel@...r.kernel.org,
linux-serial@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org,
fj6611ie@...jp.fujitsu.com
Subject: [PATCH] serial: amba-pl011: Implement nbcon console
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);
+
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
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