Add an earlycon driver for platforms with TCU, namely Tegra194.
The driver is compatible with boot parameters passed by NVIDIA
boot chains.
Signed-off-by: Mikko Perttunen <mperttunen@xxxxxxxxxx>
---
drivers/tty/serial/Kconfig | 12 +++++
drivers/tty/serial/Makefile | 1 +
drivers/tty/serial/tegra-tcu-earlycon.c | 72 +++++++++++++++++++++++++
3 files changed, 85 insertions(+)
create mode 100644 drivers/tty/serial/tegra-tcu-earlycon.c
diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
index 34a2899e69c0..d941785e3f46 100644
--- a/drivers/tty/serial/Kconfig
+++ b/drivers/tty/serial/Kconfig
@@ -331,6 +331,18 @@ config SERIAL_TEGRA_TCU_CONSOLE
If unsure, say Y.
+config SERIAL_TEGRA_TCU_EARLYCON
+ bool "Earlycon on NVIDIA Tegra Combined UART"
+ depends on ARCH_TEGRA || COMPILE_TEST
+ select SERIAL_EARLYCON
+ select SERIAL_CORE_CONSOLE
+ default y if SERIAL_TEGRA_TCU_CONSOLE
+ help
+ If you say Y here, TCU output will be supported during the earlycon
+ phase of the boot.
+
+ If unsure, say Y.
+
config SERIAL_MAX3100
tristate "MAX3100 support"
depends on SPI
diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
index b85d53f9e9ff..408144326fed 100644
--- a/drivers/tty/serial/Makefile
+++ b/drivers/tty/serial/Makefile
@@ -72,6 +72,7 @@ obj-$(CONFIG_SERIAL_XILINX_PS_UART) += xilinx_uartps.o
obj-$(CONFIG_SERIAL_SIRFSOC) += sirfsoc_uart.o
obj-$(CONFIG_SERIAL_TEGRA) += serial-tegra.o
obj-$(CONFIG_SERIAL_TEGRA_TCU) += tegra-tcu.o
+obj-$(CONFIG_SERIAL_TEGRA_TCU_EARLYCON) += tegra-tcu-earlycon.o
obj-$(CONFIG_SERIAL_AR933X) += ar933x_uart.o
obj-$(CONFIG_SERIAL_EFM32_UART) += efm32-uart.o
obj-$(CONFIG_SERIAL_ARC) += arc_uart.o
diff --git a/drivers/tty/serial/tegra-tcu-earlycon.c b/drivers/tty/serial/tegra-tcu-earlycon.c
new file mode 100644
index 000000000000..9decfbced0a7
--- /dev/null
+++ b/drivers/tty/serial/tegra-tcu-earlycon.c
@@ -0,0 +1,72 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2017-2021, NVIDIA CORPORATION. All rights reserved.
+ */
+
+#include <linux/console.h>
+#include <linux/io.h>
+#include <linux/serial_core.h>
+
+#define NUM_BYTES_FIELD_BIT 24
+#define FLUSH_BIT 26
+#define INTR_TRIGGER_BIT 31
+
+static u32 update_and_send_mbox(u8 __iomem *addr, u32 mbox_val, char c)
+{
+ int bytes = bytes = (mbox_val >> NUM_BYTES_FIELD_BIT) & 0x3;
+
+ mbox_val |= BIT(INTR_TRIGGER_BIT);
+ mbox_val |= c << (bytes * 8);
+ bytes++;
+ mbox_val = (mbox_val & ~(3 << NUM_BYTES_FIELD_BIT)) |
+ (bytes << NUM_BYTES_FIELD_BIT);
+
+ if (bytes == 3) {
+ /* Send current packet to SPE */
+ while (readl(addr) & BIT(INTR_TRIGGER_BIT))
+ cpu_relax();
+ writel(mbox_val, addr);
+ mbox_val = BIT(INTR_TRIGGER_BIT);
+ }
+
+ return mbox_val;
+}
+
+/*
+ * This function splits the string to be printed (const char *s) into multiple
+ * packets. Each packet contains a max of 3 characters. Packets are sent to the
+ * SPE-based combined UART server for printing. Communication with SPE is done
+ * through mailbox registers which can generate interrupts for SPE.
+ */
+static void early_tcu_write(struct console *console, const char *s, unsigned int count)
+{
+ struct earlycon_device *device = console->data;
+ u8 __iomem *addr = device->port.membase;
+ u32 mbox_val = BIT(INTR_TRIGGER_BIT);
+ unsigned int i;
+
+ /* Loop for processing each 3 char packet */
+ for (i = 0; i < count; i++) {
+ if (s[i] == '\n')
+ mbox_val = update_and_send_mbox(addr, mbox_val, '\r');
+ mbox_val = update_and_send_mbox(addr, mbox_val, s[i]);
+ }
+
+ if ((mbox_val >> NUM_BYTES_FIELD_BIT) & 0x3) {
+ while (readl(addr) & BIT(INTR_TRIGGER_BIT))
+ cpu_relax();
+ writel(mbox_val, addr);
+ }
+}
+
+int __init early_tegra_combined_uart_setup(struct earlycon_device *device, const char *options)
+{
+ if (!(device->port.membase))
+ return -ENODEV;
+
+ device->con->write = early_tcu_write;
+
+ return 0;
+}
+
+EARLYCON_DECLARE(tegra_comb_uart, early_tegra_combined_uart_setup);
--
2.30.0
