Add support for the UART provided by the LiteX SoC
framework (https://github.com/enjoy-digital/litex),
based on its FDT info (described in the Linux tree at
Documentation/devicetree/bindings/serial/litex,liteuart.yaml).

Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
---
New in v4:
        - fix typo(s) in commit blurb
        - explicitly disable IRQs during Litex UART initialization

quoted

New in v3:
      - less verbose / more concise commit blurb :)
      - fixed serial_litex_init() alignment
      - fixed `uart_base` pointer arithmetic
      - treat single-bit registers as Boolean
      - removed access to `event` (irq-related) register
        (not needed since UART is operated in polling mode)

quoted

New in v2:
     - remove properties (and parameters) not actually used by the
       LiteX UART
     - remove redundant parentheses from pointer arithmetic
       (thanks jrtc27!)

quoted

See https://github.com/litex-hub/linux-on-litex-rocket for instructions
on how to build a LiteX+Rocket bitstream for e.g. the nexys4ddr (Xilinx
Artix7 FPGA dev board), and https://pastebin.com/nu1dSE16 for a demo of
the board booting a linux payload via opensbi, using this patch.

 include/sbi_utils/fdt/fdt_helper.h    |  3 ++
 include/sbi_utils/serial/litex-uart.h | 17 ++++++++
 lib/utils/fdt/fdt_helper.c            | 19 ++++++++
 lib/utils/serial/fdt_serial.c         |  2 +
 lib/utils/serial/fdt_serial_litex.c   | 35 +++++++++++++++
 lib/utils/serial/litex-uart.c         | 63 +++++++++++++++++++++++++++
 lib/utils/serial/objects.mk           |  2 +
 7 files changed, 141 insertions(+)
 create mode 100644 include/sbi_utils/serial/litex-uart.h
 create mode 100644 lib/utils/serial/fdt_serial_litex.c
 create mode 100644 lib/utils/serial/litex-uart.c

diff --git a/include/sbi_utils/fdt/fdt_helper.h b/include/sbi_utils/fdt/fdt_helper.h
index 24fee7a..5f75f07 100644
--- a/include/sbi_utils/fdt/fdt_helper.h
+++ b/include/sbi_utils/fdt/fdt_helper.h

@@ -62,6 +62,9 @@ int fdt_parse_shakti_uart_node(void *fdt, int nodeoffset,
 int fdt_parse_sifive_uart_node(void *fdt, int nodeoffset,
                               struct platform_uart_data *uart);

+int fdt_parse_litex_uart_node(void *fdt, int nodeoffset,
+                             struct platform_uart_data *uart);
+
 int fdt_parse_uart8250_node(void *fdt, int nodeoffset,
                            struct platform_uart_data *uart);

diff --git a/include/sbi_utils/serial/litex-uart.h b/include/sbi_utils/serial/litex-uart.h
new file mode 100644
index 0000000..91ab644
--- /dev/null
+++ b/include/sbi_utils/serial/litex-uart.h

@@ -0,0 +1,17 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2021 Gabriel Somlo
+ *
+ * Authors:
+ *   Gabriel Somlo <gsomlo@gmail.com>
+ */
+
+#ifndef __SERIAL_LITEX_UART_H__
+#define __SERIAL_LITEX_UART_H__
+
+#include <sbi/sbi_types.h>
+
+int litex_uart_init(unsigned long base);
+
+#endif

diff --git a/lib/utils/fdt/fdt_helper.c b/lib/utils/fdt/fdt_helper.c
index 5bf4021..a42f53b 100644
--- a/lib/utils/fdt/fdt_helper.c
+++ b/lib/utils/fdt/fdt_helper.c

@@ -403,6 +403,25 @@ int fdt_parse_sifive_uart_node(void *fdt, int nodeoffset,
        return 0;
 }

+int fdt_parse_litex_uart_node(void *fdt, int nodeoffset,
+                             struct platform_uart_data *uart)
+{
+       int rc;
+       uint64_t reg_addr, reg_size;
+
+       if (nodeoffset < 0 || !uart || !fdt)
+               return SBI_ENODEV;
+
+       rc = fdt_get_node_addr_size(fdt, nodeoffset, 0, &reg_addr, &reg_size);
+       if (rc < 0 || !reg_addr || !reg_size)
+               return SBI_ENODEV;
+       uart->addr = reg_addr;
+
+       /* LiteX UART has no further configurable properties */
+
+       return 0;
+}
+

 int fdt_parse_uart8250_node(void *fdt, int nodeoffset,
                            struct platform_uart_data *uart)
 {

diff --git a/lib/utils/serial/fdt_serial.c b/lib/utils/serial/fdt_serial.c
index cedda04..f73d26a 100644
--- a/lib/utils/serial/fdt_serial.c
+++ b/lib/utils/serial/fdt_serial.c

@@ -15,6 +15,7 @@

 extern struct fdt_serial fdt_serial_uart8250;
 extern struct fdt_serial fdt_serial_sifive;
+extern struct fdt_serial fdt_serial_litex;
 extern struct fdt_serial fdt_serial_htif;
 extern struct fdt_serial fdt_serial_shakti;
 extern struct fdt_serial fdt_serial_gaisler;

@@ -22,6 +23,7 @@ extern struct fdt_serial fdt_serial_gaisler;
 static struct fdt_serial *serial_drivers[] = {
        &fdt_serial_uart8250,
        &fdt_serial_sifive,
+       &fdt_serial_litex,
        &fdt_serial_htif,
        &fdt_serial_shakti,
        &fdt_serial_gaisler

diff --git a/lib/utils/serial/fdt_serial_litex.c b/lib/utils/serial/fdt_serial_litex.c
new file mode 100644
index 0000000..0fa5777
--- /dev/null
+++ b/lib/utils/serial/fdt_serial_litex.c

@@ -0,0 +1,35 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2021 Gabriel Somlo
+ *
+ * Authors:
+ *   Gabriel Somlo <gsomlo@gmail.com>
+ */
+
+#include <sbi_utils/fdt/fdt_helper.h>
+#include <sbi_utils/serial/fdt_serial.h>
+#include <sbi_utils/serial/litex-uart.h>
+
+static int serial_litex_init(void *fdt, int nodeoff,
+                            const struct fdt_match *match)
+{
+       int rc;
+       struct platform_uart_data uart;
+
+       rc = fdt_parse_litex_uart_node(fdt, nodeoff, &uart);
+       if (rc)
+               return rc;
+
+       return litex_uart_init(uart.addr);
+}
+
+static const struct fdt_match serial_litex_match[] = {
+       { .compatible = "litex,liteuart" },
+       { },
+};
+
+struct fdt_serial fdt_serial_litex = {
+       .match_table = serial_litex_match,
+       .init = serial_litex_init
+};

diff --git a/lib/utils/serial/litex-uart.c b/lib/utils/serial/litex-uart.c
new file mode 100644
index 0000000..f843bf3
--- /dev/null
+++ b/lib/utils/serial/litex-uart.c

@@ -0,0 +1,63 @@
+/*
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2021 Gabriel Somlo
+ *
+ * Authors:
+ *   Gabriel Somlo <gsomlo@gmail.com>
+ */
+
+#include <sbi/riscv_io.h>
+#include <sbi/sbi_console.h>
+#include <sbi_utils/serial/litex-uart.h>
+
+/* clang-format off */
+
+#define UART_REG_RXTX          0
+#define UART_REG_TXFULL                1
+#define UART_REG_RXEMPTY       2
+#define UART_REG_EV_STATUS     3
+#define UART_REG_EV_PENDING    4
+#define UART_REG_EV_ENABLE     5
+
+/* clang-format on */
+
+static volatile u32 *uart_base;
+
+static u8 get_reg(u8 reg)
+{
+       return readb(uart_base + reg);
+}
+
+static void set_reg(u8 reg, u8 val)
+{
+       writeb(val, uart_base + reg);
+}
+
+static void litex_uart_putc(char ch)
+{
+       while (get_reg(UART_REG_TXFULL));
+       set_reg(UART_REG_RXTX, ch);
+}
+
+static int litex_uart_getc(void)
+{
+       if (get_reg(UART_REG_RXEMPTY))
+               return -1;
+       else
+               return get_reg(UART_REG_RXTX);
+}
+
+static struct sbi_console_device litex_console = {
+       .name = "litex_uart",
+       .console_putc = litex_uart_putc,
+       .console_getc = litex_uart_getc
+};
+
+int litex_uart_init(unsigned long base)
+{
+       uart_base = (volatile u32 *)base;
+       set_reg(UART_REG_EV_ENABLE, 0); /* UART in polling mode: disable IRQ */
+       sbi_console_set_device(&litex_console);
+       return 0;
+}

diff --git a/lib/utils/serial/objects.mk b/lib/utils/serial/objects.mk
index 9fb0902..4f751ba 100644
--- a/lib/utils/serial/objects.mk
+++ b/lib/utils/serial/objects.mk

@@ -12,8 +12,10 @@ libsbiutils-objs-y += serial/fdt_serial_gaisler.o
 libsbiutils-objs-y += serial/fdt_serial_htif.o
 libsbiutils-objs-y += serial/fdt_serial_shakti.o
 libsbiutils-objs-y += serial/fdt_serial_sifive.o
+libsbiutils-objs-y += serial/fdt_serial_litex.o
 libsbiutils-objs-y += serial/fdt_serial_uart8250.o
 libsbiutils-objs-y += serial/gaisler-uart.o
 libsbiutils-objs-y += serial/shakti-uart.o
 libsbiutils-objs-y += serial/sifive-uart.o
+libsbiutils-objs-y += serial/litex-uart.o
 libsbiutils-objs-y += serial/uart8250.o
--

2.31.1


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