[PATCH v5] lib: utils: Add LiteX UART support

[Anup Patel]

On Wed, Nov 17, 2021 at 12:47 AM Gabriel Somlo <gsomlo at gmail.com> wrote:
>
> 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 at gmail.com>
> Reviewed-by: Xiang W <wxjstz at 126.com>
> Reviewed-by: Anup Patel <anup.patel at wdc.com>

Applied this patch to the riscv/opensbi repo.

Thanks,
Anup

> ---
> New in v5:
>         - picked up r/b tags from Xiang and Anup
>         - dropped fdt_parse_litex_uart_node(), using
>           fdt_get_node_addr_size() directly from serial_litex_init()
>
> >New in v4:
> >       - fix typo(s) in commit blurb
> >       - explicitly disable IRQs during Litex UART initialization
> >
> >>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)
> >>
> >>> New in v2:
> >>>     - remove properties (and parameters) not actually used by the
> >>>       LiteX UART
> >>>     - remove redundant parentheses from pointer arithmetic
> >>>       (thanks jrtc27!)
> >>>
> >>>> 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/serial/litex-uart.h | 17 ++++++++
>  lib/utils/serial/fdt_serial.c         |  2 +
>  lib/utils/serial/fdt_serial_litex.c   | 39 +++++++++++++++++
>  lib/utils/serial/litex-uart.c         | 63 +++++++++++++++++++++++++++
>  lib/utils/serial/objects.mk           |  2 +
>  5 files changed, 123 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/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 at 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/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..3b3b306
> --- /dev/null
> +++ b/lib/utils/serial/fdt_serial_litex.c
> @@ -0,0 +1,39 @@
> +/*
> + * SPDX-License-Identifier: BSD-2-Clause
> + *
> + * Copyright (c) 2021 Gabriel Somlo
> + *
> + * Authors:
> + *   Gabriel Somlo <gsomlo at gmail.com>
> + */
> +
> +#include <sbi/sbi_error.h>
> +#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)
> +{
> +       uint64_t reg_addr, reg_size;
> +       int rc;
> +
> +       if (nodeoff < 0 || !fdt)
> +               return SBI_ENODEV;
> +
> +       rc = fdt_get_node_addr_size(fdt, nodeoff, 0, &reg_addr, &reg_size);
> +       if (rc < 0 || !reg_addr || !reg_size)
> +               return SBI_ENODEV;
> +
> +       return litex_uart_init(reg_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 at 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
>