Re: [PATCH 3/7] ns8250: Add base support for MMIO UARTs

[Daniel Kiper]

On Fri, Dec 02, 2022 at 10:05:22AM +1100, Benjamin Herrenschmidt wrote:
> From: Benjamin Herrenschmidt <benh@amazon.com>
>
> This adds the ability for the driver to access UARTs via MMIO instead
> of PIO selectively at runtime, and exposes a new function to add an
> MMIO port.
>
> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> ---
>  grub-core/term/ns8250.c | 78 ++++++++++++++++++++++++++++++++---------
>  grub-core/term/serial.c |  8 +++--
>  include/grub/serial.h   | 11 +++++-
>  3 files changed, 78 insertions(+), 19 deletions(-)
>
> diff --git a/grub-core/term/ns8250.c b/grub-core/term/ns8250.c
> index 83b25990c..b640508d0 100644
> --- a/grub-core/term/ns8250.c
> +++ b/grub-core/term/ns8250.c
> @@ -43,6 +43,24 @@ static int dead_ports = 0;
>  #define DEFAULT_BASE_CLOCK 115200
>  #endif
>
> +static inline unsigned char

Please drop inline from here. Then compiler will be free to optimize out
or not this function.

> +ns8250_reg_read (struct grub_serial_port *port, grub_addr_t reg)
> +{
> +  asm volatile("" : : : "memory");
> +  if (port->mmio)
> +    return *((volatile unsigned char *)(port->mmio_base + reg));
> +  return grub_inb (port->port + reg);
> +}
> +
> +static inline void

Ditto...

> +ns8250_reg_write (struct grub_serial_port *port, unsigned char value, 
> grub_addr_t reg)
> +{
> +  asm volatile("" : : : "memory");
> +  if (port->mmio)
> +    *((volatile char *)(port->mmio_base + reg)) = value;

Casts require space like this: (volatile char *) (port->mmio_base + reg).
Please fix casts in other places/patches too.

> +  else
> +    grub_outb (value, port->port + reg);
> +}
>
>  /* Convert speed to divisor.  */
>  static unsigned short
> @@ -93,43 +111,42 @@ do_real_config (struct grub_serial_port *port)
>    divisor = serial_get_divisor (port, &port->config);
>
>    /* Turn off the interrupt.  */
> -  grub_outb (0, port->port + UART_IER);
> +  ns8250_reg_write (port, 0, UART_IER);
>
>    /* Set DLAB.  */
> -  grub_outb (UART_DLAB, port->port + UART_LCR);
> +  ns8250_reg_write (port, UART_DLAB, UART_LCR);
>
> -  /* Set the baud rate.  */
> -  grub_outb (divisor & 0xFF, port->port + UART_DLL);
> -  grub_outb (divisor >> 8, port->port + UART_DLH);
> +  ns8250_reg_write (port, divisor & 0xFF, UART_DLL);
> +  ns8250_reg_write (port, divisor >> 8, UART_DLH);
>
>    /* Set the line status.  */
>    status |= (parities[port->config.parity]
>            | (port->config.word_len - 5)
>            | stop_bits[port->config.stop_bits]);
> -  grub_outb (status, port->port + UART_LCR);
> +  ns8250_reg_write (port, status, UART_LCR);
>
>    if (port->config.rtscts)
>      {
>        /* Enable the FIFO.  */
> -      grub_outb (UART_ENABLE_FIFO_TRIGGER1, port->port + UART_FCR);
> +      ns8250_reg_write (port, UART_ENABLE_FIFO_TRIGGER1, UART_FCR);
>
>        /* Turn on DTR and RTS.  */
> -      grub_outb (UART_ENABLE_DTRRTS, port->port + UART_MCR);
> +      ns8250_reg_write (port, UART_ENABLE_DTRRTS, UART_MCR);
>      }
>    else
>      {
>        /* Enable the FIFO.  */
> -      grub_outb (UART_ENABLE_FIFO_TRIGGER14, port->port + UART_FCR);
> +      ns8250_reg_write (port, UART_ENABLE_FIFO_TRIGGER14, UART_FCR);
>
>        /* Turn on DTR, RTS, and OUT2.  */
> -      grub_outb (UART_ENABLE_DTRRTS | UART_ENABLE_OUT2, port->port + 
> UART_MCR);
> +      ns8250_reg_write (port, UART_ENABLE_DTRRTS | UART_ENABLE_OUT2, 
> UART_MCR);
>      }
>
>    /* Drain the input buffer.  */
>    endtime = grub_get_time_ms () + 1000;
> -  while (grub_inb (port->port + UART_LSR) & UART_DATA_READY)
> +  while (ns8250_reg_read (port, UART_LSR) & UART_DATA_READY)
>      {
> -      grub_inb (port->port + UART_RX);
> +      ns8250_reg_read (port, UART_RX);
>        if (grub_get_time_ms () > endtime)
>       {
>         port->broken = 1;
> @@ -145,8 +162,8 @@ static int
>  serial_hw_fetch (struct grub_serial_port *port)
>  {
>    do_real_config (port);
> -  if (grub_inb (port->port + UART_LSR) & UART_DATA_READY)
> -    return grub_inb (port->port + UART_RX);
> +  if (ns8250_reg_read (port, UART_LSR) & UART_DATA_READY)
> +    return ns8250_reg_read (port, UART_RX);
>
>    return -1;
>  }
> @@ -166,7 +183,7 @@ serial_hw_put (struct grub_serial_port *port, const int c)
>    else
>      endtime = grub_get_time_ms () + 200;
>    /* Wait until the transmitter holding register is empty.  */
> -  while ((grub_inb (port->port + UART_LSR) & UART_EMPTY_TRANSMITTER) == 0)
> +  while ((ns8250_reg_read (port, UART_LSR) & UART_EMPTY_TRANSMITTER) == 0)
>      {
>        if (grub_get_time_ms () > endtime)
>       {
> @@ -179,7 +196,7 @@ serial_hw_put (struct grub_serial_port *port, const int c)
>    if (port->broken)
>      port->broken--;
>
> -  grub_outb (c, port->port + UART_TX);
> +  ns8250_reg_write (port, c, UART_TX);
>  }
>
>  /* Initialize a serial device. PORT is the port number for a serial device.
> @@ -262,6 +279,7 @@ grub_ns8250_init (void)
>       com_ports[i].name = com_names[i];
>       com_ports[i].driver = &grub_ns8250_driver;
>       com_ports[i].port = serial_hw_io_addr[i];
> +     com_ports[i].mmio = 0;
>       err = grub_serial_config_defaults (&com_ports[i]);
>       if (err)
>         grub_print_error ();
> @@ -316,8 +334,36 @@ grub_serial_ns8250_add_port (grub_port_t port)
>      }
>    p->driver = &grub_ns8250_driver;
>    grub_serial_config_defaults (p);
> +  p->mmio = 0;
>    p->port = port;
>    grub_serial_register (p);
>
>    return p->name;
>  }
> +
> +char *
> +grub_serial_ns8250_add_mmio(grub_addr_t addr)
> +{
> +  struct grub_serial_port *p;
> +  unsigned i;

Please add en empty line here.

> +  for (i = 0; i < GRUB_SERIAL_PORT_NUM; i++)
> +    if (com_ports[i].mmio &&  com_ports[i].mmio_base == addr)
> +     return com_names[i];
> +
> +  p = grub_malloc (sizeof (*p));
> +  if (!p)

I prefer "p == NULL" instead of "!p". If you could fix that here and in
the other places/patches that will be nice.

> +    return NULL;
> +  p->name = grub_xasprintf ("mmio,%llx", (unsigned long long) addr);
> +  if (!p->name)
> +    {
> +      grub_free (p);
> +      return NULL;
> +    }
> +  p->driver = &grub_ns8250_driver;
> +  grub_serial_config_defaults (p);
> +  p->mmio = 1;
> +  p->mmio_base = addr;
> +  grub_serial_register (p);
> +
> +  return p->name;
> +}
> diff --git a/grub-core/term/serial.c b/grub-core/term/serial.c
> index 842322b1c..c8f5f02db 100644
> --- a/grub-core/term/serial.c
> +++ b/grub-core/term/serial.c
> @@ -201,8 +201,12 @@ grub_cmd_serial (grub_extcmd_context_t ctxt, int argc, 
> char **args)
>
>    if (state[OPTION_PORT].set)
>      {
> -      grub_snprintf (pname, sizeof (pname), "port%lx",
> -                  grub_strtoul (state[1].arg, 0, 0));
> +      if (grub_memcmp (state[OPTION_PORT].arg, "mmio", 4) == 0)
> +          grub_snprintf(pname, sizeof (pname), "%s", state[1].arg);
> +      else
> +          grub_snprintf (pname, sizeof (pname), "port%lx",
> +                         grub_strtoul (state[1].arg, 0, 0));
> +
>        name = pname;
>      }
>
> diff --git a/include/grub/serial.h b/include/grub/serial.h
> index 67379de45..ccf464d41 100644
> --- a/include/grub/serial.h
> +++ b/include/grub/serial.h
> @@ -86,9 +86,17 @@ struct grub_serial_port
>     */
>    union
>    {
> +    struct
> +    {
> +      int mmio;

Could you use bool here and true/false in the code?

> +      union
> +      {
>  #if defined(__mips__) || defined (__i386__) || defined (__x86_64__)
> -    grub_port_t port;
> +        grub_port_t port;
>  #endif
> +        grub_addr_t mmio_base;
> +      };
> +    };
>      struct
>      {
>        grub_usb_device_t usbdev;
> @@ -178,6 +186,7 @@ grub_serial_config_defaults (struct grub_serial_port 
> *port)
>  #if defined(__mips__) || defined (__i386__) || defined (__x86_64__)
>  void grub_ns8250_init (void);
>  char *grub_serial_ns8250_add_port (grub_port_t port);
> +char *grub_serial_ns8250_add_mmio(grub_addr_t addr);

Please do not drop space before "(". I saw similar mistakes in the other 
patches.

Daniel