Re: [PATCH v2] serial: Poll USB devices if usbX serial port is missing

[Andrei Borzenkov <arvidjaar@gmail.com>]

On Fri, Nov 18, 2016 at 1:36 PM, Joonas Lahtinen
<joonas.lahtinen@linux.intel.com> wrote:
> If usbX serial port is missing, try to poll USB devices. This makes them
> appear at least on Intel NUC devices DN2820FYKH and DCCP847DYE.
>
> This fixes cases where you try to configure usbX serial at the beginning
> of a script, like:
>
>   serial usb0 --speed=115200 --word=8 --parity=none --stop=1
>   terminal_output --append serial_usb0
>   terminal_input --append serial_usb0
>
> Without this patch the above would fail with:
>
>   serial port `usb0' isn't found
>
> Strangely, adding 'usb' command before the serial initialization
> made it work, and even moving the terminal_output and input command
> to be before. This is due to the terminal_output command detecting
> "serial_usb" and running USB polling if the output is missing. 'usb'
> command from usbtest module always polls USB devices.
>
 As it is the logical thing to configure the serial port before adding
> it as an output or input, this patch makes things works as expected.
> Most online resources mentioning GRUB and USB serial adapters also do
> mention the above order, so there must be quite many struggling with
> this problem on platforms where USB needs to be polled in order for
> the detection to happen.
>
> v2:
> - Use grub_term_poll_usb to avoid module dependency (Andrei)
>

Hmm ... note that terminal_input/terminal_output also auto-load
modules that handle serial ports. So this still will not be
equivalent, it will require user to manually pre-load USB. Did you
actually test this version of patch? Do you pre-load USB modules
somewhere?

The problem is, infrastructure to handle auto-load lists currently
belongs to normal mode, while serial may sensibly be used before
normal is loaded. Not sure what we can do here.

> Cc: Andrei Borzenkov <arvidjaar@gmail.com>
> Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> ---
>  grub-core/term/serial.c | 22 +++++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
>
> diff --git a/grub-core/term/serial.c b/grub-core/term/serial.c
> index db80b3b..1a009a9 100644
> --- a/grub-core/term/serial.c
> +++ b/grub-core/term/serial.c
> @@ -191,6 +191,7 @@ grub_cmd_serial (grub_extcmd_context_t ctxt, int argc, char **args)
>    struct grub_serial_port *port;
>    struct grub_serial_config config;
>    grub_err_t err;
> +  int again;
>
>    if (state[OPTION_UNIT].set)
>      {
> @@ -212,7 +213,26 @@ grub_cmd_serial (grub_extcmd_context_t ctxt, int argc, char **args)
>    if (!name)
>      name = "com0";
>
> -  port = grub_serial_find (name);
> +  again = 0;
> +  while(1)
> +    {
> +      port = grub_serial_find (name);
> +
> +      if (port || again)
> +       break;
> +
> +      if (grub_memcmp (name, "usb", sizeof ("usb") - 1) == 0
> +          && grub_term_poll_usb)
> +       {
> +         grub_term_poll_usb (1);
> +         again = 1;
> +       }
> +      else
> +       {
> +         break;
> +       }
> +    }
> +
>    if (!port)
>      return grub_error (GRUB_ERR_BAD_ARGUMENT,
>                        N_("serial port `%s' isn't found"),
> --
> 2.7.4
>