Hi,
On Tue, Apr 28, 2020 at 9:22 AM Daniel Thompson
<daniel.thompson@xxxxxxxxxx> wrote:
>
> Currently if the kernel has support for ACPI SPCR parsing then earlycon
> without arguments is processed later than the full earlycon=...
> alternative.
>
> If ACPI has been explicitly disabled on the kernel command line then
> there is not need to defer since the ACPI code (both x86 and arm64)
> will never actually run.
>
> Or, put another way it allows lazy people to throw "acpi=off earlycon"
> onto the command line of a DT systems and be confident the console will
> start as early as possible without them having to lookup the driver
> and address needed for a specific platform.
>
> Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> ---
> drivers/tty/serial/earlycon.c | 28 +++++++++++++++++++++++++++-
> 1 file changed, 27 insertions(+), 1 deletion(-)
I wonder if a cleaner option is to just add a special "earlycon" value
like "earlycon=not_acpi". This wouldn't require any special peeking
and would just be a sentinel that just says "you should autodetect the
earlycon, but don't worry about waiting for ACPI". ...that in itself
is a bit of a hack, but at least it's more self contained in the
earlycon driver and maybe more discoverable when someone is figuring
out how to setup earlycon?
-Doug
>
> diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
> index 2ae9190b64bb..ebb648aacb47 100644
> --- a/drivers/tty/serial/earlycon.c
> +++ b/drivers/tty/serial/earlycon.c
> @@ -215,6 +215,31 @@ int __init setup_earlycon(char *buf)
> */
> bool earlycon_acpi_spcr_enable __initdata;
>
> +/*
> + * This takes a sneaky peek at other boot arguments (which may not have
> + * been parsed at this point in the boot) to check whether ACPI has
> + * been explicitly disabled. If it is explicitly disabled then there is
> + * no reason to defer initialization of the early console.
> + */
> +static bool earlycon_check_for_acpi_off(void)
> +{
> + static const char token[] = "acpi=off";
> + const char *arg;
> + char before, after;
> +
> + arg = strstr(boot_command_line, token);
> + while (arg) {
> + before = arg == boot_command_line ? ' ' : arg[-1];
> + after = arg[sizeof(token)-1];
> + if (isspace(before) && (isspace(after) || after == '\0'))
> + return true;
> +
> + arg = strstr(arg+1, token);
> + }
> +
> + return false;
> +}
> +
> /* early_param wrapper for setup_earlycon() */
> static int __init param_setup_earlycon(char *buf)
> {
> @@ -222,7 +247,8 @@ static int __init param_setup_earlycon(char *buf)
>
> /* Just 'earlycon' is a valid param for devicetree and ACPI SPCR. */
> if (!buf || !buf[0]) {
> - if (IS_ENABLED(CONFIG_ACPI_SPCR_TABLE)) {
> + if (IS_ENABLED(CONFIG_ACPI_SPCR_TABLE) &&
> + !earlycon_check_for_acpi_off()) {
> earlycon_acpi_spcr_enable = true;
> return 0;
> } else if (!buf) {
> --
> 2.25.1
>
