linux-kernel - Re: [PATCH 3/3] ACPI: SPCR: Add support for rev 3

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Message-ID: <CAJZ5v0hmf55OA1f4egzE7F0ET+7af_+pcxmnOSxO5Snd6L5CrQ@mail.gmail.com>
Date: Wed, 2 Oct 2024 20:13:02 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Raul E Rangel <rrangel@...omium.org>
Cc: linux-serial@...r.kernel.org, pmladek@...e.com, rafael.j.wysocki@...el.com, 
	ribalda@...omium.org, Len Brown <lenb@...nel.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Robert Moore <robert.moore@...el.com>, acpica-devel@...ts.linux.dev, 
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] ACPI: SPCR: Add support for rev 3

On Thu, Sep 12, 2024 at 7:39 PM Raul E Rangel <rrangel@...omium.org> wrote:
>
> Revision 3 supports specifying the UART input clock. This allows for
> proper computation of the UART divisor when the baud rate is specified.
>
> The earlycon code can accept the following format (See `parse_options`
> in `earlycon.c`.):
> * <name>,io|mmio|mmio32|mmio32be,<addr>,<baud>,<uartclk>,<options>
>
> This change makes it so the uartclk is passed along if it's defined in
> the SPCR table.
>
> Booting with `earlycon` and a SPCR v3 table that has the uartclk and
> baud defined:
> [    0.028251] ACPI: SPCR: console: uart,mmio32,0xfedc9000,115200,48000000
> [    0.028267] earlycon: uart0 at MMIO32 0x00000000fedc9000 (options '115200,48000000')
> [    0.028272] printk: legacy bootconsole [uart0] enabled
>
> Link: https://learn.microsoft.com/en-us/windows-hardware/drivers/serports/serial-port-console-redirection-table
>
> Signed-off-by: Raul E Rangel <rrangel@...omium.org>
>
> ---
>
>  drivers/acpi/spcr.c   | 5 ++++-
>  include/acpi/actbl3.h | 6 +++---
>  2 files changed, 7 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/acpi/spcr.c b/drivers/acpi/spcr.c
> index cd36a97b0ea2c7..67ae42afcc59ef 100644
> --- a/drivers/acpi/spcr.c
> +++ b/drivers/acpi/spcr.c
> @@ -209,9 +209,12 @@ int __init acpi_parse_spcr(bool enable_earlycon, bool enable_console)
>         if (!baud_rate) {
>                 snprintf(opts, sizeof(opts), "%s,%s,0x%llx", uart, iotype,
>                          table->serial_port.address);
> -       } else {
> +       } else if (table->header.revision <= 2 || !table->uartclk) {
>                 snprintf(opts, sizeof(opts), "%s,%s,0x%llx,%d", uart, iotype,
>                          table->serial_port.address, baud_rate);
> +       } else {
> +               snprintf(opts, sizeof(opts), "%s,%s,0x%llx,%d,%d", uart, iotype,
> +                        table->serial_port.address, baud_rate, table->uartclk);
>         }
>
>         pr_info("console: %s\n", opts);
> diff --git a/include/acpi/actbl3.h b/include/acpi/actbl3.h
> index 8f775e3a08fdfb..afe45a2379866a 100644
> --- a/include/acpi/actbl3.h
> +++ b/include/acpi/actbl3.h

The part of the patch below is outdated - SPCR v4 is supported already.

Please rebase on the current mainline kernel source.

> @@ -92,10 +92,10 @@ struct acpi_table_slit {
>  /*******************************************************************************
>   *
>   * SPCR - Serial Port Console Redirection table
> - *        Version 2
> + *        Version 3
>   *
>   * Conforms to "Serial Port Console Redirection Table",
> - * Version 1.03, August 10, 2015
> + * Version 1.08, October 7, 2021
>   *
>   ******************************************************************************/
>
> @@ -120,7 +120,7 @@ struct acpi_table_spcr {
>         u8 pci_function;
>         u32 pci_flags;
>         u8 pci_segment;
> -       u32 reserved2;
> +       u32 uartclk;
>  };
>
>  /* Masks for pci_flags field above */
> --
> 2.46.0.662.g92d0881bb0-goog
>