linux-kernel - Re: [PATCH v3 1/2] earlycon: Let users set the clock frequency

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Message-ID: <CANiDSCs-CdhdvZF1PsDWivWiTB-=66DK4XOrv5hzbgbC9Z=+Rg@mail.gmail.com>
Date:   Fri, 2 Dec 2022 18:24:19 +0100
From:   Ricardo Ribalda <ribalda@...omium.org>
To:     Jonathan Corbet <corbet@....net>,
        Jiri Slaby <jirislaby@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-serial@...r.kernel.org
Subject: Re: [PATCH v3 1/2] earlycon: Let users set the clock frequency

Hi Jiri

is there something else that I am missing here?

Thanks!

On Thu, 24 Nov 2022 at 13:39, Ricardo Ribalda <ribalda@...omium.org> wrote:
>
> Some platforms, namely AMD Picasso, use non standard uart clocks (48M),
> witch makes it impossible to use with earlycon.
>
> Let the user select its own frequency.
>
> Signed-off-by: Ricardo Ribalda <ribalda@...omium.org>
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index a465d5242774..9efb6c3b0486 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1182,10 +1182,10 @@
>                         specified, the serial port must already be setup and
>                         configured.
>
> -               uart[8250],io,<addr>[,options]
> -               uart[8250],mmio,<addr>[,options]
> -               uart[8250],mmio32,<addr>[,options]
> -               uart[8250],mmio32be,<addr>[,options]
> +               uart[8250],io,<addr>[,options[,uartclk]]
> +               uart[8250],mmio,<addr>[,options[,uartclk]]
> +               uart[8250],mmio32,<addr>[,options[,uartclk]]
> +               uart[8250],mmio32be,<addr>[,options[,uartclk]]
>                 uart[8250],0x<addr>[,options]
>                         Start an early, polled-mode console on the 8250/16550
>                         UART at the specified I/O port or MMIO address.
> @@ -1194,7 +1194,9 @@
>                         If none of [io|mmio|mmio32|mmio32be], <addr> is assumed
>                         to be equivalent to 'mmio'. 'options' are specified
>                         in the same format described for "console=ttyS<n>"; if
> -                       unspecified, the h/w is not initialized.
> +                       unspecified, the h/w is not initialized. 'uartclk' is
> +                       the uart clock frequency; if unspecified, it is set
> +                       to 'BASE_BAUD' * 16.
>
>                 pl011,<addr>
>                 pl011,mmio32,<addr>
> diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c
> index a5f380584cda..3a0c88419b6c 100644
> --- a/drivers/tty/serial/earlycon.c
> +++ b/drivers/tty/serial/earlycon.c
> @@ -120,7 +120,13 @@ static int __init parse_options(struct earlycon_device *device, char *options)
>         }
>
>         if (options) {
> +               char *uartclk;
> +
>                 device->baud = simple_strtoul(options, NULL, 0);
> +               uartclk = strchr(options, ',');
> +               if (uartclk && kstrtouint(uartclk + 1, 0, &port->uartclk) < 0)
> +                       pr_warn("[%s] unsupported earlycon uart clkrate option\n",
> +                               options);
>                 length = min(strcspn(options, " ") + 1,
>                              (size_t)(sizeof(device->options)));
>                 strscpy(device->options, options, length);
> @@ -139,7 +145,8 @@ static int __init register_earlycon(char *buf, const struct earlycon_id *match)
>                 buf = NULL;
>
>         spin_lock_init(&port->lock);
> -       port->uartclk = BASE_BAUD * 16;
> +       if (!port->uartclk)
> +               port->uartclk = BASE_BAUD * 16;
>         if (port->mapbase)
>                 port->membase = earlycon_map(port->mapbase, 64);
>
>
> --
> b4 0.11.0-dev-d93f8



-- 
Ricardo Ribalda