linux-kernel - Re: [PATCH] serial: amba-pl011: Support earlycon

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Date:   Tue, 28 Apr 2020 14:54:56 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Sumit Garg <sumit.garg@...aro.org>
Cc:     dianders@...omium.org, linux-serial@...r.kernel.org,
        linux@...linux.org.uk, gregkh@...uxfoundation.org, jslaby@...e.com,
        jason.wessel@...driver.com, kgdb-bugreport@...ts.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] serial: amba-pl011: Support earlycon_kgdboc

On Fri, Apr 24, 2020 at 01:43:51PM +0530, Sumit Garg wrote:
> Implement the read() function in the early console driver. With
> recently added earlycon_kgdboc feature, this allows you to use kgdb
> to debug fairly early into the system boot.
> 
> We only bother implementing this if polling is enabled since kgdb can't
> be enabled without that.
> 
> Signed-off-by: Sumit Garg <sumit.garg@...aro.org>

Reviewed-by: Daniel Thompson <daniel.thompson@...aro.org>


> ---
> 
> Depends on kgdb patch series: https://lkml.org/lkml/2020/4/21/1179
> 
>  drivers/tty/serial/amba-pl011.c | 32 ++++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
> 
> diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c
> index 2296bb0..c010f63 100644
> --- a/drivers/tty/serial/amba-pl011.c
> +++ b/drivers/tty/serial/amba-pl011.c
> @@ -2435,6 +2435,37 @@ static void pl011_early_write(struct console *con, const char *s, unsigned n)
>  	uart_console_write(&dev->port, s, n, pl011_putc);
>  }
>  
> +#ifdef CONFIG_CONSOLE_POLL
> +static int pl011_getc(struct uart_port *port)
> +{
> +	if (readl(port->membase + UART01x_FR) & UART01x_FR_RXFE)
> +		return NO_POLL_CHAR;
> +
> +	if (port->iotype == UPIO_MEM32)
> +		return readl(port->membase + UART01x_DR);
> +	else
> +		return readb(port->membase + UART01x_DR);
> +}
> +
> +static int pl011_early_read(struct console *con, char *s, unsigned int n)
> +{
> +	struct earlycon_device *dev = con->data;
> +	int ch, num_read = 0;
> +
> +	while (num_read < n) {
> +		ch = pl011_getc(&dev->port);
> +		if (ch == NO_POLL_CHAR)
> +			break;
> +
> +		s[num_read++] = ch;
> +	}
> +
> +	return num_read;
> +}
> +#else
> +#define pl011_early_read NULL
> +#endif
> +
>  /*
>   * On non-ACPI systems, earlycon is enabled by specifying
>   * "earlycon=pl011,<address>" on the kernel command line.
> @@ -2454,6 +2485,7 @@ static int __init pl011_early_console_setup(struct earlycon_device *device,
>  		return -ENODEV;
>  
>  	device->con->write = pl011_early_write;
> +	device->con->read = pl011_early_read;
>  
>  	return 0;
>  }
> -- 
> 2.7.4
>