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Date: Thu, 17 Dec 2015 08:29:03 -0800
From: Peter Hurley <peter@...leysoftware.com>
To: Sebastian Frias <sf84@...oste.net>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-serial@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
mason <slash.tmp@...e.fr>,
Måns Rullgård <mans@...sr.com>
Subject: Re: [RFC PATCH] always probe UART HW when options are not specified
On 12/17/2015 07:15 AM, Sebastian Frias wrote:
> ---
>
> I think there are a few minor bugs on the 8250 UART code.
>
> Below you can find a patch with a proposed solution.
>
> In a nutshell:
> - probe_baud from 87515772c33ee8a0cc08d984a7d2401eeff074cd was
> converted into probe_port so that it reads all the parameters that
> uart_set_options require (namely baud, parity, bits, flow).
> - reading/writing to UART_DLL/UART_DLM directly are converted to
> using the read_dl/write_dl callbacks.
> - the port is always probed if there are no options (*).
Because I don't want to probe the port at all.
But must when using the
earlycon=ttyS0,....
command-line (because the original hack expects that behavior).
Regards,
Peter Hurley
> (*): I'm not sure why commit 87515772c33ee8a0cc08d984a7d2401eeff074cd
> makes a difference in that regard, especially considering the commit
> log states that if there are no options, the hardware is assumed to
> be already initialised. Since uart_set_options is always called, the
> current hardware setup could be overwritten with different parameters
> if the actual hardware is not probed.
>
> ---
> drivers/tty/serial/8250/8250_core.c | 84 ++++++++++++++++++++++++++---------
> 1 file changed, 63 insertions(+), 21 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> index 2c46a21..624667f 100644
> --- a/drivers/tty/serial/8250/8250_core.c
> +++ b/drivers/tty/serial/8250/8250_core.c
> @@ -791,22 +791,19 @@ static int size_fifo(struct uart_8250_port *up)
> */
> static unsigned int autoconfig_read_divisor_id(struct uart_8250_port *p)
> {
> - unsigned char old_dll, old_dlm, old_lcr;
> + unsigned char old_lcr;
> unsigned int id;
> + unsigned int old_dl;
>
> old_lcr = serial_in(p, UART_LCR);
> - serial_out(p, UART_LCR, UART_LCR_CONF_MODE_A);
> -
> - old_dll = serial_in(p, UART_DLL);
> - old_dlm = serial_in(p, UART_DLM);
>
> - serial_out(p, UART_DLL, 0);
> - serial_out(p, UART_DLM, 0);
> + serial_out(p, UART_LCR, UART_LCR_CONF_MODE_A);
>
> - id = serial_in(p, UART_DLL) | serial_in(p, UART_DLM) << 8;
> + old_dl = serial_dl_read(p);
> + serial_dl_write(p, 0);
> + id = serial_dl_read(p);
> + serial_dl_write(p, old_dl);
>
> - serial_out(p, UART_DLL, old_dll);
> - serial_out(p, UART_DLM, old_dlm);
> serial_out(p, UART_LCR, old_lcr);
>
> return id;
> @@ -3440,22 +3437,67 @@ static void univ8250_console_write(struct console *co, const char *s,
> serial8250_console_write(up, s, count);
> }
>
> -static unsigned int probe_baud(struct uart_port *port)
> +static int probe_port(struct uart_port *port, int *parity, int *bits, int *flow)
> {
> - unsigned char lcr, dll, dlm;
> + struct uart_8250_port *up = up_to_u8250p(port);
> + unsigned char lcr, efr;
> unsigned int quot;
>
> lcr = serial_port_in(port, UART_LCR);
> serial_port_out(port, UART_LCR, lcr | UART_LCR_DLAB);
> - dll = serial_port_in(port, UART_DLL);
> - dlm = serial_port_in(port, UART_DLM);
> + quot = serial_dl_read(up);
> + serial_port_out(port, UART_LCR, UART_LCR_CONF_MODE_B);
> + if (port->flags & UPF_EXAR_EFR)
> + efr = serial_port_in(port, UART_XR_EFR);
> + else
> + efr = serial_port_in(port, UART_EFR);
> serial_port_out(port, UART_LCR, lcr);
>
> - quot = (dlm << 8) | dll;
> - return (port->uartclk / 16) / quot;
> +//word length select mask
> +#define WLS_MASK (0x3)
> +//parity enable
> +#define PEN (0x8)
> +//even parity select
> +#define EPS (0x10)
> +
> + switch (lcr & WLS_MASK) {
> + case 0: // 5bits
> + case 1: // 6bits
> + // Not supported by drivers/tty/serial/serial_core.c:uart_set_options() anyway
> + WARN(true, "%s: probed uart word length (%u bits) is not supported by uart_set_options()\n", __FUNCTION__, (lcr & WLS_MASK) ? 5 : 6 );
> + break;
> + case 2: // 7bits
> + *bits = 7;
> + break;
> + case 3: // 8bits
> + *bits = 8;
> + break;
> + };
> +
> + if (lcr & PEN)
> + {
> + if (lcr & EPS)
> + *parity = 'e';
> + else
> + *parity = 'o';
> + }
> + else
> + *parity = 'n';
> +
> + if (efr & UART_EFR_CTS)
> + *flow = 'r';
> + else
> + *flow = 'n';
> +
> + if (quot)
> + return (port->uartclk / 16) / quot;
> + else
> + WARN(true, "%s: quot is zero!\n", __FUNCTION__);
> +
> + return -1;
> }
>
> -static int serial8250_console_setup(struct uart_port *port, char *options, bool probe)
> +static int serial8250_console_setup(struct uart_port *port, char *options)
> {
> int baud = 9600;
> int bits = 8;
> @@ -3467,8 +3509,8 @@ static int serial8250_console_setup(struct uart_port *port, char *options, bool
>
> if (options)
> uart_parse_options(options, &baud, &parity, &bits, &flow);
> - else if (probe)
> - baud = probe_baud(port);
> + else
> + baud = probe_port(port, &parity, &bits, &flow);
>
> return uart_set_options(port, port->cons, baud, parity, bits, flow);
> }
> @@ -3488,7 +3530,7 @@ static int univ8250_console_setup(struct console *co, char *options)
> /* link port to console */
> port->cons = co;
>
> - return serial8250_console_setup(port, options, false);
> + return serial8250_console_setup(port, options);
> }
>
> /**
> @@ -3537,7 +3579,7 @@ static int univ8250_console_match(struct console *co, char *name, int idx,
>
> co->index = i;
> port->cons = co;
> - return serial8250_console_setup(port, options, true);
> + return serial8250_console_setup(port, options);
> }
>
> return -ENODEV;
> --
> 1.7.10.4
>
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