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    SubjectRe: [RFC] With 8250 Designware UART, if writes to the LCR failed the kernel will hung up
    Hi Zhang,

    On 03/06/2015 04:11 AM, Zhang Zhen wrote:
    > Hi,
    >
    > I'm testing 4.0-rc1 kernel on my board with 8250 Designware UART.(ARM Cortex-a15 single core).
    >
    > I found if serial is busy and writes to the LCR failed after tried 1000 times.
    > The kernel will hung up.
    >
    > The system boot success after changed from:
    >
    > 95 static void dw8250_serial_out(struct uart_port *p, int offset, int value)
    > 96 {
    > 97 struct dw8250_data *d = p->private_data;
    > 98
    > ...
    > ...
    > 112 writeb(value, p->membase + (UART_LCR << p->regshift));
    > 113 }
    > 114 dev_err(p->dev, "Couldn't set LCR to %d\n", value);
    > 115 }
    > 116 }
    >
    > to:
    >
    > 95 static void dw8250_serial_out(struct uart_port *p, int offset, int value)
    > 96 {
    > 97 struct dw8250_data *d = p->private_data;
    > 98
    > ...
    > ...
    > 112 writeb(value, p->membase + (UART_LCR << p->regshift));
    > 113 }
    > 114 dev_info(p->dev, "Couldn't set LCR to %d\n", value); //changed here
    > 115 }
    > 116 }
    >
    > The reason is serial8250_console_write can't get port->lock because serial8250_do_set_termios has
    > got port->lock.
    > So i think here we should change from dev_err to dev_info ?

    That's not really going to help because this will still hang if the
    console_loglevel is set to < KERN_INFO.

    > Any suggestions are welcome.

    Check that the port is not the uart_console() before logging the error,
    like;

    if (!uart_console(p))
    dev_err(p->dev, "Couldn't .....");

    Use a global flag to note the error and check it from other contexts.
    Plus, find out why you can't write LCR there.

    Also, consider re-designing how the 8250_dw driver implements that
    "feature".

    Regards,
    Peter Hurley


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