Re: [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