On 2015/3/10 10:47, Tim Kryger wrote: > On Mon, Mar 9, 2015 at 8:05 AM, Alan Cox <alan@xxxxxxxxxxxxxxx> wrote: > >> Ah no - I meant what is their official software workaround for existing >> parts with the bug ? Presumably they have an errata document that >> discusses this and the correct methods they recommend to avoid the >> hang ? > > As far as I know, the only advice they provided was rather naive. > > The documentation I saw suggested stashing a copy of the LCR and then > rewriting it when the special LCR write failed interrupt was raised. > > That approach was not workable as the LCR might be written while the > interrupt is masked causing the sequence of register writes to occur > in an order other than what was desired. > > Additionally, when the LCR needed to be re-written but the UART stayed > busy, the interrupt would keep firing and the driver would starve out > everything else on the CPU. > > The current workaround of clearing fifos and retrying a fixed number > of times isn't ideal but I'm not sure what else can be done given the > way this hardware works. > > Additional background is in c49436b657d0a56a6ad90d14a7c3041add7cf64d > Hi, If writes to the LCR failed and the dev_err in dw8250_serial_out lead to the system hung up. The root cause is that serial8250_console_write try to get port->lock which has been got by serial8250_do_set_termios. "Writes to the LCR are used to change the baud rate, parity, stop bit, or data length so the data that may be lost is likely not important." The dev_err in dw8250_serial_out must be needed? We can delete dev_err directly ? Best regards! > -Tim > > . > -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
