Messages in this thread | | | Subject | Re: [PATCH v2 3/3] tty: Add software emulated RS485 support for 8250 | From | Peter Hurley <> | Date | Mon, 9 Nov 2015 16:30:48 -0500 |
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On 11/09/2015 10:45 AM, Matwey V. Kornilov wrote: > 2015-11-09 17:40 GMT+03:00 Peter Hurley <peter@hurleysoftware.com>: >> On 11/08/2015 05:52 AM, Matwey V. Kornilov wrote: >>> 2015-11-07 19:03 GMT+03:00 Peter Hurley <peter@hurleysoftware.com>: >>>> On 11/07/2015 05:09 AM, Matwey V. Kornilov wrote:
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>>>>> +static void serial8250_rs485_start_tx(struct uart_8250_port *p) >>>>> +{ >>>>> + if (p->capabilities & UART_CAP_HW485 || !(p->port.rs485.flags & SER_RS485_ENABLED)) >>>>> + return; >>>>> + >>>>> + if (p->port.rs485.flags & SER_RS485_RTS_ON_SEND) { >>>>> + serial_port_out(&p->port, UART_MCR, UART_MCR_RTS); >>>>> + if (p->port.rs485.delay_rts_before_send > 0) >>>>> + mdelay(p->port.rs485.delay_rts_before_send); >>>> >>>> So irqs are off for x msecs, and this cpu can't be used for anything else now? >>>> I think this needs to be solved differently; maybe with a timer? >>> >>> Call of serial8250_start_tx is wrapped with spin_lock_irq in serial_core.c:2154 >> >> Yep, which is why I pointed out "irqs are off for x msecs". >> >>> I've tried to use msleep instead of mdelay but got "BUG: scheduling >>> while atomic". >> >> Right, can't sleep while irqs are off, which is why I suggested something >> like a timer. > > I am not sure that understand you correctly. Do you think that the > following would be ok? > > wait_queue_head_t wait; > init_waitqueue_head(&wait); > wait_event_timeout(wait, 0, p->port.rs485.delay_rts_before_send * HZ / 1000);
Except for spinning, there is no way to wait-in-place with irqs off.
You'll need to do something more complex, like 1. raise RTS 2. start a timer _and return early without starting tx_ 3. timer goes off, handler actually starts tx
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