From: Peter Hurley <peter@hurleysoftware.com>
To: "Matwey V. Kornilov" <matwey@sai.msu.ru>
Cc: Greg KH <gregkh@linuxfoundation.org>,
jslaby@suse.com, linux-serial@vger.kernel.org,
linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 3/3] tty: Add software emulated RS485 support for 8250
Date: Mon, 9 Nov 2015 09:40:49 -0500 [thread overview]
Message-ID: <5640B071.8000806@hurleysoftware.com> (raw)
In-Reply-To: <CAJs94EaWQSqqUzqRoXO=vfBCf7CE+0Gt8C5-zGOB=t6ND0bSBg@mail.gmail.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>:
>> Hi Matwey,
>>
>> On 11/07/2015 05:09 AM, Matwey V. Kornilov wrote:
>>> Implementation of software emulation of RS485 direction handling is based
>>> on omap-serial driver. It is acts as the following. At transmission start,
>>> RTS is set (if required) and receiver is off (if required). At transmission
>>> stop, RTS is set (if required) and fifo is flushed.
>>
>> Comments below.
>>
>>> Signed-off-by: Matwey V. Kornilov <matwey@sai.msu.ru>
>>> ---
>>> drivers/tty/serial/8250/8250_port.c | 32 ++++++++++++++++++++++++++++++++
>>> 1 file changed, 32 insertions(+)
>>>
>>> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
>>> index 52d82d2..a9291f7 100644
>>> --- a/drivers/tty/serial/8250/8250_port.c
>>> +++ b/drivers/tty/serial/8250/8250_port.c
>>> @@ -559,7 +559,37 @@ static void serial8250_rpm_put_tx(struct uart_8250_port *p)
>>> pm_runtime_mark_last_busy(p->port.dev);
>>> pm_runtime_put_autosuspend(p->port.dev);
>>> }
>>
>> Newline req'd here.
>>
>>> +static void serial8250_stop_rx(struct uart_port *port);
>>
>> You can eliminate this forward decl by relocating serial8250_stop_rx() to here
>> (in a separate patch).
>>
>>> +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.
Regards,
Peter Hurley
>>> + }
>>> + if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
>>> + serial8250_stop_rx(&p->port);
>>> +}
>>
>> Newline req'd here.
>>
>>> +static void serial8250_rs485_stop_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_AFTER_SEND) {
>>> + if (p->port.rs485.delay_rts_after_send > 0)
>>> + mdelay(p->port.rs485.delay_rts_after_send);
>>
>> Same issue with irqs off.
>>
>>> + serial_port_out(&p->port, UART_MCR, UART_MCR_RTS);
>>> + }
>>> + /*
>>> + * Empty the RX FIFO, we are not interested in anything
>>> + * received during the half-duplex transmission.
>>> + */
>>> + if (!(p->port.rs485.flags & SER_RS485_RX_DURING_TX))
>>> + serial8250_clear_fifos(p);
>>> +}
>>> /*
>>> * IER sleep support. UARTs which have EFRs need the "extended
>>> * capability" bit enabled. Note that on XR16C850s, we need to
>>> @@ -1309,6 +1339,7 @@ static void serial8250_stop_tx(struct uart_port *port)
>>> up->acr |= UART_ACR_TXDIS;
>>> serial_icr_write(up, UART_ACR, up->acr);
>>> }
>>> + serial8250_rs485_stop_tx(up);
>>> serial8250_rpm_put(up);
>>> }
>>>
>>> @@ -1317,6 +1348,7 @@ static void serial8250_start_tx(struct uart_port *port)
>>> struct uart_8250_port *up = up_to_u8250p(port);
>>>
>>> serial8250_rpm_get_tx(up);
>>> + serial8250_rs485_start_tx(up);
>>>
>>> if (up->dma && !up->dma->tx_dma(up))
>>> return;
>>>
>>
>
>
>
next prev parent reply other threads:[~2015-11-09 14:40 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-07 10:09 [PATCH v2 1/3] tty: Introduce UART_CAP_HW485 Matwey V. Kornilov
2015-11-07 10:09 ` [PATCH v2 2/3] tty: Implement default fallback serial8250_rs485_config Matwey V. Kornilov
2015-11-07 12:29 ` Peter Hurley
2015-11-07 13:51 ` Matwey V. Kornilov
2015-11-07 14:20 ` Peter Hurley
2015-11-07 10:09 ` [PATCH v2 3/3] tty: Add software emulated RS485 support for 8250 Matwey V. Kornilov
2015-11-07 16:03 ` Peter Hurley
2015-11-08 10:52 ` Matwey V. Kornilov
2015-11-09 14:40 ` Peter Hurley [this message]
2015-11-09 15:45 ` Matwey V. Kornilov
2015-11-09 21:30 ` Peter Hurley
2015-11-09 21:43 ` Matwey V. Kornilov
2015-11-09 22:05 ` Peter Hurley
2015-11-10 11:35 ` Matwey V. Kornilov
2015-11-10 16:12 ` Peter Hurley
2015-11-10 16:25 ` Matwey V. Kornilov
2015-11-10 16:52 ` Peter Hurley
2015-11-12 12:34 ` Matwey V. Kornilov
2015-11-12 13:35 ` Peter Hurley
2015-11-13 8:35 ` Matwey V. Kornilov
2015-11-07 12:22 ` [PATCH v2 1/3] tty: Introduce UART_CAP_HW485 Peter Hurley
2015-11-07 12:39 ` Matwey V. Kornilov
2015-11-07 15:32 ` Peter Hurley
2015-11-07 21:10 ` Matwey V. Kornilov
2015-11-07 22:04 ` Peter Hurley
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