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Message-ID: <CACQ1gAiDzgzB4EbKqPJi66TG0848kJR5TmyCUAehkz_81bVNQA@mail.gmail.com>
Date: Wed, 14 Sep 2016 12:31:43 +0200
From: Richard Genoud <richard.genoud@...il.com>
To: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc: Cyrille Pitchen <cyrille.pitchen@...el.com>,
Nicolas Ferre <nicolas.ferre@...el.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2 3/3] tty/serial: at91: fix hardware handshake on SAM9x5
(without GPIOs)
2016-09-13 15:45 GMT+02:00 Alexandre Belloni
<alexandre.belloni@...e-electrons.com>:
> On 12/09/2016 at 12:50:38 +0200, Richard Genoud wrote :
>> >> diff --git a/drivers/tty/serial/atmel_serial.c b/drivers/tty/serial/atmel_serial.c
>> >> index e9b4fbf88c2d..32154e7231ce 100644
>> >> --- a/drivers/tty/serial/atmel_serial.c
>> >> +++ b/drivers/tty/serial/atmel_serial.c
>> >> @@ -2130,15 +2130,19 @@ static void atmel_set_termios(struct uart_port *port, struct ktermios *termios,
>> >> } else if ((termios->c_cflag & CRTSCTS) &&
>> >> !mctrl_gpio_use_rtscts(atmel_port->gpios)) {
>> >> /*
>> >> - * RS232 with hardware handshake (RTS/CTS)
>> >> - * handled by the controller.
>> >> + * Automatic hardware handshake (RTS/CTS) only work with
>> >> + * FIFOs or PDC.
>> >> + * Meaning that on SAM9x5 the controller can't handle
>> >> + * the hardware handshake (no FIFOs nor PDC on these platforms).
>> >> */
>> >> - if (atmel_use_dma_rx(port) && !atmel_use_fifo(port)) {
>> >> - dev_info(port->dev, "not enabling hardware flow control because DMA is used");
>> >> - termios->c_cflag &= ~CRTSCTS;
>> >> - } else {
>> >> + if (atmel_use_pdc_rx(port) || atmel_use_fifo(port))
>> >> mode |= ATMEL_US_USMODE_HWHS;
>> >> - }
>> >> + else
>> >> + /*
>> >> + * The hardware handshake won't be handle by the
>> >> + * controller but by the driver.
>> >> + */
>> >> + mode |= ATMEL_US_USMODE_NORMAL;
>> >
>> > You still need the case where HWHS is impossible and there are no gpio
>> > configured. You need to inform userspace that the configuration was not
>> > applied instead of silently ignoring the error.
>>
>> Could you explain which case it is ?
>> The only one I can see is when there's no GPIO declared for RTS/CTS
>> AND, there's no pin muxed for RTS/CTS either.
>>
>> Have you got another example in mind ?
>>
>
> Hum, actually, it is that case. The other one (CRTSCTS and gpios) is
> handled in the else below. I think you need to keep the termios->c_cflag
> &= ~CRTSCTS; here so that userspace knows configuring it failed.
So, could you explain how you intend to detect that there's no pin
muxed for RTS/CTS ?
Because IHMO, that's not possible with what is described in the DTS.
To be sure that we really understand each other, I want you to tell me
how you intend to make the difference between:
pinctrl-0 = <&pinctrl_usart1 &pinctrl_usart1_rts_cts>;
AND
pinctrl-0 = <&pinctrl_usart1>;
in the atmel_serial driver ?
and then your test would be:
if (rts_cts_not_muxed()) {
dev_info(port->dev, "hey ! there's no pin muxed for RTS/CTS, I won't
enable HWHS");
}
Meanwhile, I did quite some testing with a sama5d3 xplained I have.
Same results as the SAM9x5. (Unfortunately, I don't have a sama5d2,
the only ones with fifos).
Here are those results:
With RTS/CTS NOT handled by GPIOs (pinctrl-0 = <&pinctrl_usart1
&pinctrl_usart1_rts_cts>;) :
- if USMODE==HW : Fails in every case. (DMA/PDC/PIO)
- if USMODE==NORMAL + PDC : crask kernel (quite normal since there's no PDC)
- if USMODE==NORMAL + DMA : works great, CTS and RTS respond OK
- if USMODE==NORMAL + PIO : works fine, but some chars gets eaten.
With RTS/CTS handled by GPIOs
(pinctrl-0 = <&pinctrl_usart1;rts-gpios = <&pioB 27
GPIO_ACTIVE_LOW>;cts-gpios = <&pioB 26 GPIO_ACTIVE_LOW>;) :
- if USMODE==HW : Nonsense
- if USMODE==NORMAL + PDC : crask kernel (quite normal since there's no PDC)
- if USMODE==NORMAL + DMA : works great, CTS and RTS respond OK
- if USMODE==NORMAL + PIO : works fine, but some chars gets eaten.
So, again, commit 5be605ac9af9 is wrong because we don't want to
remove the CRTSCTS flag if rts_cts are muxed !!!
If someone does some testing on a sama5d2, it would help, but from the
informations I have, I stick to this logic:
/*
* Automatic hardware handshake (RTS/CTS) only work with
* FIFOs or PDC.
* Meaning that on SAM9x5 the controller can't handle
* the hardware handshake (no FIFOs nor PDC on these platforms).
*/
if (atmel_use_pdc_rx(port) || atmel_use_fifo(port))
mode |= ATMEL_US_USMODE_HWHS;
else
/*
* The hardware handshake won't be handle by the
* controller but by the driver.
*/
mode |= ATMEL_US_USMODE_NORMAL;
Test configuration on 3xplained :
DTS:
usart1: serial@...20000 {
compatible = "atmel,at91sam9260-usart";
reg = <0xf0020000 0x100>;
interrupts = <13 IRQ_TYPE_LEVEL_HIGH 5>;
atmel,use-dma-rx; // comment to switch to PIO
dmas = <&dma0 2 AT91_DMA_CFG_PER_ID(5)>, <&dma0 2
(AT91_DMA_CFG_PER_ID(6) | AT91_DMA_CFG_FIFOCFG_ASAP)>;
dma-names = "tx", "rx";
pinctrl-names = "default";
clocks = <&usart1_clk>;
clock-names = "usart";
pinctrl-0 = <&pinctrl_usart1 &pinctrl_usart1_rts_cts>;
/*
//or
rts-gpios = <&pioB 27 GPIO_ACTIVE_LOW>;
cts-gpios = <&pioB 26 GPIO_ACTIVE_LOW>;
pinctrl-0 = <&pinctrl_usart1>;
*/
status = "okay";
};
usart2: serial@...20000 {
compatible = "atmel,at91sam9260-usart";
reg = <0xf8020000 0x100>;
interrupts = <14 IRQ_TYPE_LEVEL_HIGH 5>;
atmel,use-dma-rx;
dmas = <&dma1 2 AT91_DMA_CFG_PER_ID(7)>, <&dma1 2
(AT91_DMA_CFG_PER_ID(8) | AT91_DMA_CFG_FIFOCFG_ASAP)>;
rts-gpios = <&pioA 20 GPIO_ACTIVE_LOW>;
cts-gpios = <&pioA 21 GPIO_ACTIVE_LOW>;
dma-names = "tx", "rx";
pinctrl-names = "default";
pinctrl-0 = <&pinctrl_usart2>;
clocks = <&usart2_clk>;
clock-names = "usart";
status = "okay";
};
On board:
stty -F /dev/ttyS2 115200 raw -echo crtscts -opost clocal cread
stty -F /dev/ttyS3 115200 raw -echo crtscts -opost clocal cread
On one terminal :
cat MAINTAINERS > /dev/ttyS3
On another:
exec 4</dev/ttyS2
cat <&4 >> /tmp/rcv # ctrl-c and again several times
exec 4<&-
diff -u MAINTAINERS /tmp/rcv
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