From: Lukas Wunner <lukas@wunner.de>
To: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Cc: gregkh@linuxfoundation.org, jirislaby@kernel.org,
u.kleine-koenig@pengutronix.de, linux@armlinux.org.uk,
richard.genoud@gmail.com, nicolas.ferre@microchip.com,
alexandre.belloni@bootlin.com, ludovic.desroches@microchip.com,
shawnguo@kernel.org, s.hauer@pengutronix.de,
kernel@pengutronix.de, festevam@gmail.com, linux-imx@nxp.com,
mcoquelin.stm32@gmail.com, alexandre.torgue@foss.st.com,
linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-stm32@st-md-mailman.stormreply.com
Subject: Re: [PATCH 2 1/9] serial: core: move RS485 configuration tasks from drivers into core
Date: Thu, 17 Feb 2022 12:33:54 +0100 [thread overview]
Message-ID: <20220217113354.GA7826@wunner.de> (raw)
In-Reply-To: <20220216001803.637-2-LinoSanfilippo@gmx.de>
On Wed, Feb 16, 2022 at 01:17:55AM +0100, Lino Sanfilippo wrote:
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -1282,8 +1282,26 @@ static int uart_set_rs485_config(struct uart_port *port,
> if (copy_from_user(&rs485, rs485_user, sizeof(*rs485_user)))
> return -EFAULT;
>
> + /* pick sane settings if the user hasn't */
> + if (!(rs485.flags & SER_RS485_RTS_ON_SEND) ==
> + !(rs485.flags & SER_RS485_RTS_AFTER_SEND)) {
> + rs485.flags |= SER_RS485_RTS_ON_SEND;
> + rs485.flags &= ~SER_RS485_RTS_AFTER_SEND;
> + }
The policy you're enforcing here is: If settings are nonsensical,
always default to active-high polarity.
However some drivers currently enforce a completely different policy:
E.g. with 8250_lpc18xx.c, if SER_RS485_RTS_ON_SEND is set, use active-high
(and fix up SER_RS485_RTS_AFTER_SEND), else use active-low polarity.
This yields a different result compared to your policy in case both bits
are cleared.
Similarly, sc16is7xx.c defaults to active-low if SER_RS485_RTS_AFTER_SEND
is set, else active-high polarity. This yields a different result compared
to your policy in case both bits are set.
You risk breaking existing user space applications with this change
if those applications specify nonsensical polarity settings.
I happen to have created a similar commit to this one a month ago
and I came to the conclusion that all one can do is offer a library
function uart_sanitize_rs485_mode() which drivers may elect to call
if that helper's policy is identical to what they're doing now:
https://github.com/l1k/linux/commit/637984111e42
> +
> + rs485.delay_rts_before_send = min_t(unsigned int,
> + rs485.delay_rts_before_send,
> + SER_RS485_MAX_RTS_DELAY);
> + rs485.delay_rts_after_send = min_t(unsigned int,
> + rs485.delay_rts_after_send,
> + SER_RS485_MAX_RTS_DELAY);
Nonsensical delays may not only be passed in from user space via ioctl(),
but through the device tree. That's another reason to use a library
function: It can be called both from the ioctl() as well as after (or in)
uart_get_rs485_mode().
> + /* Return clean padding area to userspace */
> + memset(rs485.padding, 0, sizeof(rs485.padding));
Unlike the polarity and delay handling, this one makes sense.
Thanks,
Lukas
next prev parent reply other threads:[~2022-02-17 11:34 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-16 0:17 Move RS485 implementation from drivers to serial core Lino Sanfilippo
2022-02-16 0:17 ` [PATCH 2 1/9] serial: core: move RS485 configuration tasks from drivers into core Lino Sanfilippo
2022-02-17 11:33 ` Lukas Wunner [this message]
2022-02-17 21:36 ` Lino Sanfilippo
2022-02-21 18:39 ` Greg KH
2022-02-21 23:19 ` Lino Sanfilippo
2022-02-16 0:17 ` [PATCH 2 2/9] serial: amba-pl011: remove redundant code in rs485_config Lino Sanfilippo
2022-02-16 0:17 ` [PATCH 2 3/9] serial: stm32: " Lino Sanfilippo
2022-02-16 0:17 ` [PATCH 2 4/9] serial: sc16is7xx: remove redundant check " Lino Sanfilippo
2022-02-17 11:47 ` Lukas Wunner
2022-02-17 22:11 ` Lino Sanfilippo
2022-02-16 0:17 ` [PATCH 2 5/9] serial: omap: remove redundant code " Lino Sanfilippo
2022-02-16 0:18 ` [PATCH 2 6/9] serial: max310: remove redundant memset " Lino Sanfilippo
2022-02-16 0:18 ` [PATCH 2 7/9] serial: imx: remove redundant assignment " Lino Sanfilippo
2022-02-16 17:43 ` Uwe Kleine-König
2022-02-16 0:18 ` [PATCH 2 8/9] serial: fsl_lpuart: remove redundant code in rs485_config functions Lino Sanfilippo
2022-02-16 0:18 ` [PATCH 2 9/9] serial: atmel: remove redundant assignment in rs485_config Lino Sanfilippo
2022-02-17 9:22 ` Richard Genoud
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