From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 88F3750B435; Tue, 13 Oct 2026 13:22:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791897723; cv=none; b=coFEoVBpqSYE9jjpOPf7etKAwm8dKu1XUhoxQYjDo8IHdA8GgpfjdFHjZwEc5ab2frxn78r3L9NTQcEdT2RCbL6/lW4TBTU5JH/eWu0rAxIz8dCeA08+MYMFFWS6hGqZVL/UB0YCwG2hbmiQJoO/u8aI5w8PMXn1qWwwvEW+IjI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791897723; c=relaxed/simple; bh=nKKU9Lhegzb3OComcfAvNFzjQLaUZSopiSoZfQHM/L4=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=gg/AS1pz2ss4F0pT27TkaXPJnIzmCOuY06Gw5/mz2Ptvbp7XTpYx51eoR9Y0ivyzAKFnfXb0pIzio2NL9MIz8PdJ+J8islfFhS9aA9DLUiMBIWH0wWnN3XkmhKIHEwDhWDO0TaDBARMTetVwWWeWZX7SKyJaXwCcJh+o/4D2/uY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=WtR0bx4H; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="WtR0bx4H" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9E4F31F000FF; Tue, 13 Oct 2026 13:22:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1791897722; bh=xUxtYdiU2R0c+K2lBG3528oOcrYM9dXUerJDvDBaG9g=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=WtR0bx4H9z2W9aP7CEcG+BLjG8GttUugl9WYsa6NPLhVivO8F/faHLoDH/zFEhvhM GvZGJ+BizVdHATD0FVrtmmb5AHgTmHVuXOoBQHdFC47w0MNG5jxD1oR5hRJrmuNbjv 3DEBF8+d55ikL/3mIMUETOnzzQQfa6tEKBjF8KUA= Date: Tue, 13 Oct 2026 15:22:07 +0200 From: Greg Kroah-Hartman To: Nicolai Buchwitz Cc: Russell King , Jiri Slaby , Lino Sanfilippo , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org Subject: Re: [PATCH] serial: amba-pl011: drive the bus during break in RS485 mode Message-ID: <2026101355-epidural-avenging-9249@gregkh> References: <20261011-devel-pl011-rs485-break-v1-1-62ff402378c6@tipi-net.de> Precedence: bulk X-Mailing-List: linux-serial@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20261011-devel-pl011-rs485-break-v1-1-62ff402378c6@tipi-net.de> On Sun, Oct 11, 2026 at 10:23:07PM +0200, Nicolai Buchwitz wrote: > In RS485 mode the transceiver is enabled only while data is sent. A > break set with TIOCSBRK therefore never reaches the bus, and protocols > that start each frame with a break, like DMX512, do not work. > > Handle an active break like a transmission. Enable the transceiver > before setting the break, after delay_rts_before_send if one is > configured. When the break ends, stop transmitting unless the TX path > is still sending data. > > Signed-off-by: Nicolai Buchwitz > --- > Noticed while implementing a DMX master on a CM5 with its PL011. > Tested on that board, driving a DMX512 fixture with RS485 mode left > enabled. > > The 8250 em485 code probably has the same issue. I have no hardware to > test it, but I'm happy to send a patch if someone is willing to. > --- > drivers/tty/serial/amba-pl011.c | 69 +++++++++++++++++++++++++++++++++++++++-- > 1 file changed, 67 insertions(+), 2 deletions(-) > > diff --git a/drivers/tty/serial/amba-pl011.c b/drivers/tty/serial/amba-pl011.c > index fcfa9f00aec6..7bef1be5e9b4 100644 > --- a/drivers/tty/serial/amba-pl011.c > +++ b/drivers/tty/serial/amba-pl011.c > @@ -327,6 +327,7 @@ struct uart_amba_port { > char type[12]; > ktime_t rs485_tx_drain_interval; /* nano */ > enum pl011_rs485_tx_state rs485_tx_state; > + bool rs485_break; > struct hrtimer trigger_start_tx; > struct hrtimer trigger_stop_tx; > bool console_line_ended; > @@ -1279,6 +1280,11 @@ static inline bool pl011_dma_rx_running(struct uart_amba_port *uap) > return uap->using_rx_dma && uap->dmarx.running; > } > > +static inline bool pl011_dma_tx_queued(struct uart_amba_port *uap) > +{ > + return uap->dmatx.queued; > +} > + > #else > /* Blank functions if the DMA engine is not available */ > static inline void pl011_dma_remove(struct uart_amba_port *uap) > @@ -1330,6 +1336,11 @@ static inline bool pl011_dma_rx_running(struct uart_amba_port *uap) > return false; > } > > +static inline bool pl011_dma_tx_queued(struct uart_amba_port *uap) > +{ > + return false; > +} > + > #define pl011_dma_flush_buffer NULL > #endif > > @@ -1357,6 +1368,10 @@ static void pl011_rs485_tx_stop(struct uart_amba_port *uap) > { > struct uart_port *port = &uap->port; > > + /* pl011_break_ctl() stops the transmission when the break ends */ > + if (uap->rs485_break) > + return; > + > if (uap->rs485_tx_state == SEND) > uap->rs485_tx_state = WAIT_AFTER_SEND; > > @@ -1477,8 +1492,12 @@ static enum hrtimer_restart pl011_trigger_start_tx(struct hrtimer *t) > unsigned long flags; > > uart_port_lock_irqsave(&uap->port, &flags); > - if (uap->rs485_tx_state == WAIT_AFTER_RTS) > - pl011_start_tx(&uap->port); > + if (uap->rs485_tx_state == WAIT_AFTER_RTS) { > + uap->rs485_tx_state = SEND; > + /* A break can arm the timer while TX is stopped */ > + if (!uart_tx_stopped(&uap->port)) > + pl011_start_tx(&uap->port); > + } > uart_port_unlock_irqrestore(&uap->port, flags); > > return HRTIMER_NORESTART; > @@ -1770,16 +1789,60 @@ static void pl011_break_ctl(struct uart_port *port, int break_state) > { > struct uart_amba_port *uap = > container_of(port, struct uart_amba_port, port); > + struct tty_port *tport = &port->state->port; > + bool rs485 = port->rs485.flags & SER_RS485_ENABLED; > unsigned long flags; > unsigned int lcr_h; > > uart_port_lock_irqsave(&uap->port, &flags); > + > + /* > + * In RS485 mode the transceiver only drives the bus while > + * transmitting. Treat a break as a transmission. > + */ > + if (rs485 && break_state == -1 && !uap->rs485_break) { > + uap->rs485_break = true; > + > + /* Pending data already enabled the transceiver */ > + if (uap->rs485_tx_state != SEND && > + uap->rs485_tx_state != WAIT_AFTER_RTS) > + pl011_rs485_tx_start(uap); > + > + /* > + * Wait out delay_rts_before_send before starting the break. > + * The state stays WAIT_AFTER_RTS, so the TX path behaves as > + * without a break. Start it here if trigger_start_tx is late. > + */ > + if (uap->rs485_tx_state == WAIT_AFTER_RTS) { > + uart_port_unlock_irqrestore(&uap->port, flags); > + msleep(port->rs485.delay_rts_before_send); > + uart_port_lock_irqsave(&uap->port, &flags); > + > + if (uap->rs485_tx_state == WAIT_AFTER_RTS) { > + hrtimer_try_to_cancel(&uap->trigger_start_tx); > + uap->rs485_tx_state = SEND; > + if (!uart_tx_stopped(port)) > + pl011_start_tx(port); > + } > + } > + } > + > lcr_h = pl011_read(uap, REG_LCRH_TX); > if (break_state == -1) > lcr_h |= UART01x_LCRH_BRK; > else > lcr_h &= ~UART01x_LCRH_BRK; > pl011_write(lcr_h, uap, REG_LCRH_TX); > + > + if (break_state == 0 && uap->rs485_break) { > + uap->rs485_break = false; > + /* An active TX path stops the transmission when it is done */ > + if (rs485 && (uart_tx_stopped(port) || > + (!pl011_dma_tx_queued(uap) && > + kfifo_is_empty(&tport->xmit_fifo)))) > + pl011_rs485_tx_stop(uap); > + } > + > uart_port_unlock_irqrestore(&uap->port, flags); > } > > @@ -2100,6 +2163,7 @@ static void pl011_shutdown(struct uart_port *port) > hrtimer_cancel(&uap->trigger_stop_tx); > > uart_port_lock_irq(port); > + uap->rs485_break = false; > if (uap->rs485_tx_state != OFF) > pl011_rs485_tx_stop_now(uap); > uart_port_unlock_irq(port); > @@ -2396,6 +2460,7 @@ static int pl011_rs485_config(struct uart_port *port, struct ktermios *termios, > struct uart_amba_port *uap = > container_of(port, struct uart_amba_port, port); > > + uap->rs485_break = false; > if (port->rs485.flags & SER_RS485_ENABLED) > pl011_rs485_tx_stop(uap); > > > --- > base-commit: 36844ea19656fb41278799ef3d5cd52120d89149 > change-id: 20261011-devel-pl011-rs485-break-bec3b979a420 Does not apply to the tty-testing branch :(