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 CFA45407CF4; Thu, 9 Jul 2026 10:41:05 +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=1783593667; cv=none; b=R8lprzlY5Sz4q4kHBFPxPiCHxyrpOLD/pAJI1V0hFyOvrZaFqRwTns/Ko+SZyWiuebnZZOwy3EVNNk128DtWeSzFtt/JBSN9mhNWHG5dsHDL8RdohcfdR1ND2DvjzKsC0SSMMqPgawWRVR9Zkj0ejYENszjnAy4GdpUJssjle5A= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1783593667; c=relaxed/simple; bh=/UYcyk4xSHZW2Za0icB5gjH5AfgATKKeiMDzb2mPIJQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=jPxhPrMh3zlIECc07Mfe+5p7POmuquFJlAz9HjAQE6WT0ihzp7cIpEK+blRejHUKEpeNUNO1hfxxEoIvfkEw4NP/TxPfIYPQQf16nElHelCKDr3wCHV3Pp8y5DVJfpQ0LbyGcNeBT0aL5/lOve7K7cIhUTmudStqMU9J0kwZO58= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=STkRj/LJ; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="STkRj/LJ" Received: by smtp.kernel.org (Postfix) with ESMTPSA id D3E7A1F000E9; Thu, 9 Jul 2026 10:41:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1783593665; bh=Ok8nCG+5ZUFZj4SNj3aC5QZ5vEPt/YStIDSNq8/fAF4=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=STkRj/LJzMV0y33mat/04iL/Rkp9jnDa3B37IZtIN4rJZrUZc3xZijpHBNGMCVJQQ JosSQ6bPHF2MqwrsNxG+Kqh06g6Zrh3OFM2uLjiDinxxiHmeq0NH33uslRWHXTC3/w o2rYidt8u3440u3k+mQUh7VQsDWKHdZ4oswBxhmzDfOzZd38dIZTYOKW0ocwebHlvO DolFRIp+SWmeduVF8/YY+8zOW5vHGI/h0RXtcmiuXrpoeESQ99Gwe9szLR7yl0ai/X dAKS+GrEpwow5fzTnRBGoR8PtlqhN/PogcYBZmDEbm5rbzqH5mWXzpWkgYHP/jTxct bAiOINJDJykmQ== Message-ID: <158e6123-46fe-4a8c-9de4-093009a22a02@kernel.org> Date: Thu, 9 Jul 2026 12:41:03 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] serial: max310x: drive RTS in software when hardware delays are too short To: Tapio Reijonen , Greg Kroah-Hartman Cc: linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org References: <20260709-max310x-rs485-sw-delay-v1-1-454ac10b937a@vaisala.com> Content-Language: en-US From: Jiri Slaby Autocrypt: addr=jirislaby@kernel.org; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 09. 07. 26, 10:46, Tapio Reijonen wrote: > max310x_rs485_config() rejected delay_rts_before_send and > delay_rts_after_send values larger than 0x0f with -ERANGE, which made > the UART core wipe port->rs485 in uart_rs485_config() and silently > disable RS485. The HDPIXDELAY register holds the setup and hold > delays in 4-bit-per-direction bit-times, so even values inside that > range only encode a fraction of a millisecond at typical baud rates > and the chip's hardware auto-RTS path cannot cover the millisecond > range the kernel UART layer expresses. ... > --- a/drivers/tty/serial/max310x.c > +++ b/drivers/tty/serial/max310x.c ... > @@ -324,6 +345,21 @@ static struct uart_driver max310x_uart = { > > static DECLARE_BITMAP(max310x_lines, MAX310X_UART_NRMAX); > > +static ktime_t max310x_get_character_duration(const struct ktermios *termios, > + unsigned int baud) > +{ > + const unsigned int startstop = 2; > + const unsigned int char_bits = startstop + > + (((termios->c_cflag & CSIZE) == CS5) ? 5 : 0) + > + (((termios->c_cflag & CSIZE) == CS6) ? 6 : 0) + > + (((termios->c_cflag & CSIZE) == CS7) ? 7 : 0) + > + (((termios->c_cflag & CSIZE) == CS8) ? 8 : 0) + > + ((termios->c_cflag & PARENB) ? 1 : 0) + > + ((termios->c_cflag & CSTOPB) ? 1 : 0); Is this an open-coded tty_get_frame_size()? > + > + return us_to_ktime(DIV_ROUND_UP(USEC_PER_SEC * char_bits, baud)); > +} > + > static u8 max310x_port_read(struct uart_port *port, u8 reg) > { > struct max310x_one *one = to_max310x_port(port); > @@ -680,6 +716,39 @@ static void max310x_batch_read(struct uart_port *port, u8 *rxbuf, unsigned int l > regmap_noinc_read(one->regmap, MAX310X_RHR_REG, rxbuf, len); > } > > +static void max310x_rts_ctl(struct uart_port *port, bool rts_state) > +{ > + max310x_port_update(port, MAX310X_LCR_REG, MAX310X_LCR_RTS_BIT, > + rts_state ? MAX310X_LCR_RTS_BIT : 0); > +} > + > +/* > + * Drive the RS485 RTS line to match the current tx_state. This is the only > + * place that touches RTS, and it reads tx_state rather than a fixed > + * assert/deassert intent, so a newer assert is never clobbered by a stale > + * release. It also arms the before-send timer once the RTS edge is on the wire, > + * so data is never shifted before RTS is asserted. > + */ > +static void max310x_rts_work_proc(struct work_struct *ws) > +{ > + struct max310x_one *one = container_of(ws, struct max310x_one, rts_work); > + struct uart_port *port = &one->port; > + unsigned long flags; > + bool rts_on = READ_ONCE(one->tx_state) != MAX310X_TX_OFF; > + > + max310x_rts_ctl(port, rts_on ? > + (port->rs485.flags & SER_RS485_RTS_ON_SEND) : > + (port->rs485.flags & SER_RS485_RTS_AFTER_SEND)); > + > + spin_lock_irqsave(&port->lock, flags); We use guard()s these days. > + if (READ_ONCE(one->tx_state) == MAX310X_TX_WAIT_BEFORE_SEND && > + !one->cancel_tx_delay_tmr && !hrtimer_active(&one->tx_delay_tmr)) > + hrtimer_start(&one->tx_delay_tmr, > + ms_to_ktime(port->rs485.delay_rts_before_send), > + HRTIMER_MODE_REL); > + spin_unlock_irqrestore(&port->lock, flags); > +} > + > static void max310x_handle_rx(struct uart_port *port, unsigned int rxlen) > { > struct max310x_one *one = to_max310x_port(port); > @@ -776,6 +845,75 @@ static void max310x_handle_rx(struct uart_port *port, unsigned int rxlen) > tty_flip_buffer_push(&port->state->port); > } > > +static enum hrtimer_restart max310x_tmr_tx(struct hrtimer *timer) > +{ > + struct max310x_one *one = container_of(timer, struct max310x_one, > + tx_delay_tmr); > + unsigned long flags; > + > + spin_lock_irqsave(&one->port.lock, flags); guard() on more places. > + if (!one->cancel_tx_delay_tmr) { > + if (READ_ONCE(one->tx_state) == MAX310X_TX_WAIT_AFTER_SEND) { > + /* After-send hold elapsed: drop RTS via the rts worker. */ > + WRITE_ONCE(one->tx_state, MAX310X_TX_OFF); > + schedule_work(&one->rts_work); > + } else { > + WRITE_ONCE(one->tx_state, MAX310X_TX_SEND); > + schedule_work(&one->tx_work); > + } > + } > + spin_unlock_irqrestore(&one->port.lock, flags); > + > + return HRTIMER_NORESTART; > +} thanks, -- js suse labs