From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 EA95B18D; Fri, 25 Apr 2025 06:49:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745563741; cv=none; b=HTMfUbsK1FXeaVcHwi1cbCvROZIP4ebNs17u9OBIztQ4XRoCwS2lyifNBwtpJNEhFbiXplxY9g0mRlCYaosQvJVn12jauFriki2tIULoiKYcLxDHNclqZIbZ32HIS6S2bnEw85ULOmtU/ii1dgWmwWQJCv64VFi0XKiHJZNqNz4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745563741; c=relaxed/simple; bh=nJp8JM4fL6QtNcTdsC4q8EJI22PRtigoS547HoWALCg=; h=Message-ID:Date:MIME-Version:Subject:To:References:From: In-Reply-To:Content-Type; b=K4i8dR9V1HzWqxW1v2A4eNEnY/ob4ZWUIlO06oqH+sIaM3cNLh+lNHPstP1+U/0YU/z5QGc+f9Dr9mFonZDmYRWmKPK6XzNQuEa2xjvmDURSyqaFedUSjVxwKYpC8PXtzaQVGMobyfIqNHkTci8M3sClRfdO8Rte8rRuA7Z75uE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=HkPndDs5; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="HkPndDs5" Received: by smtp.kernel.org (Postfix) with ESMTPSA id A5D19C4CEE4; Fri, 25 Apr 2025 06:48:56 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1745563740; bh=nJp8JM4fL6QtNcTdsC4q8EJI22PRtigoS547HoWALCg=; h=Date:Subject:To:References:From:In-Reply-To:From; b=HkPndDs5AJ4n1x88Pn7bhGYHPQq0ceF9gF3LD7g3sjGLtmZIR7y5SpeLDhLyYojPj F0uC3p28Ew75e3bd4XgkV1oLIU3Vh1vqZe22gX+SXL6V8BjrKAkTD06u2CdTxgbBhF MVQMbx7SFbeBLbm1yzhv9nvNyjykbIGin1m+ISD+ututAqxF92kALGWFrAawmcrwjl 1aLT+WYhbXDgAaLIngkt0/gpqUKSI1FAohCBGthD2XQq3Epl0yTeUmdFezHF547YjT chA+pwC3GSh+fwtHEKdDptYNOFz2OruQGHnjDGUh7x1pKLjbi2v/QS6T6mY0QMxvkJ offpn6QczJmvw== Message-ID: <3a24d3ab-9567-4a0c-b904-4225ab4c489b@kernel.org> Date: Fri, 25 Apr 2025 08:48:54 +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 v4 2/4] serial: 8250: introduce serial8250_discard_data() To: Yunhui Cui , arnd@arndb.de, andriy.shevchenko@linux.intel.com, benjamin.larsson@genexis.eu, gregkh@linuxfoundation.org, heikki.krogerus@linux.intel.com, ilpo.jarvinen@linux.intel.com, jkeeping@inmusicbrands.com, john.ogness@linutronix.de, linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, markus.mayer@linaro.org, matt.porter@linaro.org, namcao@linutronix.de, paulmck@kernel.org, pmladek@suse.com, schnelle@linux.ibm.com, sunilvl@ventanamicro.com, tim.kryger@linaro.org References: <20250425062425.68761-1-cuiyunhui@bytedance.com> <20250425062425.68761-2-cuiyunhui@bytedance.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 25. 04. 25, 8:24, Yunhui Cui wrote: > To prevent triggering PSLVERR, it is necessary to check whether the > UART_LSR_DR bit of UART_LSR is set before reading UART_RX. > Ensure atomicity of UART_LSR and UART_RX, put serial8250_discard_data() > under port->lock. > > Signed-off-by: Yunhui Cui > --- > drivers/tty/serial/8250/8250.h | 15 +++++++++++ > drivers/tty/serial/8250/8250_port.c | 42 ++++++++++++++--------------- > 2 files changed, 36 insertions(+), 21 deletions(-) > > diff --git a/drivers/tty/serial/8250/8250.h b/drivers/tty/serial/8250/8250.h > index b861585ca02a..5a106cf88207 100644 > --- a/drivers/tty/serial/8250/8250.h > +++ b/drivers/tty/serial/8250/8250.h > @@ -162,6 +162,21 @@ static inline u16 serial_lsr_in(struct uart_8250_port *up) > return lsr; > } > > +/* > + * To avoid PSLVERR, check UART_LSR_DR in UART_LSR before > + * reading UART_RX. > + */ > +static inline unsigned int serial8250_discard_data(struct uart_8250_port *up) > +{ > + u16 lsr; Is lsr really 16-bit? > + > + lsr = serial_in(up, UART_LSR); > + if (lsr & UART_LSR_DR) > + return serial_in(up, UART_RX); Why does a discard function return a value at all? > + > + return 0; > +} > + > /* > * For the 16C950 > */ > diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c > index a913135d5217..802ac50357c0 100644 > --- a/drivers/tty/serial/8250/8250_port.c > +++ b/drivers/tty/serial/8250/8250_port.c ... > @@ -2137,25 +2136,21 @@ static void wait_for_xmitr(struct uart_8250_port *up, int bits) > static int serial8250_get_poll_char(struct uart_port *port) > { > struct uart_8250_port *up = up_to_u8250p(port); > - int status; > + int status = NO_POLL_CHAR; > u16 lsr; > > serial8250_rpm_get(up); > > + uart_port_lock_irqsave(port, &flags); > lsr = serial_port_in(port, UART_LSR); > - > - if (!(lsr & UART_LSR_DR)) { > - status = NO_POLL_CHAR; > - goto out; > - } > - > - status = serial_port_in(port, UART_RX); > + if ((lsr & UART_LSR_DR)) Too many parentheses. > + status = serial_port_in(port, UART_RX); > + uart_port_unlock_irqrestore(port, flags); thanks, -- js suse labs