From nobody Tue Dec 30 16:38:16 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7438EC4332F for ; Tue, 14 Nov 2023 07:58:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232246AbjKNH6h (ORCPT ); Tue, 14 Nov 2023 02:58:37 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53024 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229566AbjKNH6f (ORCPT ); Tue, 14 Nov 2023 02:58:35 -0500 X-Greylist: delayed 554 seconds by postgrey-1.37 at lindbergh.monkeyblade.net; Mon, 13 Nov 2023 23:58:31 PST Received: from mail.bugwerft.de (mail.bugwerft.de [46.23.86.59]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id BC86619B; Mon, 13 Nov 2023 23:58:31 -0800 (PST) Received: from hq-00595.fritz.box (unknown [178.19.214.146]) by mail.bugwerft.de (Postfix) with ESMTPSA id 05DF928071D; Tue, 14 Nov 2023 07:49:15 +0000 (UTC) From: Daniel Mack To: gregkh@linuxfoundation.org, jirislaby@kernel.org, lech.perczak@camlingroup.com, u.kleine-koenig@pengutronix.de Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, Daniel Mack , Maxim Popov , stable@vger.kernel.org Subject: [PATCH] serial: sc16is7xx: address RX timeout interrupt errata Date: Tue, 14 Nov 2023 08:49:04 +0100 Message-ID: <20231114074904.239458-1-daniel@zonque.org> X-Mailer: git-send-email 2.41.0 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Type: text/plain; charset="utf-8" This devices has a silicon bug that makes it report a timeout interrupt but no data in FIFO. The datasheet states the following in the errata section 18.1.4: "If the host reads the receive FIFO at the at the same time as a time-out interrupt condition happens, the host might read 0xCC (time-out) in the Interrupt Indication Register (IIR), but bit 0 of the Line Status Register (LSR) is not set (means there is not data in the receive FIFO)." When this happens, the loop in sc16is7xx_irq() will run forever, which effectively blocks the i2c bus and breaks the functionality of the UART. From the information above, it is assumed that when the bug is triggered, the FIFO does in fact have payload in its buffer, but the fill level reporting is off-by-one. Hence this patch fixes the issue by reading one byte from the FIFO when that condition is detected. This clears the interrupt and hence breaks the polling loop. Signed-off-by: Daniel Mack Co-Developed-by: Maxim Popov Cc: stable@vger.kernel.org --- drivers/tty/serial/sc16is7xx.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c index 289ca7d4e566..76f76e510ed1 100644 --- a/drivers/tty/serial/sc16is7xx.c +++ b/drivers/tty/serial/sc16is7xx.c @@ -765,6 +765,18 @@ static bool sc16is7xx_port_irq(struct sc16is7xx_port *= s, int portno) case SC16IS7XX_IIR_RTOI_SRC: case SC16IS7XX_IIR_XOFFI_SRC: rxlen =3D sc16is7xx_port_read(port, SC16IS7XX_RXLVL_REG); + + /* + * There is a silicon bug that makes the chip report a + * time-out interrupt but no data in the FIFO. This is + * described in errata section 18.1.4. + * + * When this happens, read one byte from the FIFO to + * clear the interrupt. + */ + if (iir =3D=3D SC16IS7XX_IIR_RTOI_SRC && !rxlen) + rxlen =3D 1; + if (rxlen) sc16is7xx_handle_rx(port, rxlen, iir); break; --=20 2.41.0