From patchwork Wed Jul 13 13:17:22 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: VAMSHI GAJJELA X-Patchwork-Id: 590259 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 9A8FCC433EF for ; Wed, 13 Jul 2022 13:17:34 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235360AbiGMNRe (ORCPT ); Wed, 13 Jul 2022 09:17:34 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40532 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231359AbiGMNRd (ORCPT ); Wed, 13 Jul 2022 09:17:33 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 77D382BC6 for ; Wed, 13 Jul 2022 06:17:29 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id g12-20020a05690203cc00b0066e232409c9so8441169ybs.22 for ; Wed, 13 Jul 2022 06:17:29 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:message-id:mime-version:subject:from:to:cc; bh=oLyFYnPfeBbsdMI1D5MiIAVqtfxKriA/JoWUyBDItRs=; b=kkqCkR0t9of0kYRQg0ELnWvmpY0fNOO85FmPcSftGFP8Uwnkd7hIbc7SW9eMhC5Vr7 lvd7zmUfCBdNduVlDdPse9oPwBPyYPpnpsVM1R7KKskAWNOpO0ZB6mce/Pod2pznbXfO rBQgCe3KNFNGYWQaBCYkQfR1KIYGvCjoZxPX3fuAMbufXmmTLvQ6TiGxWAdSCrtcztll VlaUCqcBOvQpclZ51bfiLUGOHb7UVUYZTk0LwQJwbLwLUjuT90QwqeUI61KZdSr4/fZ5 /aT5ZTOvTFFDZ87q9NlopOAXbXz7pU4zCTTVf6UyeR+RK3VO/lAo7UUWxq75UMVKfWj2 XGcg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:message-id:mime-version:subject:from:to:cc; bh=oLyFYnPfeBbsdMI1D5MiIAVqtfxKriA/JoWUyBDItRs=; b=3WDyfUvMSp/x0k2KB/Z8us/MwIyw4OvAx8/+EmiOLNDvTN/lUxhN7sA5UEKor23k0x 6SNXRMxg2Rm6I4+CdV2QJsslMm9bi7AVftcD3+rzydDdqyMYbOPHkzJOGN2SEkKNJG+h DERkrfOmeabavRuL0gyQx/1UgqITY0ivdLWZcn+wJTdlOqpg7Uh0+AHwEo6aOEps5/OO Fp8++GmrsekPgYejwlA3QWc1E/3oCqJjw15b6OCFs84ANt6htlYHjR9L45vMK5zbnpEb bAAmGFZTkcAAionzizmEyaRihJ0FvjlHK1bqSKOSWlkJTPY4Ezsr1AcXBkoolNv2999x UlZw== X-Gm-Message-State: AJIora/sJmGhDnA+CB1WEdT+yYunt14DcUJkrB55cI26Vs7/E/Qq/kPC L/s0BUanNDIYUAaFSUqDjY/tyohsGTAhPbsGoVRj X-Google-Smtp-Source: AGRyM1tgv/1Rheq4mRhYYatWPvmwK+InGksaBZw6vbnKXvQjSNZAS2qj5vxLQtmRqv9i73lD4UbbloOQSq7bc3g9ROvW X-Received: from vamshig51.c.googlers.com ([fda3:e722:ac3:cc00:3:22c1:c0a8:70c]) (user=vamshigajjela job=sendgmr) by 2002:a81:101:0:b0:314:5477:aae0 with SMTP id 1-20020a810101000000b003145477aae0mr4092131ywb.253.1657718248786; Wed, 13 Jul 2022 06:17:28 -0700 (PDT) Date: Wed, 13 Jul 2022 18:47:22 +0530 Message-Id: <20220713131722.2316829-1-vamshigajjela@google.com> Mime-Version: 1.0 X-Mailer: git-send-email 2.37.0.144.g8ac04bfd2-goog Subject: [PATCH v3] serial: 8250_dw: Avoid pslverr on reading empty receiver fifo From: Vamshi Gajjela To: Andy Shevchenko , Greg Kroah-Hartman , Jiri Slaby Cc: Miquel Raynal , Phil Edworthy , Emil Renner Berthing , Heikki Krogerus , Johan Hovold , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, manugautam@google.com, VAMSHI GAJJELA Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org From: VAMSHI GAJJELA With PSLVERR_RESP_EN parameter set to 1, the device generates an error response when an attempt to read an empty RBR with FIFO enabled. This happens when LCR writes are ignored when UART is busy. dw8250_check_lcr() in retries to update LCR, invokes dw8250_force_idle() to clear and reset FIFO and eventually reads UART_RX causing the error. Avoid this by not reading RBR/UART_RX when no data is available. Signed-off-by: VAMSHI GAJJELA --- v3: - check lsr based on FIFO enablement v2: - update as per review comments (re-format comments, xmas tree ordering) drivers/tty/serial/8250/8250_dw.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c index f57bbd32ef11..7573904579f6 100644 --- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -82,8 +82,21 @@ static inline int dw8250_modify_msr(struct uart_port *p, int offset, int value) static void dw8250_force_idle(struct uart_port *p) { struct uart_8250_port *up = up_to_u8250p(p); + unsigned int lsr; serial8250_clear_and_reinit_fifos(up); + + /* + * With PSLVERR_RESP_EN parameter set to 1, the device generates an + * error response when an attempt to read an empty RBR with FIFO + * enabled. + */ + if (up->fcr & UART_FCR_ENABLE_FIFO) { + lsr = p->serial_in(p, UART_LSR); + if (!(lsr & UART_LSR_DR)) + return; + } + (void)p->serial_in(p, UART_RX); }