From patchwork Tue Sep 29 10:58:35 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 291124 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-13.5 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED, DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH, MAILING_LIST_MULTI, SIGNED_OFF_BY, SPF_HELO_NONE, SPF_PASS, URIBL_BLOCKED, USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 6C945C4727C for ; Tue, 29 Sep 2020 11:39:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 24D2F208B8 for ; Tue, 29 Sep 2020 11:39:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601379587; bh=siXwj0rYJfM0A6UG/dYuL14jfRWRzsXpgV4XZWY0O6g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=sywtsvH5yZ+VckTURtHbyEcGv5WxihBj8gUQJsFXAF6ysuaTjojMoUY1oWfNNtOPN fYVev778lasTzQPcnETZvJcHzqZMH1RIByYpvO1gHEiRuh14V2VGpnSq32naVss9q8 DrcezVf2pkv5Oi8iMukWbIs0foXEiEJZ/WLxtj0k= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730263AbgI2Ljq (ORCPT ); Tue, 29 Sep 2020 07:39:46 -0400 Received: from mail.kernel.org ([198.145.29.99]:34382 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729983AbgI2Ljf (ORCPT ); Tue, 29 Sep 2020 07:39:35 -0400 Received: from localhost (83-86-74-64.cable.dynamic.v4.ziggo.nl [83.86.74.64]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E1DCD21D7F; Tue, 29 Sep 2020 11:39:31 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601379572; bh=siXwj0rYJfM0A6UG/dYuL14jfRWRzsXpgV4XZWY0O6g=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=UV2bR9FtPJ7bgnfce5bGKgEjAqJp0915Xx61wAvPSJx5bsdF3rOBlgPdj3wZtGadU dI2J70+7dGP0/15XsADv693nv9x0qhgYOL3SUiMZyNMZ4sqCkNQMX1RWRrfLp313cE 9Ne5yeE2FhFRj0m9yrVo/v/JP+cmYlkrFu+GUoyw= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Vignesh Raghavendra , Sasha Levin Subject: [PATCH 5.4 184/388] serial: 8250_port: Dont service RX FIFO if throttled Date: Tue, 29 Sep 2020 12:58:35 +0200 Message-Id: <20200929110019.385713326@linuxfoundation.org> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200929110010.467764689@linuxfoundation.org> References: <20200929110010.467764689@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Vignesh Raghavendra [ Upstream commit f19c3f6c8109b8bab000afd35580929958e087a9 ] When port's throttle callback is called, it should stop pushing any more data into TTY buffer to avoid buffer overflow. This means driver has to stop HW from receiving more data and assert the HW flow control. For UARTs with auto HW flow control (such as 8250_omap) manual assertion of flow control line is not possible and only way is to allow RX FIFO to fill up, thus trigger auto HW flow control logic. Therefore make sure that 8250 generic IRQ handler does not drain data when port is stopped (i.e UART_LSR_DR is unset in read_status_mask). Not servicing, RX FIFO would trigger auto HW flow control when FIFO occupancy reaches preset threshold, thus halting RX. Since, error conditions in UART_LSR register are cleared just by reading the register, data has to be drained in case there are FIFO errors, else error information will lost. Signed-off-by: Vignesh Raghavendra Link: https://lore.kernel.org/r/20200319103230.16867-2-vigneshr@ti.com Signed-off-by: Greg Kroah-Hartman Signed-off-by: Sasha Levin --- drivers/tty/serial/8250/8250_port.c | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 90f09ed6e5ad3..5b673077639ba 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1816,6 +1816,7 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir) unsigned char status; unsigned long flags; struct uart_8250_port *up = up_to_u8250p(port); + bool skip_rx = false; if (iir & UART_IIR_NO_INT) return 0; @@ -1824,7 +1825,20 @@ int serial8250_handle_irq(struct uart_port *port, unsigned int iir) status = serial_port_in(port, UART_LSR); - if (status & (UART_LSR_DR | UART_LSR_BI)) { + /* + * If port is stopped and there are no error conditions in the + * FIFO, then don't drain the FIFO, as this may lead to TTY buffer + * overflow. Not servicing, RX FIFO would trigger auto HW flow + * control when FIFO occupancy reaches preset threshold, thus + * halting RX. This only works when auto HW flow control is + * available. + */ + if (!(status & (UART_LSR_FIFOE | UART_LSR_BRK_ERROR_BITS)) && + (port->status & (UPSTAT_AUTOCTS | UPSTAT_AUTORTS)) && + !(port->read_status_mask & UART_LSR_DR)) + skip_rx = true; + + if (status & (UART_LSR_DR | UART_LSR_BI) && !skip_rx) { if (!up->dma || handle_rx_dma(up, iir)) status = serial8250_rx_chars(up, status); }