From patchwork Wed Mar 16 14:36:40 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Wander Lairson Costa X-Patchwork-Id: 552502 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 1B3C4C4332F for ; Wed, 16 Mar 2022 14:37:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232943AbiCPOis (ORCPT ); Wed, 16 Mar 2022 10:38:48 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36472 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242188AbiCPOir (ORCPT ); Wed, 16 Mar 2022 10:38:47 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id B09F152E2A for ; Wed, 16 Mar 2022 07:37:33 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647441452; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=46hIDjyKphqtbInFWiNIIVInDMU/QR9kVXm66RmjIvo=; b=TDbaIDviHwFsBV/4Tp89tkhgq/8FDU0+fwGQOLZisVbwL+fSbRYv0MPE5gccuPdMsI5RYI 8Gm3AZZWszptifH3E0kVUNxVkH3n6Pwkv5UIwdTFHKoK0CUbr2PeaHcq4jM51D8IhQxEp+ dHkKwXz37Nc4vGpWs4NhAXS1zhPIofg= Received: from mimecast-mx02.redhat.com (mx3-rdu2.redhat.com [66.187.233.73]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-286-rXzbfaPKNEqOafpE0uKuUw-1; Wed, 16 Mar 2022 10:37:30 -0400 X-MC-Unique: rXzbfaPKNEqOafpE0uKuUw-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id B69F23C23FAA; Wed, 16 Mar 2022 14:37:29 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.19.38]) by smtp.corp.redhat.com (Postfix) with ESMTP id 853F2404D8F1; Wed, 16 Mar 2022 14:37:26 +0000 (UTC) From: Wander Lairson Costa To: Greg Kroah-Hartman , Jiri Slaby , Wander Lairson Costa , Johan Hovold , "Maciej W. Rozycki" , Serge Semin , Lukas Wunner , =?utf-8?q?Pali_Roh=C3=A1r?= , linux-serial@vger.kernel.org (open list:SERIAL DRIVERS), linux-kernel@vger.kernel.org (open list) Cc: rostedt@goodmis.org, senozhatsky@chromium.org, andre.goddard@gmail.com, sudipm.mukherjee@gmail.com, andy.shevchenko@gmail.com, David.Laight@aculab.com, jonathanh@nvidia.com, phil@raspberrypi.com Subject: [PATCH v4 1/5] serial/8250: Use fifo in 8250 console driver Date: Wed, 16 Mar 2022 11:36:40 -0300 Message-Id: <20220316143646.13301-2-wander@redhat.com> In-Reply-To: <20220316143646.13301-1-wander@redhat.com> References: <20220316143646.13301-1-wander@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.11.54.1 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Note: I am using a small test app + driver located at [0] for the problem description. serco is a driver whose write function dispatches to the serial controller. sertest is a user-mode app that writes n bytes to the serial console using the serco driver. While investigating a bug in the RHEL kernel, I noticed that the serial console throughput is way below the configured speed of 115200 bps in a HP Proliant DL380 Gen9. I was expecting something above 10KB/s, but I got 2.5KB/s. $ time ./sertest -n 2500 /tmp/serco real 0m0.997s user 0m0.000s sys 0m0.997s With the help of the function tracer, I then noticed the serial controller was taking around 410us seconds to dispatch one single byte: $ trace-cmd record -p function_graph -g serial8250_console_write \ ./sertest -n 1 /tmp/serco $ trace-cmd report | serial8250_console_write() { 0.384 us | _raw_spin_lock_irqsave(); 1.836 us | io_serial_in(); 1.667 us | io_serial_out(); | uart_console_write() { | serial8250_console_putchar() { | wait_for_xmitr() { 1.870 us | io_serial_in(); 2.238 us | } 1.737 us | io_serial_out(); 4.318 us | } 4.675 us | } | wait_for_xmitr() { 1.635 us | io_serial_in(); | __const_udelay() { 1.125 us | delay_tsc(); 1.429 us | } ... ... ... 1.683 us | io_serial_in(); | __const_udelay() { 1.248 us | delay_tsc(); 1.486 us | } 1.671 us | io_serial_in(); 411.342 us | } In another machine, I measured a throughput of 11.5KB/s, with the serial controller taking between 80-90us to send each byte. That matches the expected throughput for a configuration of 115200 bps. This patch changes the serial8250_console_write to use the 16550 fifo if available. In my benchmarks I got around 25% improvement in the slow machine, and no performance penalty in the fast machine. Signed-off-by: Wander Lairson Costa Link: https://lore.kernel.org/r/20211222112831.1968392-2-wander@redhat.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_port.c | 61 ++++++++++++++++++++++++++--- 1 file changed, 55 insertions(+), 6 deletions(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 3b12bfc1ed67..2abb3de11a48 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2056,10 +2056,7 @@ static void serial8250_break_ctl(struct uart_port *port, int break_state) serial8250_rpm_put(up); } -/* - * Wait for transmitter & holding register to empty - */ -static void wait_for_xmitr(struct uart_8250_port *up, int bits) +static void wait_for_lsr(struct uart_8250_port *up, int bits) { unsigned int status, tmout = 10000; @@ -2076,6 +2073,16 @@ static void wait_for_xmitr(struct uart_8250_port *up, int bits) udelay(1); touch_nmi_watchdog(); } +} + +/* + * Wait for transmitter & holding register to empty + */ +static void wait_for_xmitr(struct uart_8250_port *up, int bits) +{ + unsigned int tmout; + + wait_for_lsr(up, bits); /* Wait up to 1s for flow control if necessary */ if (up->port.flags & UPF_CONS_FLOW) { @@ -3325,6 +3332,35 @@ static void serial8250_console_restore(struct uart_8250_port *up) serial8250_out_MCR(up, UART_MCR_DTR | UART_MCR_RTS); } +/* + * Print a string to the serial port using the device FIFO + * + * It sends fifosize bytes and then waits for the fifo + * to get empty. + */ +static void serial8250_console_fifo_write(struct uart_8250_port *up, + const char *s, unsigned int count) +{ + int i; + const char *end = s + count; + unsigned int fifosize = up->port.fifosize; + bool cr_sent = false; + + while (s != end) { + wait_for_lsr(up, UART_LSR_THRE); + + for (i = 0; i < fifosize && s != end; ++i) { + if (*s == '\n' && !cr_sent) { + serial_out(up, UART_TX, '\r'); + cr_sent = true; + } else { + serial_out(up, UART_TX, *s++); + cr_sent = false; + } + } + } +} + /* * Print a string to the serial port trying not to disturb * any possible real use of the port... @@ -3340,7 +3376,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s, struct uart_8250_em485 *em485 = up->em485; struct uart_port *port = &up->port; unsigned long flags; - unsigned int ier; + unsigned int ier, use_fifo; int locked = 1; touch_nmi_watchdog(); @@ -3372,7 +3408,20 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s, mdelay(port->rs485.delay_rts_before_send); } - uart_console_write(port, s, count, serial8250_console_putchar); + use_fifo = (up->capabilities & UART_CAP_FIFO) && + port->fifosize > 1 && + (serial_port_in(port, UART_FCR) & UART_FCR_ENABLE_FIFO) && + /* + * After we put a data in the fifo, the controller will send + * it regardless of the CTS state. Therefore, only use fifo + * if we don't use control flow. + */ + !(up->port.flags & UPF_CONS_FLOW); + + if (likely(use_fifo)) + serial8250_console_fifo_write(up, s, count); + else + uart_console_write(port, s, count, serial8250_console_putchar); /* * Finally, wait for transmitter to become empty From patchwork Wed Mar 16 14:36:41 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Wander Lairson Costa X-Patchwork-Id: 552128 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 0B58EC433EF for ; Wed, 16 Mar 2022 14:37:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1344173AbiCPOjA (ORCPT ); Wed, 16 Mar 2022 10:39:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:36610 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1344898AbiCPOiy (ORCPT ); Wed, 16 Mar 2022 10:38:54 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 2895B53B5B for ; Wed, 16 Mar 2022 07:37:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647441459; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=cQKY17K5M4BrRuM2rlw2MvxoRzLJI6+f/LllmsWpF+I=; b=ZEEHqOiqj0e5s5Lqwffy04kDtS0d+SZOoHPPeKD5jYQYz2B1KweiEaVSesKqLhMUGMYS56 QMh3gH8a32cOF8QxuzylVh2vodr+UT+dRh62UYODs2fnQsvpCXYAfDt509I03/6VEtmUik T4caCi6ErLa2VkW7MvQOamSZzZLa6MM= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-631-5OMsHSpZOEiI2NivE8y1Rg-1; Wed, 16 Mar 2022 10:37:36 -0400 X-MC-Unique: 5OMsHSpZOEiI2NivE8y1Rg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 277351066558; Wed, 16 Mar 2022 14:37:35 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.19.38]) by smtp.corp.redhat.com (Postfix) with ESMTP id E6895400F73E; Wed, 16 Mar 2022 14:37:31 +0000 (UTC) From: Wander Lairson Costa To: Greg Kroah-Hartman , Jiri Slaby , Johan Hovold , Wander Lairson Costa , "Maciej W. Rozycki" , Serge Semin , Lukas Wunner , =?utf-8?q?Pali_Roh=C3=A1r?= , linux-serial@vger.kernel.org (open list:SERIAL DRIVERS), linux-kernel@vger.kernel.org (open list) Cc: rostedt@goodmis.org, senozhatsky@chromium.org, andre.goddard@gmail.com, sudipm.mukherjee@gmail.com, andy.shevchenko@gmail.com, David.Laight@aculab.com, jonathanh@nvidia.com, phil@raspberrypi.com Subject: [PATCH v4 2/5] serial/8250: Use the cache value of the FCR register Date: Wed, 16 Mar 2022 11:36:41 -0300 Message-Id: <20220316143646.13301-3-wander@redhat.com> In-Reply-To: <20220316143646.13301-1-wander@redhat.com> References: <20220316143646.13301-1-wander@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.11.54.1 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org commit 5021d709b31b ("tty: serial: Use fifo in 8250 console driver") erroneous tries to read the FCR register content, but this register is write-only. This patch fixes that by reading the content from the port struct fcr field. Thanks to Jon Hunter and Jiri Slaby. Suggested-by: Jiri Slaby Reported-by: Jon Hunter Signed-off-by: Wander Lairson Costa --- drivers/tty/serial/8250/8250_port.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 2abb3de11a48..9f3fa9fe2a4e 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -3410,7 +3410,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s, use_fifo = (up->capabilities & UART_CAP_FIFO) && port->fifosize > 1 && - (serial_port_in(port, UART_FCR) & UART_FCR_ENABLE_FIFO) && + (up->fcr & UART_FCR_ENABLE_FIFO) && /* * After we put a data in the fifo, the controller will send * it regardless of the CTS state. Therefore, only use fifo From patchwork Wed Mar 16 14:36:42 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Wander Lairson Costa X-Patchwork-Id: 552501 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 1BF40C433F5 for ; Wed, 16 Mar 2022 14:37:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1345330AbiCPOjI (ORCPT ); Wed, 16 Mar 2022 10:39:08 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37000 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1345781AbiCPOjD (ORCPT ); Wed, 16 Mar 2022 10:39:03 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id CFCA654BE6 for ; Wed, 16 Mar 2022 07:37:45 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647441464; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+puTaoBs7ERRB7dXkYfJVCLixA5oMPMatpnqwUqkD1c=; b=Kr3l8m6MTwAxIts58nvJHPKgKfNQm6Iu5EZRKbhqvcouYhBHE41wr+aPAtl7VmtfsoQZxU aORghj6upIFfw5/u+Jqv76CHeikpcW8sjh9xidf3G82A5HXMfWt4z9zg6iMc3PHGntsxnS K6eGReSj9gdLe0BuKuy7OfFqaUHrZXM= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-358-MY4Rzgv_OJayCNmBJHCkRg-1; Wed, 16 Mar 2022 10:37:41 -0400 X-MC-Unique: MY4Rzgv_OJayCNmBJHCkRg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 68FE8811E83; Wed, 16 Mar 2022 14:37:40 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.19.38]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5B97B400F73E; Wed, 16 Mar 2022 14:37:37 +0000 (UTC) From: Wander Lairson Costa To: Greg Kroah-Hartman , Jiri Slaby , Wander Lairson Costa , Johan Hovold , "Maciej W. Rozycki" , Lukas Wunner , =?utf-8?q?Pali_Roh=C3=A1r?= , linux-serial@vger.kernel.org (open list:SERIAL DRIVERS), linux-kernel@vger.kernel.org (open list) Cc: rostedt@goodmis.org, senozhatsky@chromium.org, andre.goddard@gmail.com, sudipm.mukherjee@gmail.com, andy.shevchenko@gmail.com, David.Laight@aculab.com, jonathanh@nvidia.com, phil@raspberrypi.com Subject: [PATCH v4 3/5] serial/8250: Use tx_loadsz as the transmitter fifo size Date: Wed, 16 Mar 2022 11:36:42 -0300 Message-Id: <20220316143646.13301-4-wander@redhat.com> In-Reply-To: <20220316143646.13301-1-wander@redhat.com> References: <20220316143646.13301-1-wander@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.11.54.1 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org Using port_fifosize as the fifo size to transmit data to the serial console causes data loss in some controllers. Use the correct tx_loadsz field. Thanks to Jon Hunter for reporting the issue. Reported-by: Jon Hunter Tested-by: Jon Hunter Fixes: 5021d709b31b ("tty: serial: Use fifo in 8250 console driver") Signed-off-by: Wander Lairson Costa --- drivers/tty/serial/8250/8250_port.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 9f3fa9fe2a4e..d3a93e5d55f7 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -3343,7 +3343,7 @@ static void serial8250_console_fifo_write(struct uart_8250_port *up, { int i; const char *end = s + count; - unsigned int fifosize = up->port.fifosize; + unsigned int fifosize = up->tx_loadsz; bool cr_sent = false; while (s != end) { @@ -3409,7 +3409,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s, } use_fifo = (up->capabilities & UART_CAP_FIFO) && - port->fifosize > 1 && + up->tx_loadsz > 1 && (up->fcr & UART_FCR_ENABLE_FIFO) && /* * After we put a data in the fifo, the controller will send From patchwork Wed Mar 16 14:36:44 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Wander Lairson Costa X-Patchwork-Id: 552500 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 829FAC433EF for ; Wed, 16 Mar 2022 14:38:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1348341AbiCPOjN (ORCPT ); Wed, 16 Mar 2022 10:39:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37362 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1356549AbiCPOjK (ORCPT ); Wed, 16 Mar 2022 10:39:10 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id B27C8326 for ; Wed, 16 Mar 2022 07:37:56 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1647441475; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=FdaRFj6Txp5dVh+5ToS7luAujkKT+3c923Qns25TpZk=; b=eF9HrZBMUMOCjz+Bgb7263C8DaJlcYicUn09+viv6d/yvstNHxlkTzgR3lkvMdWhw6fEqL /9rzwhql0c7XJDhRhM4Oc/F/9MaEdKyRg1DS/FHeGdSZSaPJvo4FgyYaMareXdb4wZD4fV J0piltlXplrvu6HgSe/z9qtAdQEDJf0= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-520-PX3TcyXXMn21kXKpX9Klgg-1; Wed, 16 Mar 2022 10:37:52 -0400 X-MC-Unique: PX3TcyXXMn21kXKpX9Klgg-1 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.rdu2.redhat.com [10.11.54.1]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 453D91801388; Wed, 16 Mar 2022 14:37:51 +0000 (UTC) Received: from fedora.redhat.com (unknown [10.22.19.38]) by smtp.corp.redhat.com (Postfix) with ESMTP id 132C1400F73E; Wed, 16 Mar 2022 14:37:47 +0000 (UTC) From: Wander Lairson Costa To: Greg Kroah-Hartman , Jiri Slaby , Johan Hovold , Wander Lairson Costa , "Maciej W. Rozycki" , Serge Semin , Lukas Wunner , =?utf-8?q?Pali_Roh=C3=A1r?= , linux-serial@vger.kernel.org (open list:SERIAL DRIVERS), linux-kernel@vger.kernel.org (open list) Cc: rostedt@goodmis.org, senozhatsky@chromium.org, andre.goddard@gmail.com, sudipm.mukherjee@gmail.com, andy.shevchenko@gmail.com, David.Laight@aculab.com, jonathanh@nvidia.com, phil@raspberrypi.com Subject: [PATCH v4 5/5] serial/8250: Only use fifo after the port is initialized in console_write Date: Wed, 16 Mar 2022 11:36:44 -0300 Message-Id: <20220316143646.13301-6-wander@redhat.com> In-Reply-To: <20220316143646.13301-1-wander@redhat.com> References: <20220316143646.13301-1-wander@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.11.54.1 Precedence: bulk List-ID: X-Mailing-List: linux-serial@vger.kernel.org The serial driver set the value of uart_8250_port.fcr in the function serial8250_config_port, but only writes the value to the controller register later in the initalization code. That opens a small window in which is not safe to use the fifo for console write. Make sure the port is initialized correctly before reading the FCR cached value. Unfortunately, I lost track of who originally reported the issue. If s/he is reading this, please speak up so I can give you the due credit. Signed-off-by: Wander Lairson Costa --- drivers/tty/serial/8250/8250_port.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 4acf620be241..7e2227161555 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -3416,6 +3416,7 @@ void serial8250_console_write(struct uart_8250_port *up, const char *s, !(up->capabilities & UART_CAP_MINI) && up->tx_loadsz > 1 && (up->fcr & UART_FCR_ENABLE_FIFO) && + test_bit(TTY_PORT_INITIALIZED, &port->state->port.iflags) && /* * After we put a data in the fifo, the controller will send * it regardless of the CTS state. Therefore, only use fifo