From patchwork Wed May 6 23:31:32 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Serge Semin X-Patchwork-Id: 11532029 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 2C36C15E6 for ; Wed, 6 May 2020 23:32:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0F7CF208CA for ; Wed, 6 May 2020 23:32:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727852AbgEFXbz (ORCPT ); Wed, 6 May 2020 19:31:55 -0400 Received: from mail.baikalelectronics.com ([87.245.175.226]:34558 "EHLO mail.baikalelectronics.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727119AbgEFXby (ORCPT ); Wed, 6 May 2020 19:31:54 -0400 Received: from localhost (unknown [127.0.0.1]) by mail.baikalelectronics.ru (Postfix) with ESMTP id 70B2C8030808; Wed, 6 May 2020 23:31:51 +0000 (UTC) X-Virus-Scanned: amavisd-new at baikalelectronics.ru Received: from mail.baikalelectronics.ru ([127.0.0.1]) by localhost (mail.baikalelectronics.ru [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id MhBbxmp3w3vz; Thu, 7 May 2020 02:31:48 +0300 (MSK) From: Serge Semin To: Thomas Bogendoerfer , Greg Kroah-Hartman , Jiri Slaby , Long Cheng CC: Serge Semin , Serge Semin , Alexey Malahov , Paul Burton , Ralf Baechle , Arnd Bergmann , Andy Shevchenko , Maxime Ripard , Catalin Marinas , Will Deacon , Russell King , , , , Lukas Wunner , Mika Westerberg , Stefan Roese , Vignesh Raghavendra , , Subject: [PATCH v3 1/4] serial: 8250: Fix max baud limit in generic 8250 port Date: Thu, 7 May 2020 02:31:32 +0300 Message-ID: <20200506233136.11842-2-Sergey.Semin@baikalelectronics.ru> In-Reply-To: <20200506233136.11842-1-Sergey.Semin@baikalelectronics.ru> References: <20200323024611.16039-1-Sergey.Semin@baikalelectronics.ru> <20200506233136.11842-1-Sergey.Semin@baikalelectronics.ru> MIME-Version: 1.0 X-ClientProxiedBy: MAIL.baikal.int (192.168.51.25) To mail (192.168.51.25) Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org Standard 8250 UART ports are designed in a way so they can communicate with baud rates up to 1/16 of a reference frequency. It's expected from most of the currently supported UART controllers. That's why the former version of serial8250_get_baud_rate() method called uart_get_baud_rate() with min and max baud rates passed as (port->uartclk / 16 / UART_DIV_MAX) and ((port->uartclk + tolerance) / 16) respectively. Doing otherwise, like it was suggested in commit ("serial: 8250_mtk: support big baud rate."), caused acceptance of bauds, which was higher than the normal UART controllers actually supported. As a result if some user-space program requested to set a baud greater than (uartclk / 16) it would have been permitted without truncation, but then serial8250_get_divisor(baud) (which calls uart_get_divisor() to get the reference clock divisor) would have returned a zero divisor. Setting zero divisor will cause an unpredictable effect varying from chip to chip. In case of DW APB UART the communications just stop. Lets fix this problem by getting back the limitation of (uartclk + tolerance) / 16 maximum baud supported by the generic 8250 port. Mediatek 8250 UART ports driver developer shouldn't have touched it in the first place notably seeing he already provided a custom version of set_termios() callback in that glue-driver which took into account the extended baud rate values and accordingly updated the standard and vendor-specific divisor latch registers anyway. Fixes: 81bb549fdf14 ("serial: 8250_mtk: support big baud rate.") Signed-off-by: Serge Semin Cc: Alexey Malahov Cc: Thomas Bogendoerfer Cc: Paul Burton Cc: Ralf Baechle Cc: Arnd Bergmann Cc: Long Cheng Cc: Andy Shevchenko Cc: Maxime Ripard Cc: Catalin Marinas Cc: Will Deacon Cc: Russell King Cc: linux-mips@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-mediatek@lists.infradead.org Reviewed-by: Andy Shevchenko --- drivers/tty/serial/8250/8250_port.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index f77bf820b7a3..4d83c85a7389 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2615,6 +2615,8 @@ static unsigned int serial8250_get_baud_rate(struct uart_port *port, struct ktermios *termios, struct ktermios *old) { + unsigned int tolerance = port->uartclk / 100; + /* * Ask the core to calculate the divisor for us. * Allow 1% tolerance at the upper limit so uart clks marginally @@ -2623,7 +2625,7 @@ static unsigned int serial8250_get_baud_rate(struct uart_port *port, */ return uart_get_baud_rate(port, termios, old, port->uartclk / 16 / UART_DIV_MAX, - port->uartclk); + (port->uartclk + tolerance) / 16); } void