From mboxrd@z Thu Jan 1 00:00:00 1970 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 58C2EEB64DD for ; Wed, 9 Aug 2023 11:36:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234078AbjHILgf (ORCPT ); Wed, 9 Aug 2023 07:36:35 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51280 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234082AbjHILgf (ORCPT ); Wed, 9 Aug 2023 07:36:35 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D69E51BFA for ; Wed, 9 Aug 2023 04:36:34 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 6EDF563531 for ; Wed, 9 Aug 2023 11:36:34 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7ACC0C433C8; Wed, 9 Aug 2023 11:36:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1691580993; bh=v/YyHskIMONw7W8OYh+x6h1qcGTm1Mgs/t4Mnf22p58=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Id2O4Vv/8cEWRRZPa8ui4zcirbxaxc31DYTfLkq1MySjbIk0NwvXPz8wbcE8d5rf8 R7Pi491jln4RMZ0yGyhtgt68yUIGbjPGnJY2uLn+vwHkDsr+AsslhGi0GlmzXC1I0X yRdceyEkXQ9CNaJ1P/K1m53gbFAALDwxqfnY35OQ= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, stable , Ruihong Luo , =?UTF-8?q?Ilpo=20J=C3=A4rvinen?= , Andy Shevchenko Subject: [PATCH 5.10 068/201] serial: 8250_dw: Preserve original value of DLF register Date: Wed, 9 Aug 2023 12:41:10 +0200 Message-ID: <20230809103646.109426702@linuxfoundation.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230809103643.799166053@linuxfoundation.org> References: <20230809103643.799166053@linuxfoundation.org> User-Agent: quilt/0.67 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Ruihong Luo commit 748c5ea8b8796ae8ee80b8d3a3d940570b588d59 upstream. Preserve the original value of the Divisor Latch Fraction (DLF) register. When the DLF register is modified without preservation, it can disrupt the baudrate settings established by firmware or bootloader, leading to data corruption and the generation of unreadable or distorted characters. Fixes: 701c5e73b296 ("serial: 8250_dw: add fractional divisor support") Cc: stable Signed-off-by: Ruihong Luo Link: https://lore.kernel.org/stable/20230713004235.35904-1-colorsu1922%40gmail.com Reviewed-by: Ilpo Järvinen Reviewed-by: Andy Shevchenko Link: https://lore.kernel.org/r/20230713004235.35904-1-colorsu1922@gmail.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_dwlib.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) --- a/drivers/tty/serial/8250/8250_dwlib.c +++ b/drivers/tty/serial/8250/8250_dwlib.c @@ -80,7 +80,7 @@ static void dw8250_set_divisor(struct ua void dw8250_setup_port(struct uart_port *p) { struct uart_8250_port *up = up_to_u8250p(p); - u32 reg; + u32 reg, old_dlf; /* * If the Component Version Register returns zero, we know that @@ -93,9 +93,11 @@ void dw8250_setup_port(struct uart_port dev_dbg(p->dev, "Designware UART version %c.%c%c\n", (reg >> 24) & 0xff, (reg >> 16) & 0xff, (reg >> 8) & 0xff); + /* Preserve value written by firmware or bootloader */ + old_dlf = dw8250_readl_ext(p, DW_UART_DLF); dw8250_writel_ext(p, DW_UART_DLF, ~0U); reg = dw8250_readl_ext(p, DW_UART_DLF); - dw8250_writel_ext(p, DW_UART_DLF, 0); + dw8250_writel_ext(p, DW_UART_DLF, old_dlf); if (reg) { struct dw8250_port_data *d = p->private_data;