From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5BFB6200A5 for ; Tue, 1 Aug 2023 09:36:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D43E0C433C8; Tue, 1 Aug 2023 09:36:11 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1690882572; bh=l6Pcvzb0AvMm9DsHofV8Ursvkib+BQffG9sT3tfszYQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=U4GAn7wdyvarJz7L251b9dHo+a/xZENPPQ01UjcfFdtRFZ6o0AKSUXZXAwVEL9+OK nXeFKIk8G1RsbJOmJBdhZI73QLOyvUJBHPZiwHU/oOh29MVX3g/y5NSc/C9pSiCaza QNCcYQuxNMe841gVhCSOezlT7NVm4GNVhAn2n+Og= 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 6.1 154/228] serial: 8250_dw: Preserve original value of DLF register Date: Tue, 1 Aug 2023 11:20:12 +0200 Message-ID: <20230801091928.461368035@linuxfoundation.org> X-Mailer: git-send-email 2.41.0 In-Reply-To: <20230801091922.799813980@linuxfoundation.org> References: <20230801091922.799813980@linuxfoundation.org> User-Agent: quilt/0.67 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 @@ -244,7 +244,7 @@ void dw8250_setup_port(struct uart_port struct dw8250_port_data *pd = p->private_data; struct dw8250_data *data = to_dw8250_data(pd); struct uart_8250_port *up = up_to_u8250p(p); - u32 reg; + u32 reg, old_dlf; pd->hw_rs485_support = dw8250_detect_rs485_hw(p); if (pd->hw_rs485_support) { @@ -270,9 +270,11 @@ 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) { pd->dlf_size = fls(reg);