From patchwork Wed Jun 17 22:48:11 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Serge Semin X-Patchwork-Id: 11610915 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 EA527912 for ; Wed, 17 Jun 2020 22:49:13 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8BA952080D for ; Wed, 17 Jun 2020 22:49:13 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="LiMfRAXH" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8BA952080D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=baikalelectronics.ru Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:In-Reply-To: Message-ID:Date:Subject:To:From:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=pOOqFliCjP8kBhuAvitFx9PFamUcJZmjk/MmQsOJm6A=; b=LiMfRAXHx+LFna B+vlCUzf3pBcMOP70kcnY90n0GpMFx/huLiSwBy74IJCbGnFtWE3VdZ7uES8D01IS46wWQt3SpSLN dt/gCOXiYFXFW01+w4F6nxaG91vJraES45dWmGTHbKa5zxKeiB6RvTqPi0+lxjyuhhdc1/H9revzC 25BHloF9TXaWOMet2McNcufVcey/ea3YKVyv3Yz0GzMzsVTw5PW2HjSfzldkvWzoBIhMR63T6mRl0 gsGrxzRVm1IGd0/nzCG463IGRs4BhQ3Tmu9DR46Soy/PgNTGJym/RTk23Wt0G/IfEtV8lYiV9YYnJ UoMdC1zz4hvsfWmx9HyA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jlgrg-0007kJ-LQ; Wed, 17 Jun 2020 22:49:04 +0000 Received: from ns2.baikalelectronics.ru ([94.125.187.42] helo=mail.baikalelectronics.ru) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jlgrS-0007YA-S8 for linux-arm-kernel@lists.infradead.org; Wed, 17 Jun 2020 22:48:52 +0000 Received: from localhost (unknown [127.0.0.1]) by mail.baikalelectronics.ru (Postfix) with ESMTP id 834DA80045E4; Wed, 17 Jun 2020 22:48:38 +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 9FpGH8Tr9p4p; Thu, 18 Jun 2020 01:48:35 +0300 (MSK) From: Serge Semin To: Thomas Bogendoerfer , Greg Kroah-Hartman , Jiri Slaby Subject: [PATCH v6 1/3] serial: 8250: Add 8250 port clock update method Date: Thu, 18 Jun 2020 01:48:11 +0300 Message-ID: <20200617224813.23853-2-Sergey.Semin@baikalelectronics.ru> In-Reply-To: <20200617224813.23853-1-Sergey.Semin@baikalelectronics.ru> References: <20200617224813.23853-1-Sergey.Semin@baikalelectronics.ru> MIME-Version: 1.0 X-ClientProxiedBy: MAIL.baikal.int (192.168.51.25) To mail (192.168.51.25) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200617_154851_261786_575222BD X-CRM114-Status: GOOD ( 11.29 ) X-Spam-Score: 0.0 (/) X-Spam-Report: SpamAssassin version 3.4.4 on bombadil.infradead.org summary: Content analysis details: (0.0 points) pts rule name description ---- ---------------------- -------------------------------------------------- 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record -0.0 SPF_PASS SPF: sender matches SPF record X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-kernel@vger.kernel.org, Arnd Bergmann , linux-mips@vger.kernel.org, Russell King , Maxime Ripard , Alexey Malahov , Serge Semin , Serge Semin , linux-serial@vger.kernel.org, Andy Shevchenko , Will Deacon , linux-arm-kernel@lists.infradead.org Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org Some platforms can be designed in a way so the UART port reference clock might be asynchronously changed at some point. In Baikal-T1 SoC this may happen due to the reference clock being shared between two UART ports, on the Allwinner SoC the reference clock is derived from the CPU clock, so any CPU frequency change should get to be known/reflected by/in the UART controller as well. But it's not enough to just update the uart_port->uartclk field of the corresponding UART port, the 8250 controller reference clock divisor should be altered so to preserve current baud rate setting. All of these things is done in a coherent way by calling the serial8250_update_uartclk() method provided in this patch. Though note that it isn't supposed to be called from within the UART port callbacks because the locks using to the protect the UART port data are already taken in there. Signed-off-by: Serge Semin Cc: Alexey Malahov Cc: Thomas Bogendoerfer Cc: Arnd Bergmann Cc: Andy Shevchenko Cc: Maxime Ripard Cc: Will Deacon Cc: Russell King Cc: linux-mips@vger.kernel.org Cc: linux-arm-kernel@lists.infradead.org --- Changelog v4: - Export serial8250_update_uartclk() symbol for GPL modules only. --- drivers/tty/serial/8250/8250_port.c | 38 +++++++++++++++++++++++++++++ include/linux/serial_8250.h | 2 ++ 2 files changed, 40 insertions(+) diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index 4d83c85a7389..5596868c8832 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -2628,6 +2628,44 @@ static unsigned int serial8250_get_baud_rate(struct uart_port *port, (port->uartclk + tolerance) / 16); } +/* + * Note in order to avoid the tty port mutex deadlock don't use the next method + * within the uart port callbacks. Primarily it's supposed to be utilized to + * handle a sudden reference clock rate change. + */ +void serial8250_update_uartclk(struct uart_port *port, unsigned int uartclk) +{ + struct uart_8250_port *up = up_to_u8250p(port); + unsigned int baud, quot, frac = 0; + struct ktermios *termios; + unsigned long flags; + + mutex_lock(&port->state->port.mutex); + + if (port->uartclk == uartclk) + goto out_lock; + + port->uartclk = uartclk; + termios = &port->state->port.tty->termios; + + baud = serial8250_get_baud_rate(port, termios, NULL); + quot = serial8250_get_divisor(port, baud, &frac); + + spin_lock_irqsave(&port->lock, flags); + + uart_update_timeout(port, termios->c_cflag, baud); + + serial8250_set_divisor(port, baud, quot, frac); + serial_port_out(port, UART_LCR, up->lcr); + serial8250_out_MCR(up, UART_MCR_DTR | UART_MCR_RTS); + + spin_unlock_irqrestore(&port->lock, flags); + +out_lock: + mutex_unlock(&port->state->port.mutex); +} +EXPORT_SYMBOL_GPL(serial8250_update_uartclk); + void serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios, struct ktermios *old) diff --git a/include/linux/serial_8250.h b/include/linux/serial_8250.h index 6545f8cfc8fa..2b70f736b091 100644 --- a/include/linux/serial_8250.h +++ b/include/linux/serial_8250.h @@ -155,6 +155,8 @@ extern int early_serial_setup(struct uart_port *port); extern int early_serial8250_setup(struct earlycon_device *device, const char *options); +extern void serial8250_update_uartclk(struct uart_port *port, + unsigned int uartclk); extern void serial8250_do_set_termios(struct uart_port *port, struct ktermios *termios, struct ktermios *old); extern void serial8250_do_set_ldisc(struct uart_port *port,