From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161051AbaDPTAB (ORCPT ); Wed, 16 Apr 2014 15:00:01 -0400 Received: from mail-lb0-f174.google.com ([209.85.217.174]:43915 "EHLO mail-lb0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756446AbaDPS74 (ORCPT ); Wed, 16 Apr 2014 14:59:56 -0400 User-Agent: K-9 Mail for Android In-Reply-To: <20140416193532.0782f045@alan.etchedpixels.co.uk> References: <1397668411-27162-7-git-send-email-ynvich@gmail.com> <1397668667-27328-1-git-send-email-ynvich@gmail.com> <1397668667-27328-6-git-send-email-ynvich@gmail.com> <20140416193532.0782f045@alan.etchedpixels.co.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Subject: Re: [PATCH v4 12/21] serial: support for 16550A serial ports on LP-8x4x From: Sergei Ianovich Date: Wed, 16 Apr 2014 23:01:47 +0400 To: One Thousand Gnomes CC: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Randy Dunlap , Russell King , Greg Kroah-Hartman , Jiri Slaby , Grant Likely , Heikki Krogerus , Arnd Bergmann , Paul Bolle , Stefan Seyfried , James Cameron , devicetree@vger.kernel.org, linux-doc@vger.kernel.org, linux-serial@vger.kernel.org Message-ID: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org One Thousand Gnomes wrote: >> + baud = uart_get_baud_rate(port, termios, old, >> + port->uartclk / 16 / 0xffff, >> + port->uartclk / 16); >> + switch (baud) { >> + case 2400: >> + len |= 1; >> + break; >> + case 4800: >> + len |= 2; >> + break; >> + case 19200: >> + len |= 4; >> + break; >> + case 38400: >> + len |= 5; >> + break; >> + case 57600: >> + len |= 6; >> + break; >> + case 115200: >> + len |= 7; >> + break; >> + case 9600: >> + default: >> + len |= 3; >> + break; >> + }; > >Some explanation of this would be useful - eg why is it set to 7 for >115200 baud and 3 for 115201 baud ? I am not related to the device vendor in any way, so please take my answers for what they are worth. It seems that there is not enough pins to properly connect the chips to the memory bus and just you the standard 8250 UART driver. Instead, clock divisor is set using this register. So, if you know you're asking for (115200) you get it. If you don't or guess (115201), you get the default 9600. This is a policy, it may not be the right way to write a driver, but it is cheap and it works. From mboxrd@z Thu Jan 1 00:00:00 1970 From: ynvich@gmail.com (Sergei Ianovich) Date: Wed, 16 Apr 2014 23:01:47 +0400 Subject: [PATCH v4 12/21] serial: support for 16550A serial ports on LP-8x4x In-Reply-To: <20140416193532.0782f045@alan.etchedpixels.co.uk> References: <1397668411-27162-7-git-send-email-ynvich@gmail.com> <1397668667-27328-1-git-send-email-ynvich@gmail.com> <1397668667-27328-6-git-send-email-ynvich@gmail.com> <20140416193532.0782f045@alan.etchedpixels.co.uk> Message-ID: To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org One Thousand Gnomes wrote: >> + baud = uart_get_baud_rate(port, termios, old, >> + port->uartclk / 16 / 0xffff, >> + port->uartclk / 16); >> + switch (baud) { >> + case 2400: >> + len |= 1; >> + break; >> + case 4800: >> + len |= 2; >> + break; >> + case 19200: >> + len |= 4; >> + break; >> + case 38400: >> + len |= 5; >> + break; >> + case 57600: >> + len |= 6; >> + break; >> + case 115200: >> + len |= 7; >> + break; >> + case 9600: >> + default: >> + len |= 3; >> + break; >> + }; > >Some explanation of this would be useful - eg why is it set to 7 for >115200 baud and 3 for 115201 baud ? I am not related to the device vendor in any way, so please take my answers for what they are worth. It seems that there is not enough pins to properly connect the chips to the memory bus and just you the standard 8250 UART driver. Instead, clock divisor is set using this register. So, if you know you're asking for (115200) you get it. If you don't or guess (115201), you get the default 9600. This is a policy, it may not be the right way to write a driver, but it is cheap and it works.