From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932178AbbBLJkm (ORCPT ); Thu, 12 Feb 2015 04:40:42 -0500 Received: from pandora.arm.linux.org.uk ([78.32.30.218]:36142 "EHLO pandora.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755293AbbBLJki (ORCPT ); Thu, 12 Feb 2015 04:40:38 -0500 Date: Thu, 12 Feb 2015 09:40:20 +0000 From: Russell King - ARM Linux To: Sebastian Andrzej Siewior Cc: Peter Hurley , Tony Lindgren , Nicolas Schichan , gregkh@linuxfoundation.org, linux-kernel@vger.kernel.org, balbi@ti.com, linux-serial@vger.kernel.org, linux-omap@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH 03/16] tty: serial: 8250_core: read only RX if there is something in the FIFO Message-ID: <20150212094020.GE8670@n2100.arm.linux.org.uk> References: <1410377411-26656-1-git-send-email-bigeasy@linutronix.de> <1410377411-26656-4-git-send-email-bigeasy@linutronix.de> <54D8B772.1010405@freebox.fr> <54D9441B.7070403@hurleysoftware.com> <54D9F3C7.5000809@freebox.fr> <54DA43F8.9090904@hurleysoftware.com> <54DBB531.2030504@hurleysoftware.com> <20150211200313.GE2531@atomide.com> <54DBBE9E.90104@hurleysoftware.com> <54DC6832.3070507@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <54DC6832.3070507@linutronix.de> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Feb 12, 2015 at 09:45:38AM +0100, Sebastian Andrzej Siewior wrote: > On 02/11/2015 09:42 PM, Peter Hurley wrote: > > >> Reverting makes sense to me if it has caused a regression. Maybe Sebastian > >> can update his patch to do this based on some quirk flag instead? > > > > That's fine with me. There's a 'bugs' field in struct 8250_uart_port and > > UART_BUG_* defines in 8250/8250.h for that purpose. > > Makes sense. Reading an empty FIFO does not look right. Maybe we should > do the bug flag the other way around? But I can do what I am told to so > if there is more fallout than just this Marvell UART I could come > around with a patch to the bug field for the older OMAP. Reading the RX FIFO is something that goes back a long time in the 8250 driver, to the time when Ted Ts'o wrote the driver. I would suggest that it remains there as the default (it was obviously found to be necessary for x86 all those years ago when Linux was in its infancy) and has survived for getting on 20 years without issue. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net. From mboxrd@z Thu Jan 1 00:00:00 1970 From: linux@arm.linux.org.uk (Russell King - ARM Linux) Date: Thu, 12 Feb 2015 09:40:20 +0000 Subject: [PATCH 03/16] tty: serial: 8250_core: read only RX if there is something in the FIFO In-Reply-To: <54DC6832.3070507@linutronix.de> References: <1410377411-26656-1-git-send-email-bigeasy@linutronix.de> <1410377411-26656-4-git-send-email-bigeasy@linutronix.de> <54D8B772.1010405@freebox.fr> <54D9441B.7070403@hurleysoftware.com> <54D9F3C7.5000809@freebox.fr> <54DA43F8.9090904@hurleysoftware.com> <54DBB531.2030504@hurleysoftware.com> <20150211200313.GE2531@atomide.com> <54DBBE9E.90104@hurleysoftware.com> <54DC6832.3070507@linutronix.de> Message-ID: <20150212094020.GE8670@n2100.arm.linux.org.uk> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, Feb 12, 2015 at 09:45:38AM +0100, Sebastian Andrzej Siewior wrote: > On 02/11/2015 09:42 PM, Peter Hurley wrote: > > >> Reverting makes sense to me if it has caused a regression. Maybe Sebastian > >> can update his patch to do this based on some quirk flag instead? > > > > That's fine with me. There's a 'bugs' field in struct 8250_uart_port and > > UART_BUG_* defines in 8250/8250.h for that purpose. > > Makes sense. Reading an empty FIFO does not look right. Maybe we should > do the bug flag the other way around? But I can do what I am told to so > if there is more fallout than just this Marvell UART I could come > around with a patch to the bug field for the older OMAP. Reading the RX FIFO is something that goes back a long time in the 8250 driver, to the time when Ted Ts'o wrote the driver. I would suggest that it remains there as the default (it was obviously found to be necessary for x86 all those years ago when Linux was in its infancy) and has survived for getting on 20 years without issue. -- FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up according to speedtest.net.