From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751806AbWFWRZD (ORCPT ); Fri, 23 Jun 2006 13:25:03 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751809AbWFWRZC (ORCPT ); Fri, 23 Jun 2006 13:25:02 -0400 Received: from perninha.conectiva.com.br ([200.140.247.100]:37508 "EHLO perninha.conectiva.com.br") by vger.kernel.org with ESMTP id S1751806AbWFWRZB (ORCPT ); Fri, 23 Jun 2006 13:25:01 -0400 Date: Fri, 23 Jun 2006 14:28:42 -0300 From: "Luiz Fernando N. Capitulino" To: Russell King Cc: Pete Zaitcev , gregkh@suse.de, alan@lxorguk.ukuu.org.uk, linux-kernel@vger.kernel.org, linux-usb-devel@lists.sourceforge.net Subject: Re: Serial-Core: USB-Serial port current issues. Message-ID: <20060623142842.2b35103b@home.brethil> In-Reply-To: <20060622082939.GA25212@flint.arm.linux.org.uk> References: <20060613192829.3f4b7c34@home.brethil> <20060614152809.GA17432@flint.arm.linux.org.uk> <20060620161134.20c1316e@doriath.conectiva> <20060620193233.15224308.zaitcev@redhat.com> <20060621133500.18e82511@doriath.conectiva> <20060621164336.GD24265@flint.arm.linux.org.uk> <20060621181513.235fc23c@doriath.conectiva> <20060622082939.GA25212@flint.arm.linux.org.uk> Organization: Mandriva X-Mailer: Sylpheed-Claws 1.0.4 (GTK+ 1.2.10; x86_64-mandriva-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 22 Jun 2006 09:29:40 +0100 Russell King wrote: | On Wed, Jun 21, 2006 at 06:15:13PM -0300, Luiz Fernando N. Capitulino wrote: | | > | With get_mctrl(), the situation is slightly more complicated, because | > | we need to atomically update tty->hw_stopped in some circumstances | > | (that may also be modified from irq context.) Therefore, to give | > | the driver a consistent locking picture, the spinlock is _always_ | > | held. | > | > Is it too bad (wrong?) to only protect the tty->hw_stopped update | > by the spinlock? Then the call to get_mctrl() could be protected by | > a mutex, or is it messy? | | Consider this scenario with what you're proposing: | | thread irq | | take mutex | get_mctrl | cts changes state | take port lock | mctrl state read | tty->hw_stopped changed state | release port lock | releaes mutex | take port lock | update tty->hw_stopped | release port lock | | Now, tty->hw_stopped does not reflect the hardware state, which will be | buggy and can cause a loss of transmission. | | I'm not sure what to suggest on this one since for USB drivers you do | need to be able to sleep in this method... but for UARTs you must not. Neither do I. :(( I thought we could move the 'tty->hw_stopped' update to a workqueue but it has the same problem you explained above... Greg, any suggestions? -- Luiz Fernando N. Capitulino