From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sebastian Andrzej Siewior Subject: Re: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx Date: Fri, 12 Sep 2014 09:23:24 +0200 Message-ID: <54129F6C.7040508@linutronix.de> References: <1410377411-26656-1-git-send-email-bigeasy@linutronix.de> <1410377411-26656-10-git-send-email-bigeasy@linutronix.de> <20140911111721.GB17476@xps8300> <54118AAB.2010205@linutronix.de> <5411967A.6090406@hurleysoftware.com> <54119AAA.9080907@linutronix.de> <20140911151114.GD28458@ci00147.xsens-tech.local> <5411C810.7070906@linutronix.de> <2cf997d9-e7de-465b-915d-3a0a5e7b95f7@email.android.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: Received: from www.linutronix.de ([62.245.132.108]:45669 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752436AbaILHXa (ORCPT ); Fri, 12 Sep 2014 03:23:30 -0400 In-Reply-To: <2cf997d9-e7de-465b-915d-3a0a5e7b95f7@email.android.com> Sender: linux-omap-owner@vger.kernel.org List-Id: linux-omap@vger.kernel.org To: Frans Klaver , Frans Klaver Cc: Heikki Krogerus , Peter Hurley , tony@atomide.com, 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, Alan Cox On 09/11/2014 07:04 PM, Frans Klaver wrote: > On 11 September 2014 18:04:32 CEST, Sebastian Andrzej Siewior wrote: >> On 09/11/2014 05:11 PM, Frans Klaver wrote: >> >>> I can still reproduce it on am335x. I can get out of it as soon as >>> something else gets written to the console though. >>> >>> # echo "<3>something" >/dev/kmsg >> >> Is this to stall it or to get out of it? > > This is to get out of it. I do this from an ssh connection after the console got stuck. The 3 kind of ensures the message is actually sent to ttyS0. Interesting. This shouldn't do anything. If there is a TX operation in progress then ->start_tx() will simply return and the xmit buffer will be send once the current TX operation completes. Is there anything I can do to reproduce this behavior? This problem only pops-up if you use DMA. With disabled DMA you don't see this, right? Sebastian From mboxrd@z Thu Jan 1 00:00:00 1970 From: bigeasy@linutronix.de (Sebastian Andrzej Siewior) Date: Fri, 12 Sep 2014 09:23:24 +0200 Subject: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx In-Reply-To: <2cf997d9-e7de-465b-915d-3a0a5e7b95f7@email.android.com> References: <1410377411-26656-1-git-send-email-bigeasy@linutronix.de> <1410377411-26656-10-git-send-email-bigeasy@linutronix.de> <20140911111721.GB17476@xps8300> <54118AAB.2010205@linutronix.de> <5411967A.6090406@hurleysoftware.com> <54119AAA.9080907@linutronix.de> <20140911151114.GD28458@ci00147.xsens-tech.local> <5411C810.7070906@linutronix.de> <2cf997d9-e7de-465b-915d-3a0a5e7b95f7@email.android.com> Message-ID: <54129F6C.7040508@linutronix.de> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 09/11/2014 07:04 PM, Frans Klaver wrote: > On 11 September 2014 18:04:32 CEST, Sebastian Andrzej Siewior wrote: >> On 09/11/2014 05:11 PM, Frans Klaver wrote: >> >>> I can still reproduce it on am335x. I can get out of it as soon as >>> something else gets written to the console though. >>> >>> # echo "<3>something" >/dev/kmsg >> >> Is this to stall it or to get out of it? > > This is to get out of it. I do this from an ssh connection after the console got stuck. The 3 kind of ensures the message is actually sent to ttyS0. Interesting. This shouldn't do anything. If there is a TX operation in progress then ->start_tx() will simply return and the xmit buffer will be send once the current TX operation completes. Is there anything I can do to reproduce this behavior? This problem only pops-up if you use DMA. With disabled DMA you don't see this, right? Sebastian