From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753429AbaIXHyC (ORCPT ); Wed, 24 Sep 2014 03:54:02 -0400 Received: from www.linutronix.de ([62.245.132.108]:51982 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753372AbaIXHx6 convert rfc822-to-8bit (ORCPT ); Wed, 24 Sep 2014 03:53:58 -0400 Date: Wed, 24 Sep 2014 09:53:46 +0200 From: Sebastian Andrzej Siewior To: Peter Hurley Cc: Frans Klaver , Heikki Krogerus , 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 Subject: Re: [PATCH 09/16] tty: serial: 8250_dma: Add a TX trigger workaround for AM33xx Message-ID: <20140924075346.GB19565@linutronix.de> References: <5411C810.7070906@linutronix.de> <2cf997d9-e7de-465b-915d-3a0a5e7b95f7@email.android.com> <54129F6C.7040508@linutronix.de> <20140912094010.GE28458@ci00147.xsens-tech.local> <5412C21A.8020203@linutronix.de> <20140912102816.GF28458@ci00147.xsens-tech.local> <541716DC.9020904@linutronix.de> <20140917102812.GA20438@ci00147.xsens-tech.local> <20140921204100.GA10111@linutronix.de> <5421A7F7.3070109@hurleysoftware.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8BIT In-Reply-To: <5421A7F7.3070109@hurleysoftware.com> X-Key-Id: 97C4700B X-Key-Fingerprint: 09E2 D1F3 9A3A FF13 C3D3 961C 0688 1C1E 97C4 700B User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Peter Hurley | 2014-09-23 13:03:51 [-0400]: >readline() does this; it 'saves' the caller's termios, sets termios >for non-canonical reads, reads one char, and 'restores' the caller's >termios. interresting, thanks. I guess I would need to opimize this a little so the baudrate isn't going to 0 and back to the requested baudrate. >The tty core calls the driver's wait_until_sent() method before changing >the termios (if TCSADRAIN is used for tcsetattr(), which I think for readline() >it does). The interresting difference is that when I take the yocto RFS and chroot into from Debian then I don't this problem. Not sure if this is really readline or something else… >But DMA is cheating if the UART driver's tx_empty() method is saying the >transmitter is empty while TX DMA is still running. This shouldn't be the case. But I will check this once I able to. After TX-DMA is done, "xmit->tail" is updated and port.icount.tx is incremented. At this time the TX FIFO is still full (up to 64 bytes) and I set UART_IER_THRI to wait until TX FIFO is empty so I can disable runtime-pm. Therefore I would assume LSR does not say BOTH_EMPTY until the FIFO is empty. >Regards, >Peter Hurley Sebastian