From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: Re: [PATCH 3/3] serial: 8250: omap: restore registers on shutdown Date: Thu, 06 Aug 2015 08:27:20 -0400 Message-ID: <55C352A8.3070102@hurleysoftware.com> References: <87egjp2r4a.fsf@linutronix.de> <55BAC67E.1010400@hurleysoftware.com> <20150803160937.GA26497@linutronix.de> <55BF980E.20908@hurleysoftware.com> <55BF9CE0.4080107@linutronix.de> <55BFC1BA.5020605@hurleysoftware.com> <55C0A8F4.4010204@linutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <55C0A8F4.4010204@linutronix.de> Sender: linux-kernel-owner@vger.kernel.org To: Sebastian Andrzej Siewior Cc: John Ogness , linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Tony Lindgren , linux-omap@vger.kernel.org, nsekhar@ti.com, nm@ti.com, linux-serial@vger.kernel.org, Heikki Krogerus List-Id: linux-serial@vger.kernel.org Hi Sebastian, On 08/04/2015 07:58 AM, Sebastian Andrzej Siewior wrote: > On 08/03/2015 09:32 PM, Peter Hurley wrote: > >>> You mean a function in 8250-dma API which does what I did just here >>> with the wait_event() and the wake_up in the callback? That way I could >>> move the termios_wait into the dma struct instead of keeping in the >>> omap specific part. I am also not sure if OMAP is the only one that may >>> hang here or the other people just didn't notice it yet. >> >> Exactly; and we need to fix DMA wrt x_char anyway. >> >> Going back to the dmaengine api, I think something like this might work >> (as a first approximation): >> >> dma_sync_wait(dma->txchan, dma->tx_cookie); >> dmaengine_pause(dma->txchan); >> >> /* remainder of set_termios */ >> >> dmaengine_resume(dma->txchan); >> >> We could require 8250 core dma to support pause/resume. > > I would prefer the waitqueue approach. > You can't do this while holding the port lock. The lock is taken with > irqs off so may not see the transfer completing. > Why do you pause the channel? It may not work without an active > descriptor and a start without "resume" should work. Also you must > ensure that DMA's complete callback does not start another transfer if > there is something queued up (that is why I had the tx_running dance). > I am not sure if a transfer that is active and then paused will not > trigger the hang bug if we change the termios in between. I'll look at/test this this weekend, ok? Regards, Peter Hurley