From mboxrd@z Thu Jan 1 00:00:00 1970 From: Russell King - ARM Linux Subject: Re: [PATCH v2] ARM: PL011: Add support for Rx DMA buffer polling Date: Fri, 25 Jan 2013 21:26:13 +0000 Message-ID: <20130125212613.GZ23505@n2100.arm.linux.org.uk> References: <50f107aa.894e420a.596a.ffffe3f6SMTPIN_ADDED_BROKEN@mx.google.com> <20130114002608.GV23505@n2100.arm.linux.org.uk> <20130125202507.GB5470@kroah.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from caramon.arm.linux.org.uk ([78.32.30.218]:55511 "EHLO caramon.arm.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752987Ab3AYV0u (ORCPT ); Fri, 25 Jan 2013 16:26:50 -0500 Content-Disposition: inline In-Reply-To: <20130125202507.GB5470@kroah.com> Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Greg Kroah-Hartman Cc: Chanho Min , Linus Walleij , Alan Cox , linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, Pawel Moll On Fri, Jan 25, 2013 at 12:25:07PM -0800, Greg Kroah-Hartman wrote: > On Wed, Jan 23, 2013 at 02:07:57PM +0900, Chanho Min wrote: > > On Tue, Jan 22, 2013 at 10:18 PM, Linus Walleij > > wrote: > > >> - If poll timer is activated, We use consistent DMA mappings to avoid from > > >> the frequent cache operation of the timer function. sg->coherency is used > > >> to check if buffer is coherent. > > > > > > Hm. We can begin like this but maybe we should later patch it to > > > make this the default unless it has performance impacts on our > > > systems. > > Good, I really hope to make this the default. > > We expect it has no impact to system even if no polling use. > > > > > Maybe this is a good opportunity to add some kerneldoc above > > > this struct so as to help platform implementers. It will invariably > > > be reused by Device Tree binding authors later on... > > Agree, but, frankly I need help about what I didn't modify. > > So We will leave this work for the next submit. > > So, should this patch be applied? Can I get an ack from someone who > knows this driver/platform please? Well, I thought I had explained that I'd prefer to see the poll rate adjusted with the baud rate, but maybe I wasn't explicit enough. Instead, what we seem to have ended up with are two new entries in platform data (which we're trying to get away from with DT): + unsigned int dma_rx_poll_rate; + unsigned int dma_rx_poll_timeout; If this were to be done, then receive DMA could be used on the Versatile PB platforms without having it suck CPU usage unnecessarily at slower baud rates.