Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757149AbXITAJJ (ORCPT ); Wed, 19 Sep 2007 20:09:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751482AbXITAI5 (ORCPT ); Wed, 19 Sep 2007 20:08:57 -0400 Received: from mail7.sea5.speakeasy.net ([69.17.117.9]:46798 "EHLO mail7.sea5.speakeasy.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750853AbXITAI5 (ORCPT ); Wed, 19 Sep 2007 20:08:57 -0400 Date: Wed, 19 Sep 2007 17:08:55 -0700 (PDT) From: Trent Piepho X-X-Sender: xyzzy@shell4.speakeasy.net To: Andres Salomon cc: Jonathan Corbet , linux-kernel@vger.kernel.org, v4l-dvb-maintainer@linuxtv.org, video4linux-list@redhat.com, akpm@linux-foundation.org, mchehab@infradead.org Subject: Re: [v4l-dvb-maintainer] [PATCH] cafe_ccic: default to allocating DMA buffers at probe time In-Reply-To: <20070919184338.64fc6e89.dilinger@queued.net> Message-ID: References: <11514.1190230317@lwn.net> <20070919184338.64fc6e89.dilinger@queued.net> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2489 Lines: 49 On Wed, 19 Sep 2007, Andres Salomon wrote: > On Wed, 19 Sep 2007 15:34:42 -0700 (PDT) > Trent Piepho wrote: > > On Wed, 19 Sep 2007, Jonathan Corbet wrote: > > > Andres Salomon wrote: > > > > This patch makes DMA buffer allocation happen during device probe by > > > > default, and changes the parameter to 'alloc_bufs_at_read'. The > > > > camera hardware is there, if the cafe_ccic driver is enabled/loaded it > > > > should do its best to ensure that the camera is actually usable; > > > > delaying DMA buffer allocation saves an insignicant amount of memory, > > > > and causes the driver to be much less useful. > > > > > Changing the parameter name will break the configuration of anyone who was > > using the existing parameter. It also means everyone who has multiple > > We (OLPC) are the only ones using this driver, as we are the only ones with > this hardware. Marvell designed the cafe for us, and it is not available > on the market yet. Backwards compatibility at this point is not a concern. > > > kernels installed and uses this parameter will need to have one > > configuration for old kernels and a different configuration for new > > kernels. > > > > In the default really needs to be changed (what's so hard about setting > > alloc_bufs_at_load in /etc/modprobe{.d,.config}?) then just change the > > default of the existing parameter. That avoids the whole problem with > > different configration files for different module versions. > > We're building the driver in statically; there's no point for us to make > it a module. We could add a kernel argument, yes, but that quickly > becomes unwieldy as we require more and more. We've actually been trying > to cut down the number of kernel args we use. Ok, that seems like a good reason to change the default. > > > That said, I'm not opposed to keeping the parameter name the same while > making the default 1; I just thought that the name 'alloc_bufs_at_read' was > clearer. Another option is to change it to 'no_alloc_bufs_at_load'. Jon, > any preference there? It seems like the name 'alloc_bufs_at_read' isn't quite right, since the buffers will be allocated when the format is set, from cafe_vidioc_s_fmt_cap(). - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/