From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752141AbcAVKHg (ORCPT ); Fri, 22 Jan 2016 05:07:36 -0500 Received: from queue01c.mail.zen.net.uk ([212.23.3.237]:49691 "EHLO queue01c.mail.zen.net.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751645AbcAVKHa (ORCPT ); Fri, 22 Jan 2016 05:07:30 -0500 X-Greylist: delayed 1437 seconds by postgrey-1.27 at vger.kernel.org; Fri, 22 Jan 2016 05:07:29 EST Message-ID: <1453455803.2848.9.camel@linaro.org> Subject: Re: [PATCH] staging: android: ion: Set the length of the DMA sg entries in buffer From: "Jon Medhurst (Tixy)" To: Laura Abbott Cc: Greg Kroah-Hartman , Arve =?ISO-8859-1?Q?Hj=F8nnev=E5g?= , Riley Andrews , Liviu Dudau , devel@driverdev.osuosl.org, linux-kernel@vger.kernel.org, Robin Murphy Date: Fri, 22 Jan 2016 09:43:23 +0000 In-Reply-To: <56A17ED3.80105@redhat.com> References: <1453377467.2858.14.camel@linaro.org> <56A117B6.7050503@redhat.com> <1453407559.2858.77.camel@linaro.org> <56A17ED3.80105@redhat.com> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.12.9-1+b1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit X-Originating-smarthost01a-IP: [82.69.122.217] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2016-01-21 at 16:58 -0800, Laura Abbott wrote: > On 01/21/2016 12:19 PM, Jon Medhurst (Tixy) wrote: [...] > > If sg_dma_len() is correct or acceptable then it seems to me that the > > ION code should set that length. Especially as the comment in the code > > implies it's faking a call to map_sg and grepping the kernel tree for > > real implementations of that functionality seems to show the dma_address > > getting set. > > > > As you can probably tell, I feel I may be on shaky ground. This is > > because I don't fully understanding the code and suspecting both the ION > > and GPU code is rather dodgy (and possibly the bits in between :-) > > > > I blame the Ion code completely. I remember hitting a similar problem > with other out of tree drivers. The solution then was to have drivers > switch to using sg->length instead of sg_dma_len given the state of that > tree. For the Mali driver, if it is ever going to be backed by an IOMMU > you will need to use sg_dma_len so I think at least that part of your > code is correct. > > Thinking about it some, I'm okay with the patch going in. I thought > there was some reason why the out of tree code from before didn't just > do this hack but I can't remember it. It may have been an out of tree > use case. This does go well with Ion's behavior of pretending to do > DMA mapping. More out of tree users can plead their case if it breaks. Well, the $subject patch is copying the value of 'length' into 'dma_length', and if dma_length was previously uninitialised then I don't see that it can really cause additional problems for ION users. (I hate the way I've been using 'if' a lot so I'm going to spend some time educating myself.) > Acked-by: Laura Abbott Thanks -- Tixy