Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752579AbdGFBo3 (ORCPT ); Wed, 5 Jul 2017 21:44:29 -0400 Received: from mail-yw0-f175.google.com ([209.85.161.175]:35703 "EHLO mail-yw0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751914AbdGFBo2 (ORCPT ); Wed, 5 Jul 2017 21:44:28 -0400 MIME-Version: 1.0 In-Reply-To: <20170705172019.GB5246@lst.de> References: <20170705071215.17603-1-tfiga@chromium.org> <20170705071215.17603-2-tfiga@chromium.org> <20170705151728.GA2479@lst.de> <20170705172019.GB5246@lst.de> From: Tomasz Figa Date: Thu, 6 Jul 2017 10:44:05 +0900 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: [RFC PATCH 1/5] base: dma-mapping: Export commonly used symbols To: Christoph Hellwig Cc: "open list:IOMMU DRIVERS" , "linux-kernel@vger.kernel.org" , Marek Szyprowski , Robin Murphy , Greg Kroah-Hartman , Joerg Roedel , Will Deacon , Vineet Gupta , Hans-Christian Noren Egtvedt , Mitchel Humpherys , Krzysztof Kozlowski , Arnd Bergmann Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2030 Lines: 45 On Thu, Jul 6, 2017 at 2:20 AM, Christoph Hellwig wrote: > On Thu, Jul 06, 2017 at 12:22:35AM +0900, Tomasz Figa wrote: >> Generally the user is a work in progress that should be posted in a >> very near future. You can find a reference to our downstream tree at >> chromium.org in the cover letter. Obviously I don't mind including >> patches from this series in the driver series later and that's one of >> the reasons for this series being RFC. > > Please post and explain them here. That's the intention. I will talk with people to try to get it posted earlier. You can also refer to the old series, which we are reworking to address review comments: https://www.mail-archive.com/linux-media@vger.kernel.org/msg113505.html The old code essentially reimplements all the DMA mapping operations on its own, without using the generic helpers (and not even following the API properly, see my review comments to the original patch 2 and 3), which IMHO is really ugly (but avoids exporting symbols of the helpers, which I assumed to be a no-problem). > In general I think moving dma > ops and iommu implementations into modules is a bad idea Could you elaborate on this? I'd be interested in seeing the reasoning behind this. > but I > don't want to reject the idea before seeing the code. Or maybe > by looking at the user we can come up with an even better idea > to solve the original issue you're trying to solve, so please also > explain your rationale. Basically we have an x86 platform with a camera subsystem that is a PCI device, has its own MMU and needs cache maintenance. Moreover, the V4L2 subsystem, which is the right place for camera drivers, heavily relies on DMA mapping as a way to abstract memory allocation, mapping and cache maintenance. So it feels natural to me to hide the hardware details (additional cache maintenance, mapping into the built-in IOMMU) in the DMA mapping ops for this camera subsystem and simply make V4L2 just work without knowing those details. Best regards, Tomasz